GRB990123 BATSE Trigger Time= 09:46:58 UT BATSE Trigger 7343 BATSE Description: Duration ~110 sec. Strong, multipeaked, seen above 300keV. This file is updated in real-time, so hit to update your browser cache. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 199 SUBJECT: GRB990123, BeppoSAX WFC detection and NFI planned follow-up DATE: 99/01/23 14:53:46 GMT FROM: Luigi Piro at IAS/CNR Frascati Luigi Piro on behalf of the BeppoSAX team report: On Jan.23, 9:47:14 UT BeppoSAX GRBM has been triggered by a burst, GB990123 (also BATSE trigger n.7343), the strongest detected so far simultaneously with the WFC. Preliminary coordinates from WFC are: R.A.(2000)= 231.374 DEC(2000)= +44.754 with an error radius of about 5' A follow-on with NFI is being planned. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 200 SUBJECT: GRB 990123, Radio observations DATE: 99/01/23 16:24:28 GMT FROM: Dale A. Frail at NRAO D. A. Frail (NRAO), and S. R. Kulkarni (Caltech) report on behalf of a larger NRAO/Caltech collaboration: "We observed the error box of GRB 990123 (GCN #199) beginning January 23.63 UT with the Very Large Array (VLA) at 8.46 GHz. There are no radio sources brighter than 170 microJy (5-sigma) in the WFC error circle. Further observations are planned." This message is citeable. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 201 SUBJECT: GRB 990123: Bright New Source, Possible Optical Transient DATE: 99/01/23 17:18:18 GMT FROM: Josh Bloom at CIT GRB 990123: Bright New Source, Possible Optical Transient S. C. Odewahn, J. S. Bloom, and S. R. Kulkarni (CIT) report on behalf of the Caltech-NRAO-CARA GRB Collaboration: "We imaged the BeppoSAX localization (Piro et al. 1999; GCN #199) of GRB 990123 with a CCD camera on the Palomar 60-inch. In each 400-s R-band image a source clearly brighter than on DSS was seen at position: RA,DEC = 15:25:30.53, +44:46:00.5 (J2000) (preliminary astrometry). This localization is well-within the BeppoSAX error radius. Though DSS and R-band are somewhat different bandpasses, given the apparent brightness of the source relative to the DSS image, we suggest that this source is the optical transient of GRB 990123. A faint source at the limit of detectability is seen on the POSS-II image at this location and we suggest this may is the host galaxy of the GRB. If true, we have discovered the brightest host galaxy of any GRB known thus far --- this would be commensurate with the expectation, based on the high GRB flux as measured by BeppoSAX, that this burst is nearer than any localized previously. Preliminary photometry based on the APM catalogue puts the optical transient at R = 18.2 (Jan 23.565 UT) and the host galaxy at R ~= 21.3. More precise photometric and astrometric calibrations are currently under way. The discovery image may be obtained at the following web page: http://astro.caltech.edu/~jsb/GRB/grb990123.html Follow-up of this most bright burst is urged at all wavelengths. This message may be cited." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 202 SUBJECT: GRB990123, refined SAX-WFC position DATE: 99/01/23 17:55:33 GMT FROM: Luigi Piro at IAS/CNR Frascati Luigi Piro on behalf of the BeppoSSAX team report: Refined coordinates for GRB990123 from the WFC are: R.A.(2000)= 231.369 DEC(2000)= +44.758 i.e. 0.3' away from the preliminary position. The error radius is 2'. The follow-on with NFI should start around 15:40 UT, i.e. less than 6 hr after the burst. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 203 SUBJECT: GRB990123, BeppoSAX-NFI X-ray afterglow detection DATE: 99/01/23 18:47:56 GMT FROM: Luigi Piro at IAS/CNR Frascati Luigi Piro on behalf of the BeppoSAX team report: A BeppoSAX follow-up of GRB990123 initiated around 15:40 UT, i.e. 6 hr after the burst. Preliminary analysis of the first 20 minutes of the data at SOC shows a previously unknown strong source (about 10**-11 c.g.s in the 1.6-10 keV) in the center of the WFC error circle. Preliminary coordinates are: R.A.(2000)= 231.374 DEC(2000)= +44.758 The error radius is 1.5'. Considering its strenght, this X-ray source is very likely the X-ray afterglow of GB990123. We will continue to observe it to monitor its temporal evolution. //////////////////////////////////////////////////////////////////////// Circular No. 7094 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A. IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions) BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science) URL http://cfa-www.harvard.edu/iau/cbat.html ISSN 0081-0304 Phone 617-495-7244/7440/7444 (for emergency use only) GRB 990123 S. C. Odewahn, J. S. Bloom, and S. R. Kulkarni, California Institute of Technology, report on behalf of the Caltech-NRAO-CARA GRB Collaboration: "On Jan. 23.56 UT, we imaged the BeppoSAX localization (Piro et al. 1999, GCN 199, http://gcn.gsfc.nasa.gov/gcn/gcn3/199.gcn3) of GRB 990123 with the Palomar 1.52-m reflector (+ CCD). We found a source (R = 18.2) located at R.A. = 15h25m30s.5, Decl. = +44o46'00" (equinox 2000.0; GCN 202 gives a revised BeppoSAX position of R.A. = 15h25m29s, Decl. = +44o45'.5). The error in the position (derived from the Digital Sky Survey) is about 1".5. At the same location, no object is detected to the plate limit of the first Palomar Sky Survey, whereas a faint (R about 21.3) object is seen in the second Palomar Sky Survey image. The photometry is preliminary and is based on the Cambridge Automated Plate Machine catalogue. Finding charts can be found at http://astro.caltech.edu/~jsb/GRB/grb990123.html; see also GCN 201. We suggest that the bright object is the optical afterglow of GRB 990123 and that the faint object is the host galaxy. If so, this is the brightest optical afterglow and host galaxy known to date. In view of this, we urge observations at all wavelengths and particularly spectroscopic observations of this object." (C) Copyright 1999 CBAT 1999 January 23 (7094) Daniel W. E. Green //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 204 SUBJECT: GRB990123 Optical Observation DATE: 99/01/23 22:44:31 GMT FROM: Jin Zhu at Beijing Obs GRB 990123 Optical Observation J. Zhu, H. T. Zhang, on behave of the Beijing Astronomical Observatory GRB team, report: "R-band image of the BeppoSAX WFC error circle of GRB 990123 (Piro, GCN #199) were obtained on 1999 Jan 23.756 UT, 8.5 hours after the GRB, with the BAO 0.6/0.9m Schmidt telescope in Xinglong. The weather was bad, so only one 20-min. exposure image taken under thin cloud was usable (FWHM=6"). Central part of the image is posted at http://vega.bac.pku.edu.cn/~zj/grb/grb990123.gif. A faint object could be seen closed to the optical candidate position suggested by S. C. Odewahn et al. (GCN, #201). Its position from our measurement is RA=15:25:30.28, Dec=+44:45:59.0 (1 sigma = 0.5"), with magnitude of 19.2 (+/- 0.5 ?) if using the following 4 stars' magnitude information from the USNO-A V1.0 catalogue (David Monet, et. al.): ========================================================= No. RA_mea (2000.0) Dec_mea RA_cat (2000.0) Dec_cat mag. --- ----------------------- ----------------------- ---- 1 15:25:27.03 +44:46:23.3 15:25:27.04 +44:46:23.2 14.4 2 15:25:36.47 +44:44:37.6 15:25:36.45 +44:44:37.6 15.3 3 15:25:32.57 +44:44:29.9 15:25:32.66 +44:44:29.9 18.5 4 15:25:27.42 +44:44:42.5 15:25:27.48 +44:44:43.6 19.7 ========================================================= The object in our image seems slightly extended and slightly southwest comparing with the discovery image of Odewahn et al., but it seems to be impossible to confirm from only one image in not good quality. However, it could be concluded that if such an object (in our image) would not be real, the optical transient in Odewahn et al.'s images must be faded largely between the 4.6 hours interval. This report may be cited." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 205 SUBJECT: GRB990123, early optical counterpart detection DATE: 99/01/23 23:15:16 GMT FROM: Carl Akerlof at U.Michigan C. W. Akerlof and T. A. McKay (Univ. of Michigan) report on behalf of the ROTSE collaboration (Michigan/LANL/LLNL): We observed the error box of GRB 990123 provided by the BACODINE Burst Position Notice dated 23-Jan-99 09:46:59 using the ROTSE-I telephoto camera array located at Los Alamos, New Mexico. The first exposure began at 9:47:18.30, 22.18 seconds after the nominal burst trigger time. A rapidly fading object was discovered at the coordinates, RA = 231.3754, DEC = 44.7666 (J2000) which is within 1/3 of a pixel of the optical counterpart reported by Odewahn et al. (GCN #201). The light curve for this object is relatively complex: the luminosity increases by 3 magnitudes between the first and second exposures. Estimated magnitudes for the first six exposures are given below: UTC exposure m_v 9:47:18.3 5 secs. 11.82 9:47:43.5 5 secs. 8.95 9:48:08.8 5 secs. 10.08 9:51:37.5 75 secs. 13.22 9:54:22.8 75 secs. 14.00 9:57:08.1 75 secs. 14.53 Note that the ROTSE-I detector system uses an unfiltered broadband CCD so that magnitude estimates are based on comparisons to catalog values for nearby stars. Sky patrol images of the same coordinates taken 133 minutes earlier showed no evidence of the transient to a limit of at least two magnitudes deeper. A more extensive analysis of this data will be available in the near future. The discovery images will be posted on the ROTSE Web page at: http://www.umich.edu/~rotse/gifs/grb990123/990123.gif This message is quotable in publications. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 206 SUBJECT: GRB 990123 Optical Follow-up DATE: 99/01/24 00:01:51 GMT FROM: Josh Bloom at CIT GRB 990123 Optical Follow-Up J. S. Bloom, R. R. Gal, L. L. Lubin, J. Mulchaey, S. C. Odewahn (CIT), S. R. Kulkarni report on behalf of the Caltech-NRAO-CARA GRB Collaboration: "We obtained a single B-band image (300-s) at the Palomar 200-inch of the field of GRB 990123 localized by BeppoSAX (GCN #200). Using images obtained of the Landolt standard field 98, we derived a photometric zeropoint for the GRB data. The transient first reported in Odewahn, Bloom, Kulkarni (GCN #202) is well-detected at B = 18.93 +/- 0.03 mag (Jan 23.578 UT). The uncertainty includes the systematic and statistical uncertainties though no color term was applied. For reference, we find the following B = 19.59 +/- 0.04 for the object at position ra: 15:25:32.7, dec: +44:44:29.7 (J2000). Absolute astrometry was obtained by comparison of 34 objects near the optical transient with the USNO-A2.0 Catalogue. The r.m.s. uncertainties of the astrometry are 0.28 arcsec (ra) and 0.26 arcsec (dec). We find the position of the optical transient to be, ra: 15:25:30.34, dec: +44:45:59.1 (J2000). Based on the POSS-II F-Plate of this field, the purported host galaxy (see GCN #202) appears offset from the OT by 1.8 arcsec (+/- 0.4 arcsec) to the South. Further analysis is underway. This message may be cited." //////////////////////////////////////////////////////////////////////// Circular No. 7095 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A. IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions) BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science) URL http://cfa-www.harvard.edu/iau/cbat.html ISSN 0081-0304 Phone 617-495-7244/7440/7444 (for emergency use only) GRB 990123 Further to the item on IAUC 7094, M. Feroci and L. Piro, Istituto di Astrofisica Spaziale, CNR, Rome; F. Frontera, Istituto Tecnologie e Studio Radiazioni Extraterrestri, CNR, Bologna, and University of Ferrara; V. Torroni and M. Smith, BeppoSAX Science Operation Center, Telespazio, Rome; and J. Heise and J. in 't Zand, Space Research Organization of the Netherlands, Utrecht, provide the following elaboration of the information given on GCN 199 and 202: "A gamma-ray burst triggered the BeppoSAX Gamma-Ray Burst Monitor (GRBM) on Jan. 23.40780 UT. The burst was also detected in the Wide Field Camera (WFC) 1. The GRBM lightcurve shows a multipeak complex structure that lasts for about 100 s with two major peaks. The intensity of the highest peak is 11 200 counts/s in the band 40-700 keV. A preliminary estimation of the fluence is (3.5 +/- 0.4) x 10E-4 erg cmE-2 sE-1. This is the brightest burst detected so far by the BeppoSAX GRBM simultaneously with the WFC. The WFC lightcurve, which lasts for a comparable time, is also complex, with one peak followed by a structured, higher plateau. The WFC peak intensity corresponds to a flux of 3.4 Crab in the energy band 1.5-26 keV, and it is reached about 40 s afterthe GRBM peak. The position of the x-ray counterpart to GRB 990123, as derived by the quicklook WFC image, is R.A. = 15h25m29s, Decl. = +44o45'.5 (equinox 2000.0), with an error radius of 2' (99-percent confidence level). A follow-up observation with BeppoSAX narrow- field instruments is in progress." J. Zhu and H. T. Zhang, on behalf of the Beijing Astronomical Observatory (BAO) GRB team, write: "R-band images of the BeppoSAX WFC error circle of GRB 990123 were obtained on Jan. 23.756 UT (8.5 hr after the GRB) with the BAO 0.6-m Schmidt telescope at Xinglong. Due to bad weather, only one 20-min exposure image taken in thin cloud was usable (FWHM = 6"). The central part of the image is posted at http://vega.bac.pku.edu.cn/~zj/grb/grb990123.gif. A faint object could be seen close to the optical candidate position suggested by S. C. Odewahn et al. (IAUC 7094); its position from our measurement is R.A. = 15h25m30s.28, Decl. = +44o45'59".0 (1-sigma = 0".5), with a magnitude of 19.2 (+/- 0.5?) from four stars in the USNO-A V1.0 catalogue. The object in our image seems slightly extended and slightly to the southwest, compared with the discovery image of Odewahn et al., but it seems to be impossible to confirm from only one image of poor quality. However, it could be concluded that if such an object (in our image) is not real, the optical transient in Odewahn et al.'s images must have faded greatly during the 4.6-hr interval." (C) Copyright 1999 CBAT 1999 January 23 (7095) Daniel W. E. Green //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 207 SUBJECT: GRB 990123 r-band photometry DATE: 99/01/24 03:33:59 GMT FROM: Shri Kulkarni at Caltech GRB 990123 r-band Photometry R. R. Gal, S. C. Odewahn, J. S. Bloom, S. R. Kulkarni (CIT), D. A. Frail (NRAO) report on behalf of the Caltech-NRAO-CARA GRB Collaboration: "We report on a detailed analysis of images obtained at the Palomar 60-inch telescope, the initial results of which were reported in GCN 201. Three images of 400-s duration each were obtained of the field of GRB 990123 localized by BeppoSAX (GCN #200). These images were obtained in the Gunn r-band and not R band as reported in GCN #201. The seeing was 1.7 arcsec (FWHM) in each image. Using images obtained of two Gunn standards (Feige 34 and Feige 67), we obtained a photometric zero point for the data. The observation times and magnitudes for the optical transient reported in Odewahn, Bloom, Kulkarni (GCN #202) and the reference star from Bloom et al. (GCN #206) are: Gunn-r Mag UT (23 Jan 1999) OT Ref. Star --------------------------------------------------------- 13:37:20.3 18.70 +/- 0.04 19.10 +/- 0.04 13:51:03.6 18.78 +/- 0.04 19.11 +/- 0.04 14:02:56.5 18.75 +/- 0.06 19.07 +/- 0.06 -------------------------------------------------------- The uncertainty in the magnitudes include the systematic and statistical uncertainties, although no color term was applied. We note that the second r-band image was taken nearly simultaneous with the B-band image discussed in Bloom et al. (GCN #206). The Galactic extinction in the direction of the optical transient (l,b = 73.12, 54.64) is E(B-V) = 0.01597 (Schlegel, Finkbeiner, and Davis; 1998 ApJ, 500, 525). Thus (assuming Rv = 3.1), A_B = 0.069 and A_gunnr = 0.041. The extinction corrected magnitudes of the transient at epoch Jan 23.578 1999 UT are thus B = 18.86 and Gunn-r = 18.74. Assuming the bandpass zeropoints and effective central wavelength of the Johnson B and Gunn-r bandpasses from Fukugita, Shimasaku, and Ichikawa (1995 PASP, 107, 945) we get F(B)= 115 microJy F(r) = 94 microJy. Thus the power law slope beta = 0.5 where beta = log F(nu/log(nu). the transient is blue with a spectral index of beta = 0.5 (with beta =dlog F(nu)/dlog nu). This spectral behavior has not been seen in previous GRB afterglows. In the framework of the afterglow models, this result can be interpreted to mean that the flux from the afterglow did not peak in the optical bands by the epoch of our second r-band image. This message may be cited." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 208 SUBJECT: GRB 990123: Optical Decay Slope DATE: 99/01/24 09:12:10 GMT FROM: Josh Bloom at CIT GRB 990123: Optical Decay Slope J. S. Bloom, S. R. Kulkarni, S. G. Djorgovski, S. C. Odewahn, R. R. Gal, L. M. Lubin (CIT), and D. A. Frail (NRAO) note on behalf of the Caltech-CARA-NRAO GRB collaboration: "After an initial rise to about 1 Jy, the early-time optical light-curve of the transient afterglow of GRB 990123 (as reported by the ROTSE Team; GCN #205) displayed a power-law decay. We note here that the decay appears to be well-continued by the later time (~3 hours) optical fluxes of the transient discovered at Palomar (GCN #201; GCN #206; GCN #207). The decay constant is approximately alpha = -1.5 (defined as F_nu (t) = const * t^alpha). This is consistent with the decay constants measured at late-times in other GRB afterglows. This suggests a strong phenomenological connection between the emission mechanism(s) at very early times (from tens of seconds to few minutes after the burst) and at later times (>~ few hours). The continuity of the power-law light curve represents a strong constraint for theoretical models of optical emission from GRBs and their afterglows. A lightcurve, which will be actively updated, may be obtained at http://astro.caltech.edu/~jsb/GRB/grb990123.html This message may be cited." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 209 SUBJECT: GRB990123, Optical observation DATE: 99/01/24 13:26:03 GMT FROM: Luciano Nicastro at IFCAI-CNR GRB990123 Optical Observation at SAO-RAS V. Sokolov, S. Zharikov (SAO-RAS) and L. Nicastro, M. Feroci, E. Palazzi on behalf of the BeppoSAX team report: We obtained an R-band image of the BeppoSAX localization of GRB990123 on 1999 Jan 24.076 UT, 16.04 hours after the GRB event, with the SAO-RAS 6-m telescope. The weather was cloudy. In spite of that, in a 15-min exposure image we were able to see an object at the position of the optical candidate suggested by Odewahn et al. (GCN #201). We estimated a magnitude of 19.6 +/- 0.2 (using star 1 from GCN #204) and 19.9 +/- 0.2 (using star 2 from GCN #204). These values include the contribution of the proposed underlying host galaxy. To have the contribution of the OT alone these value should be increased by about 0.25 magnitudes. R = 19.9 +/- 0.2 is compatible with the power-law decay with index -1.5 found by Bloom et al. (GCN #208) as we would expect to find about R = 20.1 using the R = 18.2 on Jan 23.565 UT and R = 21.3 for the underlying galaxy (GCN #201). This report may be cited. [GCN OP NOTE: This circular was actually received at 12:40:01 UT, but was delayed in distribution due to the submitter not having prior vetting.] //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 210 SUBJECT: GRB990123 optical observations DATE: 99/01/24 15:35:49 GMT FROM: Paul Vreeswijk at U of Amsterdam Eran Ofek and Elia M. Leibowitz, Wise Observatory, Tel Aviv University report: >From 4 CCD frames of the object taken at the WO between Jan 24.0617-24.1162 we have determined an average R magnitude of 19.87+-0.2, with calibration based on 4 USNO A2.0 stars. The decay parameter in the R band over that time interval is -1.9+-0.1. On Jan 24.0625, the color index of the object was B-R=-0.48+-0.25. This report may be cited. //////////////////////////////////////////////////////////////////////// Circular No. 7096 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A. IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions) BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science) URL http://cfa-www.harvard.edu/iau/cbat.html ISSN 0081-0304 Phone 617-495-7244/7440/7444 (for emergency use only) GRB 990123 R. Lachaume and O. Guyon, Institut d'Astrophysique, Paris, report their locating the optical candidate at the expected position (cf. IAUC 7094, 7095) on two 30-min CCD exposures with the 1.2-m telescope of the Observatoire de Haute Provence, yielding the following magnitudes (from nine USNO A2.0 catalogue stars), with 1-sigma uncertainties of +/- 0.15 mag: Jan. 24.15 UT, B = 18.40; 24.17, R = 19.45. E. Ofek and E. M. Leibowitz, Tel Aviv University, write: "From four CCD frames of the object taken at the Wise Observatory between Jan. 24.0617 and 24.1162 UT, we have determined an average R magnitude of 19.87 +/- 0.2, with calibration based on four USNO A2.0 stars. The decay parameter in the R band over that time interval is -1.9 +/- 0.1. On Jan. 24.0625, the color index of the object was B-R = -0.48 +/- 0.25." D. D. Kelson, Department of Terrestrial Magnetism, Carnegie Institution of Washington; G. D. Illingworth, University of California at Santa Cruz (UCSC); M. Franx, University of Leiden; D. Magee, UCSC; and P. G. van Dokkum, Kapteyn Astronomical Institute, Groningen, report: "Three 10-min spectra were taken of the proposed optical counterpart to GRB 990123 (IAUC 7094) with the Keck II 10-m telescope on Jan. 24.6 UT. The spectra show the following ultraviolet absorption lines: Fe II (234.4, 237.5, and 238.3 nm), Fe II (258.7 and 260.0 nm), Mg II (279.6 and 280.3 nm), and Mg I (285.2 nm). The redshift is z = 1.61. No strong emission lines were detected between 460 and 920 nm." (C) Copyright 1999 CBAT 1999 January 24 (7096) Daniel W. E. Green //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 211 SUBJECT: GRB 990123, new radio source DATE: 99/01/24 16:56:38 GMT FROM: Dale A. Frail at NRAO D. A. Frail (NRAO), and S. R. Kulkarni (Caltech) report on behalf of a larger NRAO/Caltech collaboration: "We obtained a second VLA observation of the error box of GRB 990123 (GCN #199) beginning on January 24.65 UT at 8.46 GHz. At the location of the optical transient (GCN #201) there is a new radio source with a flux density of 260 +/- 32 microJy. A similar image taken on January 23.63 UT (GCN# 200) gives a 2-sigma upper limit at this same location of 64 microJy. We are likely observing the slow "turn-on" of the afterglow. Further observations are planned to track its expected rise to maximum and its subsequent power-law decay." This message is citeable. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 212 SUBJECT: GRB 990123 radio observations DATE: 99/01/24 19:19:16 GMT FROM: Titus Galama at U.Amsterdam T.J. Galama, P. Vreeswijk, E. Rol (U. of Amsterdam), R. Strom (NFRA and U. of Amsterdam), J. van Paradijs (U. of Amsterdam and U. of Alabama in Huntsville), C. Kouveliotou (USRA/MSFC), G. de Bruyn (NFRA and U. of Groningen) report: "We observed the error box of GRB 990123 (GCN #199) at 4.88 GHz with the Westerbork Synthesis Radio Telescope (WSRT) for 12 hours on January 24.28 1999 UT. At the position of the optical transient (GCN #201) we do not detect a radio source (< 130 microJansky; 3 sigma). This result, when compared with the January 24.65 UT 8.46 GHz VLA detection (260 +/- 32 microJansky; GCN #211) may be due to synchrotron self-absorption, or otherwise, may indicate that the 4.88 GHz observation was suppressed by interstellar scintillation. Further observations are planned." This message is citeable. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 213 SUBJECT: GRB 990123: Pre-Burst Detection of an Apparent Host Galaxy DATE: 99/01/24 22:11:08 GMT FROM: George Djorgovski at Caltech/Palomar GRB 990123: Pre-Burst Detection of an Apparent Host Galaxy R. R. Gal, S. G. Djorgovski, S. C. Odewahn, J. S. Bloom, and S. R. Kulkarni (CIT), on behalf of the Caltech DPOSS team and the Caltech-CARA-NRAO GRB collaboration report: A faint galaxy coincident with the optical transient discovered at Palomar (Odewahn et al., GCN Circ. 201 and IAUC 7094) was detected on the F (red) plate of Digital POSS-II (DPOSS), taken on 05 July 1994 UT. The galaxy was not detected on J (blue/green) and N (near-IR) plates taken in March 1993. Using the new CCD calibration of the field, we obtain for the galaxy the Gunn magnitude r = 21.9 +- 0.4 (corresponding to Johnson R = 21.5 +- 0.5). Our preliminary calibration gives the upper limits in the other two band, with g > 22.4 (roughly, B > 22.0), and i > 20.6 (roughly, I > 19.9), with a net uncertainty of about 0.5 mag. The limits in g and i are consistent with the plate limits and the weak detection in the r band, for typical galaxies at these magnitude levels. At this r band magnitude level, the typical redshift for a normal field galaxy is about 0.2 to 0.3. It is extremely unlikely that this galaxy is at z > 0.5, unless it contains an active nucleus. Future spectroscopic observations will establish if this is indeed the host galaxy of GRB 990123. The DPOSS image can be seen at: http://astro.caltech.edu/~george/grb/grb990123.html This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 214 SUBJECT: GRB 990123 optical observations DATE: 99/01/25 01:30:13 GMT FROM: James Rhoads at KPNO E. Falco, C. Petry, C. Impey, A. Koekemoer, and J. Rhoads report on behalf of the KPNO GRB Followup team: Falco, Petry, and Impey have observed the optical counterpart of GRB 990123 in U band on 1999 January 24.497 UT using the 4 meter Mayall telescope and CCD Mosaic Camera at Kitt Peak National Observatory. Conditions were non-photometric with 1.3 arcsecond seeing. The counterpart (cf. Odewahn et al, GCN 201) is clearly detected. Absolute flux calibration is not yet possible, but the transient is approximately 1.1 magnitude fainter than the reference object at position RA=15:25:32.7, dec=+44:44:29.7 (J2000). The statistical uncertainty in the flux should be of order 3%. The counterpart is a point source in our data, suggesting that host galaxy flux contributes only a small fraction of the current U band brightness. We suggest that the afterglow may be bluer than the host galaxy; if so, U band would be a good wavelength to follow its light curve to late stages. In addition, Koekemoer has observed the counterpart at K band on 1999 January 24.546 UT using the 2.1 meter telescope and ONIS near-infrared camera at Kitt Peak National Observatory. Total exposure time was 600 seconds. The transient is not readily apparent in the coadded image. The rough limiting magnitude of the K band image can be estimated from the USNO-A1 catalog, which gives Red and Blue magnitudes 14.4 and 15.5 for a star with signal to noise ratio 10 in the combined K band image. More careful processing might improve this limit modestly. Combining these two measurements will yield a limit on the spectral slope of the afterglow. A section of the U band image is available at http://www.noao.edu/noao/grb/990123.html . This report is citable. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 215 SUBJECT: GRB990123, optical observation DATE: 99/01/25 01:50:49 GMT FROM: Peter Garnavich at CfA P. Garnavich, S. Jha, K. Stanek and M. Garcia (Center for Astrophysics) report "an R-band image of the GRB990123 field was obtained with the Fred L. Whipple Observatory 1.2m telescope and CCD camera on Jan 24.547 UT. The Optical Tranisent (plus host galaxy) are easily visible and comparison with star-3 of GCN Circular 204 (R=18.5) gives an R magnitude of 20.4 for the OT+galaxy. This is consistent with the continuing t**(-1.5) decline shown by Bloom et al. (GCN 208)." This message is quotable in publications. [GCN OP NOTE: This circular was actually received at 17:59:03 UT, but was delayed in distribution due to the submitter not having prior vetting.] //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 216 SUBJECT: GRB 990123: Possible Gravitationally Lensed Burst? DATE: 99/01/25 01:57:11 GMT FROM: George Djorgovski at Caltech/Palomar GRB 990123: Possible Gravitationally Lensed Burst? S. G. Djorgovski, S. R. Kulkarni, J. S. Bloom, S. C. Odewahn, R. R. Gal (CIT), and D. A. Frail (NRAO) note on behalf of the Caltech-CARA-NRAO collaboration: The lower limit to redshift of GRB 990123 (Kelson et al., IAUC, 7096), z =< 1.61, implies a luminosity distance D >= 3.73e28 cm, assuming a standard Friedmann cosmology with H_0 = 65 km/s/Mpc, Omega_0 = 0.2, and Lambda_0 = 0 (larger if Lambda_0 > 0). Assuming the gamma-ray fluence reported by Feroci et al. (IAUC 7095), the implied isotropic gamma-ray energy of this burst would be > 2.3e54 erg, higher than most (or all) currently viable theoretical models can easily accomodate. The absolute magnitude of the optical counterpart at maximum light (Akerlof and McKay, GCN Circ. 205) would be M =< -36.5, i.e., > 2e16 L_sun, a remarkable number itself. The apparent host galaxy of this burst, coincident with the optical transient (Odewahn et al., GCN Circ. 201 and IAUC 7094) detected on DPOSS (digital POSS-II) images calibrated with new CCD photometry in the field, has a Gunn r magnitude 21.9 +- 0.4, i.e., R ~ 21.5 +- 0.5 (cf. Gal et al., GCN Circ. 213). Its probable redshift is likely to be approximately 0.2 to 0.3, and (unless an active nucleus is present, for which there is no spectroscopic evidence so far) almost certainly not at z = 1.61, the absorption line redshift measured by Kelson et al. We therefore suggest that this may be the first documented case of a gravitationally lensed GRB, magnified by at least an order of magnitude by a foreground galaxy detected in DPOSS (possibly including some microlensing). This hypothesis naturally accounts for all of the data so far: the large fluence of the burst, its enormous implied gamma-ray luminosity, its remarkably high peak optical brightness and implied luminosity (and makes it consistent with previous non-detections of other bursts by the ROTSE and LOTIS experiments, with m_lim ~ 14), and the presence of an apparent foreground galaxy positionally coincident with the optical transient. The conclusive test of this hypothesis will be a direct measurement of the galaxy's redshift, once the OT fades sufficiently. If microlensing is involved, a signature may be seen in the shape of the OT light curve. Possible image splitting may be detectable, and high-resolution imaging in radio, near-IR, and optical is urged. In any case, the early detection by the ROTSE team (GCN Citc. 205), even if corrected for a putative large gravitational lensing magnification factor, suggests that routine early detections of GRBs in the visible light are within reach, perhaps at ~ 15 mag level. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 217 SUBJECT: GRB 990123 Optical Follow-Up DATE: 99/01/25 08:19:31 GMT FROM: Jin Zhu at Beijing Obs GRB 990123 Optical Follow-Up J. Zhu, J. S. Chen, and H. T. Zhang, on behalf of the Beijing Astronomical Observatory GRB team report: "We observed the GRB 990123 OT (GCN #202) during Jan. 24.730-24.861 with BAO 0.6-m Schmidt telescope under non-photometric weather. Combination of two relatively best quality 60-min. images taken with BATC band-i filter (central wavelength at 6660 A, band width 480 A) gives a detection of the object (OT+galaxy) at RA=15:25:30.17, Dec=+44:45:59.7 (J2000) with magnitude of 21.0 +/- 0.3 (Jan 24.818) using the No. 1 and No. 2 stars in GCN #204. No visual seperation between OT and galaxy could be recognized because of low S/N ratio and bad spatial resolution (1 pixel = 1.7", seeing = 5.6"). Central 4' X 4' part of the whole 58' X 58' CCD field will soon be available under http://vega.bac.pku.edu.cn/~zj/grb/grb990123.html Re-reduction of GCN #204 observation with only first 2 of the 4 stars gives same result for the OT+galaxy in magnitude of 19.2 +/- 0.1 (Jan 23.756). This report may be cited." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 218 SUBJECT: GRB 990123: New Optical Observations, Decay Measure DATE: 99/01/25 10:34:08 GMT FROM: Josh Bloom at CIT GRB 990123: New Optical Observations, Decay Measure J. S. Bloom, S. R. Kulkarni, S. G. Djorgovski, S. C. Odewahn (CIT), R. Sagar, A. K. Pandey, Neelakshi, R. K. S. Yadav (U. P. State Observatory, India) report on behalf of the Caltech-NRAO-CARA GRB collaboration: "On 24.0 Jan 1999 UT, we imaged the optical transient (GCN #201) of GRB 990123 (GCN #199) with the 1.04-m UPSO telescope, India. In one 50-minute B-band image the transient is well-detected at B = 20.16 +/- 0.15 (Jan 23.958 UT). The transient is also well-detected in a 60-minute stacked R-band exposure at gunn-r = 20.02 +/- 0.11. The B-band image was calibrated to the zeropoint of GCN #206 with a set of secondary stars in the OT field. The R-band photometry was tied the gunn-r system using the Palomar 60-inch photometry (#207). The error associated with the calibration between the two somewhat different bandpasses is small compared to the statistical uncertainties. These measurements have not been corrected for Galactic extinction which would amount to A_B = 0.069 and A_r = 0.041 (GCN #207). With the Galactic extinction correction, the transient still blue (ie. has a positive spectral index beta ~= 0.3) at this second epoch (see GCN #207). Assuming a power-law decay (f_nu[nu] = const*t^alpha) we find alpha_B = -0.90 +/- 0.11 (between Jan 23.58 and Jan 23.95) alpha_r = -1.04 +/- 0.14 (between Jan 23.56 and Jan 24.00) This decay is significantly flatter than alpha = -1.5 found at earlier times (ie. t <= Jan 23.5; GCN #208). A recalibration of the transient magnitude reported by Garnavich et al. (GCN #215) using the reference star from Gal et al. (GCN #207), gives r = 21.0 (errors not reported) on Jan 24.547 UT. This implies a decay of alpha = -1.26, consistent with that found above. An updated light-curve may be obtained at http://astro.caltech.edu/~jsb/GRB/grb990123.html This message may be cited." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 219 SUBJECT: GRB 990123 Spectroscopic Redshifts DATE: 99/01/25 11:22:11 GMT FROM: Jens Hjorth at U.Copenhagen GRB 990123 Spectroscopic Redshifts J. Hjorth (Copenhagen), M. I. Andersen (NOT), L. M. Cairos, N. Caon, M. Zapatero Osorio (IAC), H. Pedersen, B. Lindgren (Copenhagen), A. J. Castro Tirado (LAEFF, IAA), and E. Perez (IAA) report: "Three 40 min spectra of GRB 990123 were obtained at NOT on Jan 24.24 UT 1999. Based on a preliminary reduction and analysis we detect the following ultraviolet absorption lines: Si II (152.6 nm), C IV (154.9 nm), Fe II (160.8 nm), Al II (167.1 nm), Zn II (202.6 and 206.3 nm), Fe II (234.4, 237.5, and 238.3 nm), and Fe II (258.7 and 260.0 nm) at a redshift of 1.600 +- 0.001. This value is in agreement with the redshift found by Kelson et al. (IAU Circ. 7096). Several additional absorption lines and two emission lines are detected. There is one definite system at z = 0.286 +- 0.001 based on [OII] (372.7 nm) emission and Ca H and K (393.3 nm and 396.9 nm) absorption and another possible system at z = 0.210 +- 0.002 based on [OII] emission and Ca K absorption. One of these systems are likely to be associated with the galaxy located 1.8 +- 0.4" from the optical transient (Bloom et al., GCN Circ. 206). This galaxy has an estimated redshift of z ~ 0.2 - 0.3 (Gal et al., GCN Circ. 213). These observations support the idea that GRB 990123 may be a gravitationally lensed gamma-ray burst (Djorgovski et al. GCN Circ. 216). The 'source' (optical transient) redshift (z >= 1.60) and 'lens' (galaxy) redshift(s) (z = 0.29, z = 0.21) as well as the angular separation between the image and the lens are typical of those found among multiply imaged QSOs. The existence of several galaxies along the line of sight to the GRB enhances the lensing cross section. If GRB 990123 is multiply lensed, a fainter GRB is expected to appear 2-3" north of GRB 990123, within a time scale of months. In addition, two more GRBs may appear within days or weeks from now if GRB 990123 is quadruply lensed. Continued monitoring is urged at all wavelengths in order to determine precise time delay(s). The results reported in this circular are preliminary. A more detailed analysis is ongoing." This report may be cited. [GCN OP NOTE: This archived copy of Circular 219 has been reformatted by the author, i.e. different than the copy actually distributed.] //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 220 SUBJECT: GRB990123 Optical Observations DATE: 99/01/25 15:30:47 GMT FROM: Michel Boer at CESR-CNRS A. Maury (Observatoire de la Cote d'Azur), M. Boer, S. Chaty (Centre d'Etude Spatiale des Rayonnements), report: We observed GRB 990123 from the Observatoire de la Cote d'Azur 0.9m Schmidt Telescope. The optical counterpart of the GRB is clearly detected as well as the host galaxy. Below are the unfiltered magnitudes, corresponding approximately to R magnitudes, given the detector response. The mean uncertainty is 0.4 mag. The resulting decay slope, is 1.35, which is in good agreement with the slope mentionned by Bloom et al. (GCN Report #208), given the uncertainties. January 24.037037 19.68 24.052419 19.67 24.057234 20.02 24.061887 19.79 24.066539 19.71 24.071192 19.44 24.075845 20.4 24.080498 19.92 24.08515 20.05 24.094456 20.25 24.099109 20.15 24.113067 19.65 24.117731 19.82 24.122373 20.22 24.127025 20.53 24.131678 20.32 24.136331 20.49 24.140984 20.15 24.145637 19.98 24.150289 20.06 24.154942 20.44 24.159595 20.42 24.164248 20.03 24.1689 20.11 24.178206 20.23 24.182859 20.06 24.201076 20.36 Other images have been taken during the night 24-25/1/99 and will be reported later. [GCN OP NOTE (99/01/26 23:47 UT): An ammended version (extra column trailing removed and institutional affiliations added) of this circular was added to the archive at the authors request. The original distributed version suffered from extraneious material from the mailer utility used to create the posting.] //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 221 SUBJECT: GRB 990123 : Multiple and Distorted Images of the Host Galaxy? DATE: 99/01/25 17:07:56 GMT FROM: Ed Turner at PrincetonU. GRB 990123 : Multiple and Distorted Images of the Host Galaxy? E. L. Turner (Princeton Univ. Obsv.): Djorgovski et al. (GCN Circ. 216) suggested that GRB 990123 might be strongly lensed by an intervening galaxy based on the extreme energetics implied by its high gamma-ray fluence (Feroci et al., IAUC 7095) and the redshift lower bound of 1.61 (Kelson et al., IAUC 7096) and on the relatively bright coincident galaxy found on the digital POSS-II images by Odewahn et al. (GCN Circ. 201 and IAUC 7094). Their prediction that this galaxy's redshift would be much smaller than 1.6 and probably in the range 0.2 to 0.3 was quickly confirmed by Hjorth et al. (GCN Circ. 219) who in fact found one definite galaxian redshift system at z = 0.286 and a second possible one at z = 0.210, thus providing strong apparent support for the gravitational lensing hypothesis in GRB 990123. Hjorth et al. also note that additional images of this GRB may appear on a time scale of days to months due to differential lensing time delays. The light from the host galaxy of GRB 990123 will also be affected by any strong gravitational lensing which has influenced the burst and should show strongly distorted and probably multiple images if the magnification factor is large. Detection and characterization of such lensed host galaxy images would provide strong additional evidence for the lensing hypothesis but, more importantly and much more urgently, would also allow detailed modeling of the lensing mass distribution and geometry and, thus, far more precise prediction of where and when additional images of the burst are expected to occur. These predictions would make it far more practical (and economical of observing resources) to detect and intensively study additional images of the burst as they appear. Such data would not only be valuable for probing the early stages of GRB physics but might also allow a sufficiently precise determination of the time delay(s) to use for a measurement of the cosmic distance scale. Thus, deep and high resolution imaging in search of the possibly distorted and multiple images of the GRB 990123 host galaxy is urgently indicated. This report may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 222 SUBJECT: GRB990123 IPN annulus DATE: 99/01/25 18:10:30 GMT FROM: Kevin Hurley at UCBerkeley/SSL K. Hurley, on behalf of the IPN3 team, and M. Feroci, on behalf of the BeppoSAX GRBM team, report: We have obtained a preliminary IPN3 annulus for GRB990123 by triangulation using Ulysses and the BeppoSAX GRBM. The annulus is centered at RA(2000)=163.7197 degrees, Dec(2000)= -9.4661 degrees, with a radius of 81.3372 degrees and a 3 sigma width of 2.67 arcminutes. This annulus reduces slightly both the 2' radius SAX WFC error circle (BeppoSAX MAIL 99/2) as well as the 1.5' MECS error circle (BeppoSAX MAIL 99/3), and contains the optical transient (Bloom et al., GCN 206). An image may be found at ssl.berkeley.edu/ipn3/990123/. Considerable reduction of the annulus width is possible. This report was delayed due to the fact that Ulysses data are not processed and distributed over the weekend. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 223 SUBJECT: GRB 990123 Keck Spectrum update DATE: 99/01/25 21:58:44 GMT FROM: Andrew S. Fruchter at STScI Andy Fruchter reports for Dan Kelson who is in transit: In addition to the z=1.6 metal absorption lines detected in the Keck spectrum of the OT associated with GRB 990123 and reported by Kelson et al. in IAUC 7096, H and K absorption corresponding to a redshift of z~0.2 were found in a nearby galaxy, thus confirming the redshift reported by Hjorth et al. in GCN 219. However, this galaxy is the one visible in the finding chart of Odewahn et al., GCN 201, which lies approximately 10" to the west of the OT. No evidence of lines corresponding to a z~0.2 were found in the Keck spectrum any closer on the sky. [GCN OP NOTE (99/01/26 00:07:21 UT): Please see Addendum revision in GCN 225.] //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 224 SUBJECT: GRB 990123: BATSE Observations DATE: 99/01/25 22:18:55 GMT FROM: R. Marc Kippen at BATSE/UAH/MSFC R. M. Kippen (University of Alabama in Huntsville) reports on behalf of the BATSE GRB team: GRB 990123 was detected by BATSE on 1998 January 23.407594 as trigger number 7343. The event was strong and consisted of a multi-peaked temporal structure lasting >100 s, with significant spectral evolution. The T50 and T90 durations are 29.82 (-/+ 0.10) s and 63.30 (-/+ 0.26) s, respectively. The burst's peak flux (50-300 keV; integrated over 1.024 s) and fluence (>20 keV) are 16.42 (-/+ 0.12) photons cmE-2 sE-1 and 5.09 (-/+ 0.02) x 10E-4 erg cmE-2, respectively---ranking it in the top 2% (0.3%) of the BATSE burst flux (fluence) distribution. The average spectral hardness of the burst, as estimated by the ratio of 100-300 keV counts to those in the 50-100 keV range, is H32 = 1.51 (-/+ 0.004), which is average among BATSE bursts. The BATSE burst location is consistent with those measured by BeppoSAX (GCN 199,202,203) and with the proposed optical/radio transient counterpart (GCN 201; 204-221). A location sky-map and lightcurve for this event (and other notable bursts) are available at the BATSE Rapid Burst Response world-wide-web site: http://www.batse.msfc.nasa.gov/~kippen/batserbr/ -eof- //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 225 SUBJECT: GRB 990123, Addendum to GCN 223 DATE: 99/01/25 23:21:07 GMT FROM: Andrew S. Fruchter at STScI This GCN is an addendum to GCN 223: Please note that Hjorth et al., GCN 219, do not indicate the position angle of the slit they used. Furthermore, to the eye, the OT appears offset to the south of the apparent host in the finding chart of Odewahn et al. (GCN 201, see also Gal et al., GCN 213), while the Keck slit lay in the E-W direction. Thus the apparent non-detection by Keck of an object reported in the NOT spectrum may be due to different position angles having been used in the observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 226 SUBJECT: GRB 990123 Optical Follow-Up DATE: 99/01/26 01:01:29 GMT FROM: Jin Zhu at Beijing Obs GRB 990123 Optical Follow-Up J. Zhu, J. S. Chen, and H. T. Zhang, on behalf of the Beijing Astronomical Observatory GRB team report: "We observed the GRB 990123 OT (GCN #202) around Jan. 25.9 with BAO 0.6-m Schmidt telescope under good weather. One 40-min. exposure was made with BATC band-i filter and the very weak source at RA=15:25:30.35, Dec=44:45:59.4 (J2000) was detected near the detection limit of the image which gives a magnitude of 21.3 +/- 0.3 (Jan 25.901) using the No. 1 and No. 2 stars in GCN #204. Assuming a minimum decay slope of 1.18 (for the OT) obtained from our previous observations (GCN #217), we conclude that the source we detect here is probably the coincident galaxy found on the digital POSS-II image by Odewahn et al. (GCN #201 and IAUC 7094). This report may be cited." //////////////////////////////////////////////////////////////////////// Circular No. 7098 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A. IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions) BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science) URL http://cfa-www.harvard.edu/iau/cbat.html ISSN 0081-0304 Phone 617-495-7244/7440/7444 (for emergency use only) GRB 990123 W. Offutt, Cloudcroft, NM, obtained two 600-s and two 900-s exposures of the optical candidate for GRB 990123, using a 0.60-m f/7 Ritchey-Chretien reflector (+ CCD + Bessell R-band filter). The mean position from the four exposures is R.A. = 15h25m30s.35, Decl. = +44o45'59".2 (equinox 2000.0; twelve USNO SA2.0 stars as reference). The following photometry (mean residual 0.25 mag) is based on the reference star located about 11".4 west of the target object (R = 19.1): Jan. 24.4400 UT, 19.8; 24.4567, 19.8; 24.4666, 20.0; 24.4781, 20.3. B. A. Skiff, Lowell Observatory, writes, in reference to IAUC 7096: "In the absence of a proper calibration sequence, optical observers of GRB 990123 have been making photometric zero-point adjustments using USNO A2.0 magnitudes. It is perhaps worth noting that these data do not in general correspond to either the Johnson B or Cousins R systems, and that they often possess substantial systematic errors in scale, in the zero-point, and as a function of star color. For the GSPC sequence near the center of the relevant plate, plus a few other stars from the Minnesota APS group (http://isis.spa.umn.edu/Docs/get_photom.html), it turns out that the A2.0 'mb' values are close to standard B; 'mr' is offset about +0.3 mag from Cousins R (A2.0 being too faint). More typically, both 'mb' and 'mr' are about 0.6 mag too bright compared to B and R. My large file of faint photometric reference stars can be used to make local corrections to A2.0 or other catalogues of faint stars: ftp://ftp.lowell.edu/pub/bas/starcats/loneos.stds." (C) Copyright 1999 CBAT 1999 January 25 (7098) Daniel W. E. Green //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 227 SUBJECT: "GRB 990123: New BV Observations" DATE: 99/01/26 02:30:05 GMT FROM: Ram Sagar at UPSO R.Sagar, A.K. Pandey, R.K.S. Yadav, Nilakshi and V. Mohan of U.P. State Observatory, Manora Peak, Nainital, India report: "We have observed the optical transient (GCN #201) of GRB 990123 (GCN #199) with the 104-cm telescope of the U.P. State Observatory, Manora Peak, Nainital, India in Johnson B and Cousin R photometric passband under good photometric sky conditions. We have calibrated the images using photometric standards located in the field of open star cluster M67. In each filter three images of 20 minutes are obtained and they are stcked to improve signal to noise ratio of the optical transient. We obtain the following magnitudes: UT date filter mag err Jan 24.90 R 21.25 0.1 Jan 24.99 B 22.05 0.2 The (B-R) colour of the OT becomes redder by about 0.2 mag compared to our observations on Jan 23, 1999 (GCN #218).These results are preliminary and more accurate results will be published later. At the Web site http://www.rri.res.in/grb990123/ all the images taken on the nights of Jan 23 and 24 are available. We have also taken images during the night of 25/26 Jan 99 and will report the results later. Sky conditions were good for photometric observations on the nights of 24/25 Jan 99 and 25/26 Jan 99 and we have observed the M67 field for calibration purposes. Precise determination of the BVRI magnitudes of the stars as well as of the OT in the field of the GRB990123 are in progress. This message may be cited." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 228 SUBJECT: GRB990123, ASCA X-ray observation of afterglow DATE: 99/01/26 15:17:19 GMT FROM: Toshio Murikami at ISAS T. Murakami, M. Ishida and T. Dotani, Institute of Space and Astronautical Science, and A. Yoshida and N. Kawai, Institute of Physical and Chemical Research, report: The X-ray astronomy satellite ASCA has been observing the X-ray afterglow of GRB990123 since January 25.688 (UT). The observation started about 55 hours after the burst, but the X-ray afterglow is still bright. ASCA will continue observing the source until January 26.806 (UT). With only one forth of the dataset down-linked at the tracking station, the flux is about 1 x 10E-12 erg cmE-2 sE-1 in 2 to 10 keV assuming a power-law with the photon index of -1.6. //////////////////////////////////////////////////////////////////////// Circular No. 7099 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A. IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions) BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science) URL http://cfa-www.harvard.edu/iau/cbat.html ISSN 0081-0304 Phone 617-495-7244/7440/7444 (for emergency use only) GRB 990123 J. Heise, Space Research Organization of the Netherlands, Utrecht; C. DeLibero, M. R. Daniele, and G. Scotti, BeppoSAX Operation Control Center, Telespazio, Rome; D. Ricci and M. Capalbi, BeppoSAX Science Data Center, Rome; L. A. Antonelli, Osservatorio Astronomico, Rome; and E. Costa, Istituto di Astrofisica Spaziale, CNR, Rome, report: "The BeppoSAX Wide Field Camera (WFC) error box of GRB 990123 (IAUC 7095) was observed from Jan. 23.65 UT (6 hr after the gamma-ray trigger) until about Jan. 24.75, using the Narrow Field Instruments of BeppoSAX. A bright, previously unknown x-ray source designated as 1SAX J1525.5+4446, was detected by the LECS and MECS units at R.A. = 15h25m31s, Decl. = +44o46'.3 (equinox 2000.0), with an error-circle radius of 50". The new source is within the WFC error circle and at a distance of 22" from the optical transient reported on IAUC 7094. The intensity of the source at 2-10 keV in the MECS at the start of the observation is 0.14 count/s, corresponding to 1.1 x 10E-11 erg cmE-2 sE-1. The source fades by an order of magnitude in 24 hr, consistent with a decay in time with a power-law index of -1.35. The average featureless spectrum has a photon power-law index of about 2, with an interstellar absorption column of 1.2 x 10E21 cmE-2, above the galactic absorption of 2.1 x 10E20 cmE-2 expected in that direction. We conclude that we have observed the x-ray afterglow of GRB 990123. It is the brightest of all gamma-ray- burst x-ray afterglows observed until now." A. Maury, Observatoire de la Cote d'Azur, Caussols; and M. Boer and S. Chaty, Centre d'Etude Spatiale des Rayonnements, Toulouse, France, report: "We clearly detected the optical candidate for GRB 990123 and its presumed host galaxy with the Observatoire de la Cote d'Azur 0.9-m Schmidt telescope, in a series of 300-s unfiltered frames. The unfiltered magnitudes (mean uncertainty 0.4 mag; USNO A2.0 reference stars) correspond approximately to R magnitudes, given the detector response: Jan. 24.03703 UT, 19.6; 24.05241, 19.6; 24.05723, 20.0; 24.06188, 19.8; 24.06653, 19.7; 24.07119, 19.4; 24.07584, 20.4; 24.08049, 19.9; 24.08515, 20.1; 24.09445, 20.3; 24.09910, 20.2; 24.11306, 19.7; 24.11773, 19.8; 24.12237, 20.2; 24.12702, 20.5; 24.13167, 20.3; 24.13633, 20.5; 24.14098, 20.2; 24.14563, 20.0; 24.15028, 20.1; 24.15494, 20.4; 24.15959, 20.4; 24.16424, 20.0; 24.16890, 20.1; 24.17820, 20.2; 24.18285, 20.1; 24.20107, 20.4. The resulting decay slope, 1.35, is in good agreement with the slope mentioned by Bloom et al. (GCN 208), given the uncertainties." (C) Copyright 1999 CBAT 1999 January 26 (7099) Daniel W. E. Green //////////////////////////////////////////////////////////////////////// Circular No. 7100 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A. IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions) BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science) URL http://cfa-www.harvard.edu/iau/cbat.html ISSN 0081-0304 Phone 617-495-7244/7440/7444 (for emergency use only) GRB 990123 C. W. Akerlof and T. A. McKay, University of Michigan, report on behalf of the ROTSE collaboration (Michigan/Los Alamos National Laboratory/Lawrence Livermore National Laboratory): "We observed the error box of GRB 990123 provided by the BACODINE Burst Position Notice (dated 23-Jan-99 09:46:59) using the ROTSE-I telephoto camera array located at Los Alamos. The first exposure began at 9h47m18s.30 UT (Jan. 23.407851), or 22.18 s after the nominal burst trigger time. A rapidly fading object was discovered at R.A. = 15h25m30s.1, Decl. = +44o46'00" (equinox 2000.0), which is within one-third of a pixel of the optical counterpart reported by Odewahn et al. (IAUC 7094). The lightcurve for this object is relatively complex: the luminosity increases by 3 magnitudes between the first and second exposures. Exposure times and estimated V magnitudes for the first six exposures are as follows: Jan. 23.407851, 5 s, 11.82; 23.408142, 5, 8.95; 23.408435, 5, 10.08; 23.410851, 75, 13.22; 23.412764, 75, 14.00; 23.414677, 75, 14.53. Note that the ROTSE-I detector system uses an unfiltered broadband CCD, so that magnitude estimates are based on comparisons to catalogue values for nearby stars. Sky-patrol images of the same coordinates taken 133 min earlier showed no evidence of the transient to a limit of at least 2 mag deeper. A more extensive analysis of these data will be available in the near future. The discovery images are posted on the ROTSE Web page at: http://www.umich.edu/~rotse/gifs/grb990123/990123.gif." J. Zhu, J. S. Chen, and H. T. Zhang, Beijing Astronomical Observatory (BAO), report that an observation on Jan. 24.730-24.861 UT with the BAO 0.6-m Schmidt telescope under nonphotometric conditions (two 60-min images taken with a BATC i-band filter; central wavelength 666.0 nm, bandwidth 48.0 nm) gives a magnitude of 21.0 +/- 0.3 (Jan. 24.818) for the transient + presumed host galaxy, using stars 1 and 2 from GCN 204 (http://gcn.gsfc.nasa.gov/gcn/gcn3/204.gcn3). No visual separation between the optical transient and host galaxy could be recognized because of the low S/N ratio and bad spatial resolution (1 pixel = 1".7; seeing 5".6). The CCD image is available at http://vega.bac.pku.edu.cn/~zj/grb/grb990123.html. A 40-min exposure on Jan. 25.901 yields a magnitude of 21.3 +/- 0.3 (near the detection limit), suggesting that by this time they were only detecting the the coincident galaxy that was found on the digital sky-survey image by Odewahn et al. (IAUC 7094). (C) Copyright 1999 CBAT 1999 January 26 (7100) Daniel W. E. Green //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 229 SUBJECT: GRB990123: NIR Observation DATE: 99/01/26 19:56:17 GMT FROM: Angelo Antonelli at Obs. Astro. di Roma L.A. Antonelli, A. Di Paola, Osservatorio Astronomico di Roma, G. Gandolfi (BeppoSAX Scientific Operation Center) report on behalf of SWIRT Team and BeppoSAX Team: "On 25.16 (UT) January 1999, we imaged the Optical Transient field in the K band using the 1.1m AZT-24 telescope and the near-infrared camera/spectrometer SWIRCAM at the Campo Imperatore Astronomical Observatory (http://www.mporzio.astro.it/cimperatore/WWW/) operated by the Astronomical Observatory of Rome (O.A.R.). The 4'X4' field of view was exposed for 3300 s reaching the limiting magnitude in the K band of 17.9 +/- 0.2 mag. No source has been found within the errorbox of the O.T. (IAUC 7094). This observation provides a more compelling upper limit in K band with respect to the previous observation in the same band (GCN #214). The behaviour of the source between the two observation, at this wavelenght, is unknown. Further near infrared observations are in progress. This message may be cited." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 230 SUBJECT: GRB 990123: Strong MeV CGRO-COMPTEL detection now posted on WWW DATE: 99/01/26 22:15:07 GMT FROM: Alanna Connors at UNH A. Connors and R. M. Kippen, for the CGRO-COMPTEL Rapid Burst Response collaboration; and S. Barthelmy and P. Butterworth, for BACODINE/GCN, report the following: CGRO-COMPTEL observed GRB 990123 to be extremely bright in its ~MeV energy range. The >0.7 MeV emission rose about 18 seconds after the initial BATSE trigger at 9h 46m 56.12s U.T. and lasted about 46 seconds, for a 10 sigma detection, despite its very large zenith angle (59 degrees). An initial detection notice was sent about 10 minutes after burst onset. Improved skymaps and light-curves for the full 0.2-30 MeV range have now been posted at the CGRO-COMPTEL Rapid Burst Response web-site: http://wwwgro.unh.edu/bursts These are still considered preliminary as our standard energy calibration is not yet complete. This message can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 231 SUBJECT: GRB990123, OSSE observations DATE: 99/01/27 09:57:44 GMT FROM: Steven M. Matz at Northwestern U/OSSE S. M. Matz (Northwestern University), G. H. Share, R. Murphy, and J. D. Kurfess (Naval Research Lab) report on behalf of the OSSE team: The OSSE instrument on board the Compton Gamma-Ray Observatory detected strong emission from GRB 990123 in its central detectors and in its active NaI shields. While the burst was not in the detectors' field of view, it was still detected to >3 MeV in two 16 s intervals. The rise and first strong peak (at about trigger+25 s) are roughly (within 1--2 s) aligned at all energies. The low-energy (<100 keV) burst emission appears to last significantly longer than the higher energy emission. Detailed spectral analysis is underway; preliminary analysis indicates that the average spectrum of the main burst can be well described above 0.8 MeV by a photon power law with an index of about -3. Time histories from the OSSE central detectors in different energy ranges from 50 keV to >3 MeV are posted on the OSSE burst web page ( http://www.astro.nwu.edu/astro/osse/bursts/ ) along with a preliminary spectrum of the burst. Also available are a plot and raw data for the high time resolution (16 ms) history of the first 60 s of the burst from the triggered OSSE shield data (>100 keV). This report may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 232 SUBJECT: GRB 990123: near-infrared observations. DATE: 99/01/27 14:51:12 GMT FROM: Angelo Antonelli at Obs. Astro. di Roma L.A. Antonelli, A. Di Paola, R.Speziali, Osservatorio Astronomico di Roma, Italy, and G. Gandolfi, BeppoSAX Scientific Operation Center, Italy, report on behalf of SWIRT Team and BeppoSAX Team: "We observed the Optical Transient field of GRB 990123 in the J band using the 1.1m AZT-24 telescope and the near-infrared camera/spectrometer SWIRCAM at the Campo Imperatore Astronomical Observatory operated by the Astronomical Observatory of Rome (O.A.R.). On 25.22 (UT) January 1999, the OT field was observed for a total exposure time of 2000 s reaching the limiting magnitude in the J band of 19.5 +/- 0.3 mag . On 26.12 (UT) January 1999 the field was re-observed for a total exposure time of 3600 s reaching the limiting magnitude in the J band of 19.3 +/- 0.3 mag. No source has been found in both observations within the errorbox of the O.T. (IAUC 7094). These observations provide an upper limit, in the J band, to the infrared counterpart (if any) of GRB 990123 and on its behaviour. This message may be cited." [GCN OP NOTE (99/01/27 15:10 UT): Some of you on the GCN Circulars list probably received this Circular twice. Due to a very low probability occurance of e-mail deliver deamons timing, this notice got deposited in the "import" queue of the Circulars processing deamon twice.] //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 233 SUBJECT: GRB990123, Optical BVRI Observations DATE: 99/01/27 19:24:25 GMT FROM: Elena Pian at ITESRE-CNR,Bologna GRB 990123 BVRI Photometry N. Masetti, E. Palazzi, E. Pian, F. Frontera (ITESRE-CNR, Bologna), C. Bartolini, A. Guarnieri, A. Piccioni (Astronomy Dept., Univ. Bologna), G. Valentini (Teramo Astr. Obs.) and E. Costa (IAS-CNR) report: "We have imaged the field of GRB990123 with the Bologna Astronomical Observatory 1.5m telescope equipped with BFOSC, using Johnson B and V, and Cousins R and I filters in January 24-26. Calibrations were done referring to GCN 206 for the B image, to GCN 204 for the R image, and using the standard star BD+252534 (Taylor et al. 1989, AJ 97, 1798) for the V and I images. In the appended table the preliminary magnitudes of the optical transient (GCN 201) are reported along with the observation dates. Power-law fits to the R and V band data yield temporal decay indices of alpha = 1.20 +- 0.08 and alpha = 1.25 +- 0.16, respectively (errors are 1 sigma), with satisfactory chi square values. No indication is found of a flattening of the light curve due to an underlying galaxy. Suggestion of a slight flux increase is seen on January 25 in both R and V bands, as opposed to the overall fading trend. This is however not significant. The BVRI spectral continuum of the optical transient in the first night (average time of Jan 24.16), dereddened with E(B-V) = 0.016 (GCN 207), has a power-law shape (f_nu = k*nu^{-beta}) with best-fit slope beta = 1.1 +- 0.2 (1 sigma). The BVRI light curves and the radio-to-X-ray spectral energy distribution of the transient are also shown at the Web site http://tonno.tesre.bo.cnr.it/~masetti/grb990123.html Multiwavelength observations, particularly in the near-infrared and millimetric bands, are needed and urged. Date (UT) mag error band ----------------------------------- 1998 Jan 24.122 19.36 0.20 I 24.142 19.79 0.10 R 24.164 19.97 0.16 V 24.194 20.64 0.07 B 24.216 19.92 0.10 R 25.138 20.91 0.10 R 25.159 20.77 0.10 R 25.181 21.01 0.20 V 25.203 20.93 0.20 V 26.154 21.77 0.16 V 26.154 21.56 0.10 R This message can be cited." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 234 SUBJECT: Search for Potential Images of GRB 990123 DATE: 99/01/27 20:27:44 GMT FROM: Robert Rutledge at Caltech Search for Potential Images of GRB 990123 R. Rutledge and S. R. Kulkarni (CIT) note: Djorgovski et al. (GCN #216) have suggested that GRB 990123 is lensed by a foreground galaxy identified by Odewahn et al. (GCN #201) and presumed to be at redshift 0.21 or 0.28 (Hjorth et al. GCN #219). The basis of this argument is two fold: (1) the energetics of the GRB are reduced, as lensing would provide strong amplification, and (2) the foreground galaxy, due to its placement and likely mass, must result in some amount of lensing of a background object at the position of the optical transient. A consequence of this lensing hypothesis is image splitting. The same burst would arrive at different times, with the time difference proportional to the image separation (e.g., Turner et al. GCN #221). Motivated by these considerations we have looked into the BATSE catalog to see if there are GRBs in the general vicinity of the location of GRB 990123 (Piro et al, GCN #199) and with close to identical profile. The two profiles need not be exactly identical since microlensing combined with source expansion can lead to changes in profile. Within a 4-sigma error radius consistent with the GRB 990123 OT transient position, we find two double-peaked GRBs. In one of these (GRB 970627, BATSE Trigger #6279), the peaks are similar in separation and peak-width ratio to GRB 990123, although the peak intensity ratio is different by about 60+/-20%. In addition, there is excess emission in GRB 990123 following the two peaks, which is not observed from GRB 970627. However, based on the characteristics of intensity profiles, it is possible that GRB 970627 and GRB 990123 are lensed images of the same GRB event. We estimate that the chance probability of a similar profile GRB being consistent in position is about 2%, based on the identification of 8 similar GRB intensity profiles among the approximately 2000 GRBs in the BATSE catalog. If we include in this statistic GRBs with a more dissimilar intensity profile, the chance probability increases. We find 24 double-peaked GRBs (of 2000 in the BATSE Catalog) which are comparable in peak separation (15-25 seconds) but are still dissimilar to GRB 990123, resulting in a chance probability of 6.4%. A comparison between the light curves of these two GRBs is available at http://www.srl.caltech.edu/personnel/rutledge/0123/bursts.html. If GRB 970627 is indeed a lensed image of GRB 990123, then to explain the very long time delay between the two images (1.5 years), the positional splitting must be several arcseconds in size and would most certainly require multiple lenses or a cluster. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 235 SUBJECT: Search for Potential Images of GRB 990123 DATE: 99/01/27 21:46:09 GMT FROM: Kevin Hurley at UCBerkeley/SSL K. Hurley, UC Berkeley Space Sciences Laboratory, on behalf of the Ulysses GRB team, and C. Kouveliotou, Universities Space Research Association, Marshall Space Flight Center, on behalf of the BATSE team, report: GRB 970627 (=BATSE Trigger #6279), suggested as a possible gravitationally lensed counterpart to GRB 990123 (Rutledge and Kulkarni, GCN 234), was detected by the Ulysses GRB instrument and triangulated to an annulus centered at RA(2000)=153.491, Decl.(2000)=26.188, with radius 67.841 degrees and 3 sigma width 0.065 degrees. This annulus intersects the one for GRB 990123 (GCN 222) at two locations: around RA(2000)=84.055 degrees, Decl.(2000)=+08.531 degrees, and around RA(2000)=234.866 degrees, Decl.(2000)=+37.878 degrees. Neither error box, nor the annulus for GRB 970627, includes the optical transient (GCN 206). (We note that the IPN annulus and the BATSE error circle for GRB 970627 do not intersect, nor does the BATSE error circle include the optical transient, but this is not unexpected, given that the error circle is a 1 sigma location.) We conclude that GRB 970627 is not the lensed counterpart of GRB 990123. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 236 SUBJECT: On the Lensing Interpretation of GRB 990123 DATE: 99/01/28 10:49:17 GMT FROM: Shude Mao at MPI,Garching Shude Mao (Max Planck Inst. for Astrophysics) reports: Djorgovski et al. (GCN Circ. 216) suggested that GRB 990123 might be highly magnified (A>10) by an intervening galaxy based on a variety of arguments. A likely scenario is that the bursting source is very close to a fold caustic. As a result, we have a PAIR of highly magnified images (we call B2 and B3) plus other additional image(s). If this scenario is correct, then from the lensing theory, three points can be immediately made: 1. There must be a fainter burst that has arrived before GRB 990123. This first burst (we call B1) would be offset from GRB 990123 by about ~2". This expectation is valid no matter what the lens potential. Notice that, in this scenario, all the optical and radio afterglows we see now are the sum of the first-arriving burst B1 and GRB 990123. High resolution imaging in the radio and in the optical (with HST) may reveal the presence of B1. The time interval and intensity ratio between B1 and GRB 990123 does depend on the model. A rough estimate of the time delay is a few days to a month, and the intensity ratio is around a few to a few tens. These predictions can be made more precise when the astrometries and velocity dispersion of the foreground galaxy are better known. The gamma-ray burst data archive should be searched to see whether there was such a burst. A fourth image (B4) much fainter than GRB 990123 may also appear after about a month. 2. The gamma-ray burst host galaxy, since it is extended, will be distorted into a ring or arcs if the center of the host galaxy does not have a significant offset from GRB 990123. Such features can be detected with HST imaging (see also Turner, GCN 221). This expectation is independent of the models. 3. The close pair of images should have roughly equal intensities. The time delay between these two images depends strongly on the magnification; a simple model shows that it can be between tens of seconds to a fraction of a day. This close pair therefore should have ALREADY left imprints on the after glow light curves. The close pair should have an image splitting of about 0.05" to a fraction of arcsecond; HST imaging will either provide a confirmation or rule out this scenario. If the time delay between the close pair can be as short as tens of seconds, this raises an intriguing possibility: is GRB 990123 itself lensed? That is, GRB 990123 may be superposed by two bursts coming from the close pair. These two bursts have a time lag of about 15 seconds, producing the first and second peaks in the light curve. It will be very interesting to check whether the gamma-ray spectrum and light curve of GRB 990123 are consistent with this superposition scenario. If this hypothesis is correct, then the close pair should have an imaging splitting of ~0.05" and each is magnified by a factor of about 100. More information (including figures) can be found at http://www.mpa-garching.mpg.de/~smao/grb.html This report may be cited. [GCN OP NOTE: This Circular was received at 09:19 UT, but was delayed until an entry in the distribution list was created.] //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 237 SUBJECT: GRB 990123: Correction to GCN 230 - C.A. Young added to author list DATE: 99/01/28 21:01:26 GMT FROM: Alanna Connors at UNH The name of C. A. Young, duty scientist at the time of CGRO-COMPTEL's initial rapid (~10 minute) localization of GRB 990123, was inadvertently left off the author list. The correct attribution should be as follows: "A. Connors, R. M. Kippen and C. A. Young, for the CGRO-COMPTEL Rapid Burst Response collaboration; and S. Barthelmy and P. Butterworth, for BACODINE/GCN, report the following:" This note can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 238 SUBJECT: GRB990123, Preliminary Lens Search Results DATE: 99/01/28 21:35:38 GMT FROM: Robert Nemiroff at Michigan Tech. R. J. Nemiroff (Michigan Tech.), G. F. Marani (NRC/NASA), J. T. Bonnell (USRA/NASA), J. P. Norris (NASA/GSFC), and C. A. Meegan (NASA/MSFC) report: There is, as yet, no primary indication that GRB 990123 has undergone any type of strong gravitational lensing. Weak lensing: Most sources at z>1.6 will be either gravitationally amplified or (more likely) de-amplified by >5% by inhomogeneities in the gravitational field between the observer and the source (see, for example, Holz et al. astro-ph/9804271). Strong Lensing: Galaxy lensing: There is, as yet, no primary indication that GRB 990123 is one of multiple macro-images created by an intervening galaxy lens. In comparison with QSOs, it is not unusual for single image QSOs to be found within 3 arcseconds of a low mass galaxy (e.g. Claeskens & Surdej 1998, A&A 335, 69) or for a single image QSO to have absorption lines. As GRB 990123 was the brightest event ever detected with a measured cosmological redshift, its macrolensing probability is high relative to other GRBs and afterglows, but still, quite possibly, low in absolute terms. The foreground galaxy near GRB 990123 is intriguing but not yet defining. The "probability" now all hinges on the unknown masses and mass distributions internal to foreground galaxies. No other BATSE triggered GRB has been found that is consistent with a lensing interpretation. Twenty-three BATSE GRBS have occurred in the past three years within a 3-sigma error contour of GRB 990123. The closest two in light curve shape were judged to be BATSE triggers 6279 and 6698. A preliminary visual inspection reveals none of them is a close light-curve match to GRB 990123. Millilensing: There is, as yet, no primary indication that GRB 990123 has undergone significant amplification by a compact mass on the globular-cluster scale. The two main peaks in the GRB light curve do not appear to be co-added replicas of a single light curve seperated by major peak are significantly different (> 5 sigma, preliminary analysis) in BATSE channels 1 and 4. Similarly, the ratios in peak flux between the first major peak and the last peak are also significantly different (> 5 sigma, preliminary analysis). Microlensing: There is, as yet, no primary indication that GRB 990123 has undergone significant light curve distortion due to microlensing by compact masses on the stellar mass scale. Microlensing at low optical depths would create images separated in time by only microseconds (Nemiroff 1994, ApJ 432, 478; Nemiroff 1998, ApJ 494, L173) to milliseconds (Williams & Wijers 1997, MNRAS 286, L11), generally below minimum time scale of BATSE GRB resolution (64-ms). We encourage, however, continued attempts to recover secondary images from any GRB or afterglow, including GRB 990123. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 239 SUBJECT: GRB 990123: Continued Radio Observations DATE: 99/01/29 04:22:52 GMT FROM: Shri Kulkarni at Caltech S. R. Kulkarni (Caltech) and D. A. Frail (NRAO) report on behalf of the Caltech-NRAO-CARA gamma-ray burst collaboration the following. "We have continued monitoring the error box of GRB 990123 (GCN #202) with the Very Large Array (VLA). All our observations were conducted in the 8.46-GHz band. At the position of the optical transient we obtain the following fluxes: Here is a summary of all the X-band observations to date. Jan 23: <68 microJy (GCN #200) Jan 24: 260 microJy (GCN #211) Jan 26: <78 microJy Jan 27: <50 microJy Jan 28: <50 microJy Note: The upper limits are indicated by "<" and are 2-sigma. To summarize, the radio afterglow has been detected only once, on January 24 1999. The detection was very secure being 8-sigma. The source was seen in both intermediate frequency (IF) bands and in both senses of polarization (R and L). In contrast, the average of the flux for the period January 26-28 is <32 microJy. This high degree of variability could be due to interstellar scattering and scintillation (ISS). However, the factor of 10 variation in the flux density requires rather extreme ISS. In addition, we expect the source to be gradually rising with time. Thus the absence of the source on three successive days is quite puzzling. Discarding the ISS hypothesis, we have two choices. First, the radio emission detected on January 24 is some kind of precursor event to the main afterglow. Typically, the radio afterglow in the 8.46-GHz band rises to the peak flux in about 10-20 days. We have little data about the behavior of radio afterglow within a few days after the burst. Thus it is difficult to accept or reject this hypothesis. The alternative hypothesis is that the GRB is lensed (GCN #216). At the present time, there is no firm evidence for lensing. However, the lensing idea is economical in energetics. Likewise, the lensing hypothesis offers a simpler alternative to the curious phenomenon discussed above. As discussed by various people (S. Mao GCN#236, R. Narayan, pers. comm.) a robust expectation of strong lensing is that we should first see the faint image "B1" (in the terminology of GCN #236). In this framework, we identify the radio source of Jan 24th with the radio afterglow of the B1 component. If this interpretation is correct then the radio afterglow of the brighter components B2 and B3 should become visible in in the next few weeks. We do not possess sufficient astrometric accuracy to see if the reported (GCN #201) optical afterglow (which is presumably due to B1+B2) and the radio afterglow are offset on the sky. Indeed, the excellent agreement (0.5 arcsec) between the positions of the optical and the radio afterglow places a limit of a delay of 30 days between components B1 and B2+B3. Clearly, radio monitoring will refute or confirm this hypothesis. This report is citeable." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 240 SUBJECT: GRB 990123: Detection of the IR Transient, and the Light Curve Fits DATE: 99/01/29 04:31:21 GMT FROM: George Djorgovski at Caltech/Palomar GRB 990123: Detection of the IR Transient, and the Light Curve Fits J. S. Bloom, C. Koresko, S. R. Kulkarni, S. G. Djorgovski, R. R. Gal, and S. C. Odewahn, Caltech, H. I. Teplitz, NASA Goddard Space Flight Center, D. Koerner, Univ. of Pennsylvania, D. Kirkpatrick, Infrared Processing and Analysis Center, M. A. Malkan, and I. S. McLean, Univ. of California, LA, D. A. Frail, National Radio Astronomy Observatory, report on behalf of the Caltech-CARA-NRAO GRB collaboration: "The field of the optical transient of GRB 990123 (GCN 201) was observed with the Near Infra-red Camera (NIRC) on the Keck I telescope on 24 January 1999 UT by Koerner and Kirkpatrick. We report the discovery of the IR counterpart of the afterglow with K = 18.3 +/- 0.03 mag (epoch 24.6356 Jan 1999 UT). The same field was observed by Malkan, Teplitz and McLean on the nights of January 27.65 and 28.55 UT, and in both instances the object was readily detected. Fitting a power law to the three magnitudes yields a power law exponent of alpha_K= -1.14 +/- 0.08. Separately, we have carried out a program of recalibrating Gunn r and R band magnitudes reported by others via the GCN. We used those measurements which reported the magnitude of a reference star (or stars) and have put all the measurements on a common photometric system. A fit to these recalibrated magnitudes yields a power law slope, alpha_r = -1.13 +/- 0.03. Within errors, the slope of the K band data is fully consistent with that obtained from the r/R band data. We adopt a mean alpha of -1.13. The color difference between the decaying r and K fluxes is (r-K) = 2.75 mag. Converting the magnitudes to flux this color difference corresponds to beta = -0.82, where f_nu = const * nu^beta. The ratio alpha/beta = 1.38. This suggests that the cooling frequency is higher than the central frequency of the r band (about 4x10^14 Hz) even two days after the burst. We urge continued monitoring of the optical transient in the r/R band with the view of detecting the passage of the cooling break. In contrast to the light curves measured in the r and K bands, the light curve in the B band (calibrated on a uniform photometric system) is not well described by a power law. The origin of this discrepancy is as yet unclear. Further observations are in progress. This report is citeable." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 241 SUBJECT: GRB990123, Probability of gravitational lensing DATE: 99/01/31 02:31:33 GMT FROM: Brad Schaefer at Yale U Bradley E. Schaefer (Yale): In the last few days, the GCN has had several discussions about the possibility that GRB990123 might be lensed with a high amplification. This note is to provide balance and point out several problems with this possibility. In particular, the arguments suggest that there will be no repeat lens events on short (or long) time scales. (1) The idea of GRB990123 lensing has weak motivation. The motivation that GRB990123 is lensed is (A) to reduce the deduced isotropic-equivalent energy (2.3x10^54 erg) to a level that can be readily explained by models, (B) to account for the lack of previous optical flash detection by LOTIS and ROTSE [GCN #216], (C) to account for GRB970627 as a lensed image [GCN #234], and (D) to explain the large radio variability [GCN #239]. (A) To claim that GRB990123 is too energetic requires a knowledge of the burst energy budget, whereas no such answer is known. Nevertheless, within current reasonable models (e.g., collapsars, merging compact objects) the typical gamma ray energies range up to ~10^52 ergs. [This forces the lens amplification, A, to be >200 or so.] Any such argument would already require that GRB971214 [3x10^53 erg; Kulkarni et al. 1998, Nature, 393, 35] and GRB980703 [2x10^53 erg; GCN #139, GCN #143] must also be lensed with large amplitude. The likelihood of three high amplitude lenses among the 17 SAX bursts is close to zero. (B) The optical flash luminosity is indeed large [it would appear brighter than our Sun at a distance of 1 kpc], but we have no idea of what is expected, so with A=200 the source still has M~-30.7 and this is still astounding. More to the point, no previous search would have detected an optical flash with the E_gamma/E_opt ratio for GRB990123 (i.e., V~9 [GCN #205] for a gamma ray fluence of 5.1x10^-4 erg cm^-2 [GCN #224]). For example, the highest fluence event seen by GROCSE is 1.9x10^-5 erg cm^-2 with an optical limit of 8.1 mag [H. S. Park et al. 1997, ApJ, 490, 99]. For LOTIS, the strictest limit comes from GRB970223 with a fluence of 4.8x10^-5 erg cm^-2 and an optical limit of 11.0 mag [H. S. Park et al. 1997, ApJLett, 490, L21]. So there are no missing-optical-flashes to motivate a lens suggestion. (C) For GRB970627 to be a lensed image, it must have the same light curve, spectrum, and position as GRB990123. [Microlensing could conceivably make mild changes in the light curve or spectrum by imaging different portions of the fireball, but then the time delay between images cannot be 1.5 years without simultaneously invoking high amplitude microlensing on top of high amplitude macrolensing.] The two bursts have peak-to-peak times of 12s and 17s, have greatly different peak intensity ratios, have greatly different peak shapes, and GRB970627 lacks the late time flux prominent in GRB990123. The two bursts have greatly different hardness ratio in BATSE channels 1, 2, and 3, with H21 equal 1.37 versus 0.56 and H32 equal 5.83 versus 1.14 [http://www.batse.msfc.nasa.gov/data/grb/catalog/flux.html]. The GRB990123 OT position is 4.23 degrees away from the IPN annulus for GRB970627 which has a 3-sigma width of 0.065 degrees [GCN #235]. Thus, GRB970627 is certainly not a lensed image of GRB990123. (D) The radio observations of GRB990123 to date show >10X variations in flux [GCN #239], but this is not qualitatively different from the 4X variations already known from GRB scintillation [e.g., Frail et al. 1997, Nature, 389, 261]. Nevertheless, GCN #239 suggests that normal variation of a GRB cannot account for this variation, and instead propose that the radio detection is of an earlier lensed image of the same GRB. However, this alternative suggestion has exactly the same problem as what it was trying to replace, since then the earlier lensed image is required to vary by >10X. That is, lensing does not solve the posed problem. So logically, there is no motivation to invoke lensing. (2) A GRB990123 lensing event is now extremely improbable. Within the lensing hypothesis, for simple lenses, the time delay between images will scale as the mass of the lens, with typical delays of 250 seconds for a 10^9 solar mass lens or 7 hours for a 10^11 solar mass lens [see E. Turner et al. 1984, ApJ, 284, 1]. So for the simple case, there can be no lensed event in the future. For more complex lenses, GCN #236 points out that the time delay between the two brightest and roughly equal images will be from tens of seconds to a fraction of a day. In either case, the lack of a comparable sized lens argues strongly that there will be no more images arriving in the future and that there has been no lensing at all. The fraction of quasars that are lensed with moderate amplification is ~10^-3. The fraction of GRBs with multiple images is <10^-3 (G. Marani 1998, Thesis, George Mason). For a GRB distance of z=1.6, the expected lensing fraction is ~2x10^-3 (D. Holz et al. 1999, ApJ, 510, 54). [A correction for amplification bias is needed for this theoretical estimate, but this will not be large due to the turn over in the LogN-LogP curve.] So, for GRBs with A>~2 we expect the lensing fraction to be ~10^-3. The lensing probability scales as A^-2. For the 17 SAX bursts, we then expect a final probability of <2x10^-6 that any burst will be amplified as much as required. This probability calculation suggests strongly that GRB990123 is not lensed and thus will not have future lensing events on short or long time scales. (3) Beaming is a better model. Observationally, we know that the burst emission is collimated (to allow the escape of GeV photons) and that most of burst emission is coming from very small angular beams (e.g., B. Schaefer & K. C. Walker 1998, ApJLett, 511, in press; ASTRO-PH/9810271; ASTRO-PH/9802200). Theoretically, recent models produce small cones of emission, for example S. Woosley suggests a beaming factor of 0.015 while M. Rees suggests it can be as low as 10^-4 [Rome GRB Conf.]. So we have every reason to expect significant beaming factors. This expectation will immediately lower the burst energy requirements and eliminate the motivation for a GRB990123 lens. Why invoke an extremely improbable solution with no positive evidence when everyone already knows that beaming solves the problem and must be present. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 242 SUBJECT: GRB990123 Optical Observations DATE: 99/02/01 02:19:38 GMT FROM: Jules Halpern at Columbia U. I. A. Yadigaroglu, J. P. Halpern, R. Uglesich, & J. Kemp (Columbia U.) report on behalf of the MDM Observatory GRB follow-up team: "We imaged the field of GRB 990123 in the R band on Jan. 30.52 using the MDM Observatory 2.4m telescope. A total of 40 minutes exposure was obtained in seeing of 0.9-1.0 arcsec. The optical transient is clearly detected at magnitude R = 23.01 +/- 0.24 (referenced to the comparison star of GCN #207, assuming r - R = 0.4). An independent calibration using a Landolt standard also gives a consistent magnitude. The OT position, measured with respect to the USNO-A2.0 reference system, is (J2000) RA 15:25:30.34, Dec +44:45:59.2 with an uncertainty of 0.3 arcseconds in radius. This position is consistent with that of the original detection of the OT (GCN #206). The temporal power-law decay slope connecting our observation to the first Palomar detection is alpha_r = -1.15 +/- 0.07, consistent with all previous observations, which gave alpha_r = -1.13 +/- 0.03 (GCN #240). Thus, the OT appears to be unresolved, at a fixed position, and following a power-law decay in time. However, we see no object corresponding to a suggested intervening galaxy that was estimated to lie 1.8 arcsec north of the OT (GCN #206). In fact, there is no other object on our image within 5 arcsec of the OT, to a limiting magnitude of approximately R = 24. Since this galaxy was only reported to be seen marginally on one POSS II red plate with R = 21.5 +/- 0.5 (GCN #213), we conclude that it probably does not exist. If true, this eliminates one of the arguments for hypothesizing that the burst is lensed." The MDM image will be posted in the near future at http://cba.phys.columbia.edu/grb/ This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 243 SUBJECT: GRB 990123: New Constraints on Possible Foreground Galaxies DATE: 99/02/01 15:21:54 GMT FROM: George Djorgovski at Caltech/Palomar GRB 990123: New Constraints on Possible Foreground Galaxies S. G. Djorgovski, S. R. Kulkarni, J. S. Bloom, C. Koresko, R. R. Gal, S. C. Odewahn (Caltech), M. A. Malkan, I. S. McLean (UCLA), H. I. Teplitz (GSFC), D. Koerner (U. Penn.), D. Kirkpatrick (IPAC), and D. A. Frail (NRAO), report on behalf of the Caltech-UC-NRAO-CARA GRB collaboration: We performed a new differential astrometry between the Palomar discovery images of the optical transient (OT) associated with GRB 990123 (GCN 201, GCN 205) and the DPOSS F (red) plate containing the field. The results indicate that the apparent foreground galaxy near the OT position (GCN 201, GCN 206, GCN 207) is offset by 2.4 arcsec to the N and 1.0 arcsec to the E of the OT, with the estimated errors of 0.13 arcsec (systematic) + 0.3 arcsec (random) in each coordinate. As we noted before, at R ~ 21.5 mag this object corresponds to approximately 2-sigma detection on the plate scan. We detect no objects down to a limiting magnitude K ~ 23 in this location in the stack of deep K-band images obtained at the Keck-I telescope on 24 and 27 January 1999 UT (GCN 240). The implied limiting color is so blue that we can exclude even the most actively star-forming galaxies. We thus conclude that the sky survey detection was spurious. This is in a complete agreement with the findings by Yadigaroglu et al. (GCN 242) in the R band. This leaves open the question of the identification of galaxies responsible for the absorption systems at z = 0.286 and z = 0.210 reported by Hjorth et al. (GCN 219), as well as the z = 1.60 absorption system itself (Kelson et al., IAUC 7096; and GCN 219). Using the best-fit R-band light curve power-law slope alpha = -1.13 +/- 0.03 (GCN 208, GCN 240) normalized to the K-band detection from 24 January 1999, we estimate the maximum allowed contribution to the observed K-band light in our measurements from 27 and 28 January 1999 UT from any underlying galaxy (either the host and/or the foreground absorbers). We obtain K > 22 mag for any such objects. However, in our best-seeing (FWHM ~ 0.5 arcsec) images, from 27 January 1999 UT, we detect a faint, galaxy-like extension to the N of the OT, with an apparent center about 0.5 arcsec from the OT itself. Its rough estimated magnitude is in the range of K ~ 22 to 23 mag, in agreement with the limits derived from the light curve analysis. Pending an independent confirmation of this detection, this object may be either a foreground dwarf galaxy responsible for one of the absorption systems reported by Hjorth et al., or a highly luminous host of the GRB itself (possibly responsible for the absorption system at z=1.6). While there is no clear observational evidence for a strong gravitational lensing of this burst, the possibility remains open, and the presence of foreground galaxies along the line of sight suggests that some lensing magnification must be taking place (regardless of the extraordinary apparent energetics of this burst). Forthcoming observations from the Keck and the HST should clarify the situation. This report is citeable. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 244 SUBJECT: GRB990123, 15-GHz limits DATE: 99/02/01 22:48:20 GMT FROM: Guy Pooley at MRAO, Cambridge, UK Guy Pooley, MRAO, University of Cambridge, reports the following: Five observations of the field of GRB990123 have been made with the Ryle Telescope, Cambridge UK at 15 GHz. No significant detection was made. This is a summary: date UT S sigma -- microJy -- 990125 0120-1116 160 180 990126 0116-1140 -12 180 990129 0104-0727 -197 200 990130 0738-1122 106 420 990131 0734-1119 48 300 //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 245 SUBJECT: GRB990123, Upcoming HST Service Observations DATE: 99/02/03 15:03:58 GMT FROM: Steven Beckwith at STScI Steven Beckwith on behalf of STScI reports: Owing to world-wide interest in GRB 990123, the Space Telescope Science Institute will carry out imaging observations with the HST STIS \ CCD 50CCD (clear filter), dithered, using 3 orbits of Director's Discretionary Time as a service to the community. The observations are scheduled to start Monday, 8 February at 23:06:54 UT, and finish Tuesday, 9 February, 03:21:43 UT. In the spirit of a cooperative multiwavelength attempt to better identify and understand the nature of gamma-ray bursts, the HST data will be publicly available with no proprietary period immediately upon placement into the HST Data Archive, within a day or two of the observations. When we know the exact time of placement in the Archive, we will post it. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 246 SUBJECT: GRB 990123: Publicly available reduced HST images DATE: 99/02/03 15:47:41 GMT FROM: Andrew S. Fruchter at STScI Andrew Fruchter, on behalf of the HST GRB Collaboration, reports: As the Director of STScI, Steven Beckwith, has announced in GCN 245, service observations of GRB 990123 by HST using the STIS CCD will be released to the community immediately upon their having been processed through the standard HST data pipeline and fully ingested by the HST Archive. However, the standard data pipeline will not combine the 6 separate dither pointings, nor do a complete removal of the hot pixels and cosmic rays. Therefore, because of the great community interest in these observations, the HST GRB Collaboration (whose time begins again with Cycle 8) plans to fully reduce the data, and make the resulting FITS images publicly available to the community via the web within a day of the release of the data by the HST Archive (the wait may be significantly less, depending upon the timing of the release of the data from the archive). A GCN containing information on how to retrieve the fully reduced images will be sent as soon as they are available. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 247 SUBJECT: GRB990123, is the "radio flare" due to an inhomogeneous medium? DATE: 99/02/03 18:17:17 GMT FROM: Xiangdong Shi at UCSD Xiangdong Shi and Geza Gyuk (UC, San Diego): In GCN#211,239 S. R. Kulkarni and D. A. Frail reported radio observations of GRB990123, which show a "radio flare" on Jan. 24. GRB990123 appears otherwise to be radio-quiet as of yet (GCN#200,212,239). We suggest the possibility that this "flare" resulted from the GRB external shock running into a cloud off line-of-sight. This section of the shock was decelerated efficiently and its sychrotron frequency quickly fell into the range of radio waves. This inhomogeneity of the medium may explain the abruptness and shortness of the radio emission. The "flares" in other wavelengths were brief and might also have been buried in the main afterglow. We speculate that the cloud may have been composed of prior ejecta from the gamma-ray burst progenitor. If there are still other nearby clouds, it will be interesting to see whether the "flares" recur. One implication of this hypothesis, if it is true, is that the GRB990123 is not likely to be strongly beamed (>10). Its intrinsic energy output would in turn be indeed huge. This message is citable. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 248 SUBJECT: GRB990123, Optical observation DATE: 99/02/03 20:02:38 GMT FROM: Jules Halpern at Columbia U. I. A. Yadigaroglu & J. P. Halpern (Columbia U.) report on behalf of the MDM Observatory GRB follow-up team: "We imaged the field of GRB 990123 in the R band on Feb. 3.54 UT using the MDM Observatory 2.4m telescope. A total of 60 minutes exposure was obtained in seeing of 1.2 arcsec. An object is detected at magnitude R = 23.9 +/- 0.25 (referenced to the comparison star of GCN #207). However, its position is approximately 0.6 arcsec north of the previous position. The new position is (J2000) RA 15:25:30.343, Dec +44:45:59.86, whereas the position on Jan. 30.52 was (J2000) RA 15:25:30.330, Dec +44:45:59.27. These positions are measured with respect to the same set of comparison stars, and they each have a statistical uncertainty of 0.3 arcseconds in radius, but negligible systematic difference. A possible extension in a Jan. 27 K-band image 0.5 arcsec to the north of the OT was described by Djorgovski et al. (GCN #243). Our new R-band image is consistent with that report. The optical transient has faded at an accelerated rate since our last reported observation on Jan. 30.52 (GCN #242). A continuation of the alpha_r = -1.13 decay (Bloom et al. GCN #240) would have predicted an R magnitude of 23.47 on Feb. 3.54. Since the position of the optical centroid has shifted, we conclude that our measured R = 23.9 represents an upper limit to the magnitude of both the OT and any coincident galaxy, and that we are beginning to detect either an intervening galaxy or the host galaxy of the burst. We note that the accelerated decay of the OT could be an indication that the cooling frequency has passed below the optical band, or that a jet which initially was highly collimated toward us has begun to spread. An alternative interpretation in which the initial OT has disappeared, and at the same time been replaced by a fainter lensed component, seems less likely. The new MDM image will be posted in the near future at http://cba.phys.columbia.edu/grb/ This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 249 SUBJECT: GRB 990123 NOT Spectrum Update DATE: 99/02/03 22:46:15 GMT FROM: Jens Hjorth at U.Copenhagen GRB 990123 NOT Spectrum Update J. Hjorth (Copenhagen), M. I. Andersen (NOT), H. Pedersen (Copenhagen), M. R. Zapatero-Osorio (IAC), E. Perez (IAA) and A. J. Castro Tirado (LAEFF, IAA) report: "We have conducted an improved analysis of the NOT spectra reported in GCN #219. We detect several absorption lines in addition to the ones found in the preliminary analysis, including Al III (185.5 and 186.3 nm). The suggested assignment of two significant absorption lines with Zn II (202.6 and 206.3 nm) is uncertain. The resulting updated redshift is 1.598 +- 0.001. The detection of an emission line associated with a system at z = 0.286 is not confirmed. This considerably reduces the significance of the proposed line system at z = 0.286. The significance of the line system at z = 0.21 is unchanged and its reality remains uncertain. These findings are consistent with the Keck results (IAUC #7096; GCN #223; GCN #235). The orientation of the slit during the observations was along the parallactic angle (roughly E-W) and covered the galaxy ~10" to the W of GRB 990123. The redshift of this galaxy is 0.278 +- 0.001 based on Ca II K and H (393.3 nm and 396.9 nm), G band (400.3 nm) and Mgb (517.4 nm)." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 251 SUBJECT: GRB 990123: Updated Keck Spectroscopy Results DATE: 99/02/05 02:31:18 GMT FROM: George Djorgovski at Caltech/Palomar GRB 990123: Updated Keck Spectroscopy Results S. G. Djorgovski, S. R. Kulkarni (CIT), G. D. Illingworth (UCSC), D. D. Kelson (DTM), J. S. Bloom, S. C. Odewahn, R. R. Gal (CIT), M. Franx (Leiden), P. van Dokkum (Groningen), D. Magee (UCSC), and D. A. Frail (NRAO) note on behalf of the Caltech-UC-CARA-NRAO collaboration: Our re-reduction of the Keck spectrum of the optical transient associated with GRB 990123 (Kelson et al., IAUC 7096) gives the following results: We detect 12 (13) absorption lines in the spectrum of the OT, as follows: W_obs,air W_rest,vac z Line ID 4843.74 1862.78 1.6010 Al III 5267.29 2026.14 1.6004 Zn II 5361.77 2062.23 1.6007 Cr II | blend 5361.77 2062.66 1.6002 Zn II | 5877.17 2260.78 1.6003 Fe II 6096.14 2344.21 1.6012 Fe II 6173.87 2373.73 1.6016 Fe II 6195.29 2382.76 1.6008 Fe II 6725.75 2586.64 1.6009 Fe II 6759.94 2600.18 1.6005 Fe II 7269.47 2796.35 1.6003 Mg II 7289.49 2803.53 1.6008 Mg II 7416.97 2852.97 1.6005 Mg I The mean redshift is 1.6004 +- 0.0005 (random) +- 0.0005 (systematic). This agrees to within the quoted error with the new determination of the absorber redshift by Hjorth et al. (GCN 249). We note the remarkably small velocity dispersion implied by these data, less than about 60 km/s in the restframe, suggesting that the lines arise from a single subgalactic-size cloud (which of course may be a part of the host galaxy's ISM), rather than from an ansamble of clouds moving within the potential well of a normal, massive galaxy. It is also possible that the GRB host is a dwarf galaxy, in which case the object detected near the line of sight both in the K band (Djorgovski et al., GCN 243) and in the R band (Yadigaroglu and Halpern, GCN 248) may be a foreground galaxy. No other convincing absorption systems, and no emission lines are detected in these data, in the useful wavelength range of approximately 4700 to 9000 Angstroms. We do not detect Ca II H+K absorption, nor any other common absorption lines, e.g., Na D, nor any common emission lines (e.g., [O II] 3727, H alpha, H beta, etc.) from either of the two absorption systems originally proposed by Hjorth et al. (GCN 219). We have also measured the redshift of the galaxy approximately 10 arcsec west of the OT. From 4 relatively "clean" lines, Ca II H+K, H beta, and H alpha, we derive for its redshift z = 0.2783 +- 0.0005. From 4 blended lines, CH G-band 4300, Mg I 5173+5184, Fe I + Ca I 5267, and Na D 5893, we derive z = 0.278 +- 0.001, again in an excellent agreement with Hjorth et al. (GCN 249). No absorption or emission lines corresponding to this redshift are seen in the spectrum of the OT. This report may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 252 SUBJECT: GRB 990123: BVRI standards in the field DATE: 99/02/08 06:29:35 GMT FROM: Ram Sagar at UPSO Nilakshi, R.K.S. Yadav, V. Mohan, A.K. Pandey and R.Sagar of U.P. State Observatory, Manora Peak, Nainital, India report: We have determined the Johnson BV and Cousins RI CCD magnitudes of 18 objects in the field of GRB 990123 with the 104-cm Sampurnanand telescope of the U.P. State Observatory, Manora Peak, Nainital under good photometric sky conditions. The photometric standards present in the field of open star cluster M67 have been used for calibration. The BVRI standard magnitudes of these objects alongwith RA, DEC (J2000) and DAOPHOT photometric errors prefixed with S are given below. ------------------------------------------------------------------------ Object RA Dec h m s o ' '' V SV B-V S(B-V) V-R S(V-R) V-I S(V-I) ------------------------------------------------------------------------- 1 15 25 27.0 44 46 23.2 14.84 0.00 0.57 0.00 0.32 0.00 0.58 0.00 2 15 25 36.5 44 44 37.6 15.47 0.00 0.63 0.01 0.36 0.01 0.67 0.01 3 15 25 11.8 44 46 2.1 15.96 0.00 0.64 0.00 0.41 0.01 0.78 0.01 4 15 25 21.1 44 46 46.9 16.28 0.00 0.67 0.00 0.39 0.00 0.71 0.01 5 15 25 38.6 44 43 20.3 16.72 0.00 0.60 0.01 0.32 0.01 0.63 0.01 6 15 25 21.7 44 46 52.7 16.80 0.00 1.35 0.01 0.82 0.00 1.54 0.01 7 15 25 38.8 44 44 30.1 17.65 0.06 1.29 0.07 0.83 0.08 1.34 0.08 8 15 25 17.9 44 46 29.5 18.10 0.01 1.13 0.01 0.66 0.01 1.17 0.01 9 15 25 39.1 44 44 46.1 18.48 0.05 1.32 0.07 0.67 0.08 1.25 0.07 10 15 25 19.6 44 47 53.0 18.66 0.01 1.45 0.02 0.86 0.01 1.64 0.01 11 15 25 19.3 44 45 58.1 18.72 0.01 0.47 0.01 -------- 0.53 0.02 12 15 25 15.6 44 45 5.6 18.96 0.03 0.87 0.04 0.53 0.04 0.98 0.05 13 15 25 32.7 44 44 29.9 19.01 0.01 0.53 0.02 0.37 0.01 0.69 0.02 14 15 25 25.3 44 45 24.7 19.16 0.05 1.36 0.07 0.70 0.07 1.23 0.07 15 15 25 16.4 44 47 28.4 19.65 0.02 1.39 0.04 0.88 0.02 1.71 0.03 16 15 25 13.8 44 44 50.1 19.87 0.03 0.43 0.04 0.27 0.03 0.34 0.06 17 15 25 26.6 44 43 55.3 20.14 0.03 1.06 0.06 0.80 0.03 1.23 0.04 18 15 25 27.5 44 44 43.6 20.31 0.03 0.48 0.05 0.40 0.03 0.43 0.09 -------------------------------------------------------------------- At the Web site http://www.rri.res.in/grb990123/ the manuscript dealing with the above data are available. The title of the paper is " BVRI CCD photometric standards in the field of GRB 990123". It has been accepted for publication in the Bull. Astron. Soc. India. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 253 SUBJECT: GRB990123 observations DATE: 99/02/08 17:31:10 GMT FROM: Christian Veillet at CFHT Christian Veillet reports: The optical transient (OT) associated with the gamma ray burst GRB990123 has been observed with the new wide field camera CFH12k at the prime focus of the 3.6-m CFH Telescope for three consecutive nights on 1999 Feb 5.6, 6.6 and 7.6 by C. Veillet in the course of the French GRB follow-up program at CFHT (M. Boer, CESR, C. Veillet, CFHT). A composite image of the field around the OT has been made from eighteen 10min exposures (six per night). Using the standards published by Nilakshi et al. (GCN 252), the mean R magnitude of the OT averages to R = 23.45 (0.1) on 1999 Feb 6.6. Images of the field, with a detection limit of R=25.0 (3 sigma), can be seen at the Web site http://www.cfht.hawaii.edu/~veillet/grb990123.html. No object is detected in a radius of 5" centered on the OT. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 254 SUBJECT: HST Data for GRB990123 Available DATE: 99/02/09 18:07:15 GMT FROM: Steven Beckwith at STScI HST Images of GRB 990123 Now Publicly Available The Space Telescope Science Institute is pleased to announce that recent observations of GRB 990123 are now available in the HST Data Archive. The program ID is 8394. The three orbits of STIS CCD imaging were done as a Director's Discretionary Program as a service to the astronomical community, in response to suggestions by Fruchter, Kulkarni, and others. The data can also be found in the archive's anonymous ftp area, ftp://archive.stsci.edu/pub/misc/grb/GRB990123/ and gzipped versions of the same fits files are also available in the compressed/ subdirectory. [GCN OP NOTE: I deleted the HTML-version duplicate of the circular that was attached in the original submitted/distributed circular.] //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 255 SUBJECT: GRB 990123: Reduced HST Images DATE: 99/02/09 19:22:51 GMT FROM: Andrew S. Fruchter at STScI Andrew Fruchter, Kailash Sahu, Harry Ferugson, Mario Livio and Mark Metzger on behalf of the larger HST GRB collaboration report: We have reduced the HST STIS CCD clear (50CCD) images of GRB 990123 announced earlier today by the Director of STScI, Steven Beckwith, in GCN 254. We find the optical transient to be superposed on an extended irregular galaxy. A quick photometric reduction shows that the OT has a magnitude of V=25.4 +/- 0.1 and the galaxy has V=24.3 +/- 0.15. The total integrated magnitude of the galaxy and OT is therefore V~24, which agrees with Palomar 5-m observations taken approximately 12 hours before the HST observations, and which will be reported in a succeeding GCN. No correction to the STIS magnitude has yet been made to take into account the colors of the objects, which could change the estimated magnitudes from the broad STIS clear filter by ~0.1 mag. The faint magnitude of the OT suggests that it may be declining more rapidly than the earlier power-law would predict, as suggested by the MDM group in GCN 248. The probable host galaxy is itself composed of several irregular pieces, extended over a region more than 1" across. The major fraction of the light in the host is to the north of the OT, thus agreeing with the probable extension reported by Djorgovski et al. in GCN 243. A gif image as well as the reduced FITS files will be posted by 16:00 EST today (9 February 1999) on http://www.stsci.edu/~fruchter/GRB/990123 We welcome the use of the reduced FITS image by others; however, we ask that those who do use this image cite this GCN, or a formal publication that may succeed it (the bibliographic reference of which would be available on the above web page). //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 256 SUBJECT: GRB 990123: Discovery of the Probable Host Galaxy DATE: 99/02/09 21:41:21 GMT FROM: George Djorgovski at Caltech/Palomar GRB 990123: Discovery of the Probable Host Galaxy S. G. Djorgovski, S. R. Kulkarni, J. S. Bloom, G. Neugebauer, C. Koresko (Caltech), L. Armus (IPAC), S. C. Odewahn, B. R. Oppenheimer, R. R. Gal (Caltech), N. Kobayashi (NAOJ), and D. A. Frail (NRAO), report on behalf of the Caltech-CARA-NRAO GRB collaboration: We confirm the detection of a faint galaxy approximately 0.6 arcsec due north from the optical transient (OT) associated with GRB 990123, in the K-band images obtained with the NIRC instrument at the Keck-I 10-m telescope, on the nights of 29 January 1999 and 6, 7, and 8 February 1999 UT. The presence of this object was already suggested in the Keck K-band images obtained on 27 January 1999 UT by Malkan et al., and its K-band magnitude was estimated to be about 22 to 23 (see Djorgovski et al., GCN 243). The galaxy is clearly resolved from the OT in the images obtained on 29 January by Neugebauer and Armus; it has about an equal magnitude as the OT in the images taken on 7 and 8 February by Kulkarni and Oppenheimer, i.e., K =~ 22 +- 0.7 mag. The K-band light curve containing the light from both objects begins to show a flattening due to the presence of this galaxy. The deviation from the power-law light curve in the K-band (Bloom et al., GCN 240), assumed to have the slope alpha = -1.15 (as measured in the r band), implies the galaxy magnitude K =~ 22.4 (+0.9, -0.4; 1-sigma), in a good agreement with the previous estimates. We interpret this object as the most likely counterpart of the absorber at z = 1.600 (IAUC 7096, GCN 219, GCN 249, GCN 251), and the probable host galaxy of the GRB. Its observed K-band magnitude is reasonable for a normal galaxy at z = 1.6. Analysis of the HST images of the field shows the same object (GCN 255), and further details will be reported shortly. A Keck image of the field will be posted at: http://astro.caltech.edu/~george/grb/grb990123.html This report is citeable. //////////////////////////////////////////////////////////////////////// GRB990123: Rapidly declining afterglows Arnon Dar (Technion-Isael Inst. of Tech.) reports: The sudden fast decline of the radio afterglow of GRB 990123 (GCN Circs. 211, 212, 239, 240) and of the optical afterglow (GCN Circs. 208, 240, 242, 248, 255) may be explained by a sudden deflection or disruption of a glowing jet/plasmoid (e.g., ApJ 500, L93): The glows of decelerating relativistic jets/plasmoids ejected from microquasars, e.g., GRS 1915+105 (Rodriguez and Mirabel astro-ph/980834; SS433 (Hjellming and Johnston 1988, ApJ 328, 600) and from the inner regions of relativistic jets from quasars, blazars and radio galaxies behave like F(nu,t) ~ nu^{-0.75+/-0.25}t^{-1.25+/-0.15}, i.e., like the observed GRB afterglows. This decline steepens suddenly, as a result of jet disruption or deflection, into ~ t^{-2.6+/-0.6} for microquasar jets, and into ~ t^{-4+/-1} in the outer regions of relativistic jets from quasars and radio galaxies (e.g., Bridle & Perley 1984, ARA&A 22, 319). Deflections of relativistic jets/plasmoids from quasars, blazars (e.g. Mrk 421), radio galaxies and microquasars have been observed. If GRB 990123 was jetted then: (1) the present fast decline of the optical afterglow should exhibit a ~t^{-2.6} power-law decline. 2) if the radio afterglow reappears within a week or two due to jet deflection or widening (following sufficient decrease in the bulk motion Lorentz factor), then it is predicted to follow the usual ~nu^{-0.7}t^{-1.2} decline. [GCN OP NOTE (09 Feb 99): This submission is being posted into the archives for GRB990123 without distribution pending the final decission on the issue of content of the Circulars and the possible division.] //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 257 SUBJECT: GRB990123, Optical Observation DATE: 99/02/15 05:21:39 GMT FROM: Jules Halpern at Columbia U. J. P. Halpern, Y. Yadigaroglu, K. M. Leighly, & J. Kemp (Columbia U.) report on behalf of the MDM Observatory GRB follow-up team: "We imaged the field of GRB 990123 in the R band on Feb. 14.50 UT using the MDM Observatory 2.4m telescope. A total of 100 minutes exposure was obtained in seeing of 0.9 arcsec. An object is detected at a position consistent with that of the GRB host galaxy as measured in the HST STIS image (Bloom et al. astro-ph/9902182). Its magnitude is R = 23.77 +/- 0.10 (referenced to the comparison star of GCN #207), equivalent to Gunn r = 24.10. Since this is consistent with the estimate of r = 24.0-24.2 for the host galaxy alone by Bloom et al., we conclude that the optical transient is no longer making a detectable contribution to the total light in ground-based images. We also report a revised magnitude on Feb. 3.54 of R = 23.55 +/- 0.24, after more detailed analysis of those data. Further HST observations are therefore needed to follow the unusual afterglow decay of this most energetic GRB. The latest MDM image will be posted at http://cba.phys.columbia.edu/grb/ This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 260 SUBJECT: GRB990123 observations DATE: 99/02/19 13:42:03 GMT FROM: Christian Veillet at CFHT Christian Veillet reports: The optical transient (OT) associated with the gamma ray burst GRB990123 has been observed with the new wide field camera CFH12k at the prime focus of the 3.6-m CFH Telescope for two additional nights on 1999 Feb. 8.6 and 9.6 by C. Veillet in the course of the French GRB follow-up program at CFHT (M. Boer, CESR, C. Veillet, CFHT) with the assistance of J. Anderson (University of Victoria - Canada), as a continuation of the observations reported in GCN 253 from the three previous nights. Using only the last three nights (image quality better than 1 arc-second), photometric measurements in B, V and R using the star #18 published by Nilakshi et al. (GCN 252) give the following results: R = 23.41 (0.1) on 1999 Feb. 8.6 - 130 mn total integration time V = 24.05 (0.1) on 1999 Feb. 8.6 - 50 mn total integration time B = 24.46 (0.15) on 1999 Feb. 9.6 - 30 mn total integration time The V magnitude is in good agreement with the HST estimate of the OT+galaxy magnitude (V~24 GCN 255). As suspected from the first published image based on the first three nights (GCN 253) with the first two of poor image quality, the surrounding galaxy is now clearly resolved. A composite image in R and contour maps of the GRB area and of a nearby comparison star are available at the Web site http://www.cfht.hawaii.edu/~veillet/grb990123.html This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 261 SUBJECT: GRB990123: Caltech STIS Photometry and Images DATE: 99/02/19 13:52:30 GMT FROM: Steve Odewahn at Caltech S. C. Odewahn, J. S. Bloom, S. Djorgovski, S. R. Kulkarni, and F. Harrison (CIT) report on behalf of the Caltech-NRAO-CARA GRB Collaboration: We have processed the HST STIS images of GRB 990123 using a variety of techniques and have deduced the following magnitudes: Estimates of Gunn r magnitudes from the Median stack STIS image: r(OT) = 25.25 -+0.2 systematic+accidental error r(OT+GAL) = 24.16 -+0.1 accidental error only r(A2) = 27.18 -+0.02 accidental error only r(OT+GAL+A2) = 24.09 Estimates of Gunn r magnitudes from the drizzled STIS image: r(OT) = 25.28 -+0.2 systematic+accidental error r(OT+GAL) = 24.12 -+0.1 systematic+accidental error r(A2) = 27.23 -+0.02 systematic+accidental error r(OT+GAL+A2) = 24.06 Details of the reduction, the image properties and a map defining the apertures for OT, GAL, and A2 (a discrete source 0.9" from the OT) may be found at: http://astro.caltech.edu/~sco/sco1/research/grb/grb990123/stis.html In this website we detail the procedure for obtaining by anonymous ftp our final STIS images, a deep Keck R-band image, and the Palomar 60-inch OT discovery image discussed in GCN 201. These data may be used without any need to cite the source. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 268 SUBJECT: GRB 990123, Field Photometry DATE: 99/02/26 18:13:16 GMT FROM: Arne A. Henden at USNO/USRA BVRI photometry in the field of GRB 990123 was performed with the USNO 1.0-m telescope in Flagstaff during the February dark run. Results of that photometry have been posted at: ftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/grb990123.dat with a more complete description of the photometric procedures in: ftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/grb990123.readme Objects 1-18 in the photometry file are numbered identically to Nilakshi, et. al. (GCN 252). Other objects are either fainter stars in the same field, or else brighter stars within the 11x11 arcmin field of the CCD to be used for field identification. We have omitted the obviously extended objects 7, 9, and 16. We note some photometric differences between Nilakshi and this new photometry. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 307 SUBJECT: GRB 990123, optical monitoring DATE: 99/05/10 19:04:54 GMT FROM: Arne A. Henden at USNO/USRA The U. S. Naval Observatory GRB Team (A. Henden (USRA/USNO), R. Stone, F. Vrba, C. Luginbuhl, B. Canzian, J. Munn, S. Levine, H. Guetter (USNO)) report: We have been monitoring the Optical Transient position for GRB 990123 with the USNOFS 0.2-m FASTT system (Stone et. al. 1996, AJ 111, 1721). As this is a converted transit telescope, we were not able to begin observations until the field started to transit in darkness. However, we have single-epoch data for the following nights (yymmdd UT): 990225 990302 990303 990304 990305 990309 990310 990316 990320 990321 990322 990323 990329 990330 990331 Typical limiting magnitude at R was 18.3. We saw no recurrence of the transient during this period. We also report single-epoch JHK measures (with the USNO 1.55-m telescope and infrared camera) on 990202, and J measures on 990328 and 990427. Typical limiting magnitude at J was 17.5. No recurrence was seen. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 346 SUBJECT: Late Afterglows of GRBs 990510, 990123 DATE: 99/05/27 23:17:04 GMT FROM: Arnon Dar at Technion-Israel Inst. of Tech Gravitational collapse of neutron stars (NS) to (di)quark stars (QS) due to phase transition or mass accretion are expected to generate highly relativistic jets plus a mildly relativistic spherical explosion (e.g., Dar 1999a,b). The jets, when pointing in our direction, produce GRBs, and afterglows that decline with time like F(t)\sim t^{-\alpha}/[1+(t/t_0)^{\beta-\alpha}] The spherical explosion is expected to add to it an afterglow like that of GRB 980425/SN 1998bw (Galama et al 1998; , time-dilated and redshifted by 1+z. Assuming ``a standard explosion'' = 1998bw at redshift 1+z: F(t)\sim t^{-\alpha}/[1+(t/t_0)^{\beta-\alpha}]+ SN1998bw[1+z] For GRB 990510, \alpha= 0.76, \beta=2.4, and t_0=1.57 days is the time when the jet begins to spread. The spherical explosion is expected to produce an up turn in the time-decline of the afterglow of GRB 990510 in the R band before the end of May, reach a maximum with R magnitude m=26.7\pm 0.3 between early and mid June, decline fastly by two additional magnitudes by mid August and then decline exponentially with a much smaller rate, with a half time (1+z)=2.62 longer than that of GRB 980425/SN 1998bw, i.e., t(half)=140 days. An identical behavior is expected from the late afterglow (t>20 days after explosion) of GRB 990123 (z=1.61, Kulkarni et al. 1999). [The above behavior explains better the behavior of the afterglow of GRB 970228 (z=0.69; Kulkarni 1999), t_max=20 days, m(max)=25 in the R band) than a single power-law and consistent with all the other measured GRB afterglows]. HST is urged to conduct observations of GRBs 990510 and 990123 in order to test these predictions and verify/falsify the proposed NS-->QS origin of GRBs. Dar, A. 1999a, A\&A, in press (astro-ph/9902017) Dar, A. 199b astro-ph/9905315 Galama, T. J. et al. 1998, Nature 395, 670 Kulkarni, S. R. et al 1999a, Nature, 398, 389 McKenzie, E. H. \& Schaefer, B. E. 1999 astro-ph/9904397 Stanek, K. Z. 1999, astro-ph/9905304 Vreeswijk, P. M. et al. 1999 GCN Circ. No. 324 //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 354 SUBJECT: Late-time HST/STIS Observation of GRB 990123 DATE: 99/06/22 08:49:41 GMT FROM: Andrew S. Fruchter at STScI TITLE: Late-time HST Observations of GRB 990123 Subject: HST/STIS Observations of GRB 990123 A. Fruchter (STScI), S. Thorsett (Princeton), and E. Pian (ITESRE) report for the HST GRB collaboration: The field of GRB 990123 was reobserved by HST with the STIS CCD in open filter (50CCD) mode during two orbits on 23 March 1999, or 59.5 days after the GRB. The total exposure time was 5040s. The optical transient was visible, but had declined by 2.1 +/- 0.2 mags from that observed on 8 February 1999 by HST (Fruchter et al. 1999, Kulkarni et al 1999), to V = 27.55 +/- 0.2 mags. Both of the HST observations of the OT of GRB 990123 fall well below the t^{-1.09} power-law behavior of the OT during the first three days (Fruchter et al. 1999). The 8 February observation lies more than 2 mags below the continuation of such a power-law. Additionally, a power-law fit of the flux density of the OT finds between the two HST observations finds t^{-1.52 +/- 0.15}; this slope is nearly 3 sigma steeper than that found through day 3, but is also noticeably shallower than that predicted from a break in the power-law due to either our now observing the edge of a collimated outflow (Meszaros and Rees 1999) or the sideways expansion of such an outflow (Kulkarni et al. 1999, Rhoads 1999). The HST images from both epochs will be made available in gif format at http://www.stsci.edu/~fruchter/GRB/990123. The reduced HST data from the first epoch are also available in fits format at this site. The reduced data of the second observation will be made available later, in accordance with the HST GRB Collaboration policy of making reduced data publicly available upon publication in a refereed journal. References: Fruchter, A. et al., 1999, Ap. J. (Letters), 519, L13. Kulkarni, S. et al., 1999, Nature, 398, 389. Meszaros, P. and Rees, M., 1999, MNRAS (submitted), astro-ph/9902367. Rhoads, J., 1999, Ap. J. (submitted), astro-ph/990399. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 712 SUBJECT: GRB 990123: Late-time HST/STIS 50CCD observations of the host DATE: 00/06/17 02:51:46 GMT FROM: Andrew S. Fruchter at STScI A. Fruchter (STScI), S. Thorsett (UCSB), R. Wijers (SUNY) report for the larger HST GRB collaboration: Public HST observations in the red (LP) STIS filter should shortly be available of the host galaxy of GRB 990123. We therefore report here on the results of late-time imaging of the host by our group using the wide-band open (50CCD) filter. The images described here can be found at http://www.stsci.edu/~fruchter/GRB , and will be submitted to a journal shortly. The field of GRB 990123 was reobserved by HST with the STIS CCD in open filter (50CCD) mode during two orbits on 7 February 2000, or 380 days after the GRB. The optical transient was no longer visible. However we have been able to use this image to further refine our earlier photometry on the OT (Fruchter et al. 1999a,b). We now find a V magnitude for the OT of 25.4 +/- 0.1 on 8 February 1999 and V = 27.7 +/- 0.15 on 23 March 1999, implying that the late time late-time light curve falls as t^{-1.7 +/- 0.1}. This represents a break of about 0.65 from the power-law decay a couple of days after outburst, and thus is roughly consistent with the beaming model of Meszaros and Rees (1999). However, this also agrees within the errors with the power-law of the early time light curve reported by ROTSE, and this may suggest a connection between the early and late-time emission. The GRB is found to reside near the edge of the visible stellar field of the host, and is not superposed on a strong region of star-formation. References: Akerlof, C. et al, 1999, Nature, 398 400. Fruchter, A. et al., 1999, Ap. J. (Letters), 519, L13. Fruchter, A. et al., 1999, GCN 354. Meszaros, P. and Rees, M., 1998, MNRAS, 306L, 39. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 715 SUBJECT: GRB990123, HST/STIS observations of the host galaxy DATE: 00/06/18 17:15:20 GMT FROM: Stephen Holland at IFA, U of Aarhus Stephen Holland, Johan Fynbo, Bjarne Thomsen (University of Aarhus), Michael Andersen (University of Oulu), Gunnlaugur Bjornsson (University of Iceland), Jens Hjorth (University of Copenhagen), Andreas Jaunsen (University of Oslo), Priya Natarajan (Universities of Cambridge, & Yale), and Nial Tanvir (University of Hertfordshire) We have obtained 8224 seconds of STIS images with the F28X50LP (long pass) aperture of the host galaxy of GRB 990123. This data was taken as part of the Survey of the Host Galaxies of Gamma-Ray Bursts (Holland et al. GCN 698) approximately 509 days after the burst. Combined images are now available at "http://www.ifa.au.dk/~hst/grb_hosts/data/index.html". Using the light curve fits of Holland et al. (2000, submitted to A&A) we predict that the optical afterglow will have R = 31.6 on 15 June 2000, and thus will not be visible in the STIS images. Therefore, we used aperture photometry to determine the AB magnitudes, in the long pass filter, of the three knots found by Holland & Hjorth (1999, A&A, 344, L67). We find the following colours for the three extended knots where CL is the AB magnitude in the STIS clear aperture, LP is the AB magnitude in the STIS long pass aperture, and beta is the corresponding spectral index, f = k*nu^beta. Knot CL LP CL-LP beta 1 28.3 28.2 +0.1 +/- 0.4 -0.4 2 28.1 27.5 +0.6 +/- 0.4 -2.6 3 28.0 27.5 +0.5 +/- 0.4 -2.2 The GRB occurred on the southeast edge of Knot 1. This knot is approximately one sigma bluer than the other two knots, and two sigma bluer than the overall colour of the galaxy (V-R = 0.43 +/- 0.18; Castro-Tirado et al., 1999, Science 283, 2069). This suggests that Knot 1 might be undergoing stronger star formation than the rest of the galaxy. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 732 SUBJECT: GRB990123: Late-time HST/STIS observations of the host DATE: 00/06/27 22:30:58 GMT FROM: Andrew S. Fruchter at STScI A. Fruchter (STScI) reports for the HST GRB collaboration: It has come to our attention that the web page reported in our last circular, GCN 712, did not load properly for outside users. The GRB 990123 page that they saw was unchanged from last year. We have corrected this problem. Readers wishing to see the light curve of the OT, or the late-time imageing of the host, can either click on the animated gif of the decline of GRB 990123 at http://www.stsci.edu/~fruchter/GRB or go directly to http://www.stsci.edu/~fruchter/GRB/990123 . We have now also included a color image of the host and the wider field about GRB 990123 created using the both the open (50CCD) images (see GCN 712) and the more recent long pass STIS data (GCN 715).