//////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 290 SUBJECT: IPN localization for GRB990506 DATE: 99/05/06 20:28:10 GMT FROM: Kevin Hurley at UCBerkeley/SSL K. Hurley, on behalf of the Ulysses GRB team, and Scott Barthelmy, on behalf of the GCN team, report: We have obtained a preliminary IPN annulus for GRB990506 (BATSE #7549) using coarse time resolution BATSE/GCN and Ulysses data. This annulus is refined with respect to that in the GCN/IPN Notice sent out at 19:14:36 UT. The annulus is centered at RA(2000)= 144.960 degrees, Decl(2000)=-7.324 degrees, and has a radius of 37.424 +/- 0.035 degrees (3 sigma). It intersects both the BATSE Locburst location for this burst as well as the RXTE PCA source location sent out today at 17:27:37 UT. The latter intersection defines an ~4' wide by 1 degree long error box whose corners are: RA(2000) DEC(2000) 11 h 54 m 23.69 s -26 o 57 ' 59 " 11 h 56 m 15.28 s -26 o 03 ' 34 " 11 h 54 m 06.48 s -26 o 56 ' 11 " 11 h 55 m 58.07 s -26 o 01 ' 50 " Thus if the RXTE PCA source is found to be fading, it is quite likely to be the X-ray afterglow of the GRB. An image may be found at http://ssl.berkeley/edu/ipn3/990506. The IPN annulus can be refined considerably. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 291 SUBJECT: New IPN/RXTE error box for GRB990506 DATE: 99/05/06 20:47:37 GMT FROM: Kevin Hurley at UCBerkeley/SSL K. Hurley, on behalf of the Ulysses GRB team, and S. Barthelmy, on behalf of the GCN team, report: The IPN annulus reported in GCN #290 intersects the most recent RXTE/PCA source position sent out at 20:29:37, to form an ~50 square arcminute error box whose corners are: RA(2000) Dec(2000) 11 h 54 m 37.79 s -26 o 51 ' 20 " 11 h 55 m 0.33 s -26 o 40 ' 35 " 11 h 54 m 22.47 s -26 o 48 ' 39 " 11 h 54 m 41.30 s -26 o 39 ' 41 " A new image has been posted at http://ssl.berkeley.edu/ipn3/990506. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 292 SUBJECT: GRB990506 observation plan DATE: 99/05/06 21:29:49 GMT FROM: Blaise Canzian at USNO The U.S. Naval Observatory GRB team (F. J. Vrba, C. B. Luginbuhl, A. A. Henden, S. E. Levine, J. Munn, B. Canzian, H. H. Guetter), D. H. Hartmann (Clemson Univ.), and M. C. Jennings (IGPP, UCR visitor) reports that it intends to observe the IPN/RXTE error box for GRB990506 reported in GCN 291 with the USNO 1.0-meter telescope in Rc-band, beginning at about 0330 07May99 UT. Since we expect photometric conditions for the night, we plan to produce a photometric calibration sequence in B, V, Rc, and Ic bands for the field. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 293 SUBJECT: GRB990506 Optical observations DATE: 99/05/07 02:41:57 GMT FROM: Brad Schaefer at Yale U Bradley E. Schaefer (Yale) reports: "I have obtained two 15-minute R band observations of the joint RXTE/IPN region for GRB990506 (with the 5.1' RXTE position) starting at 23:20 UT 6 May 1999 (less than 12 hours after the burst) with the Yale 1.0 m telescope on Cerro Tololo. In a comparison with the the Digital Sky Survey, no new sources were seen to the DSS limit, nor is any obvious change visible between the images. We are continuing observations. Detailed analysis and deeper images/comparisons might yet yield a counterpart." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 294 SUBJECT: GRB 990506, optical observations DATE: 99/05/07 06:18:50 GMT FROM: Fredrick J. Vrba at USNO The U.S. Naval Observatory GRB team (F.J. Vrba, A.A. Henden, B. Canzian, C.B. Luginbuhl, S.E. Levine, H.H. Guetter, J.A. Munn), D.H. Hartmann (Clemson Univ.), M.C. Jennings (IGPP, UCR visitor), and A.J. Castro-Tirado (LAEFF-INTA, IAA-CSIC, Spain), M.R. Zapatero-Osorio, R. Casas, V. Motta (IAC, Spain), J. Gorosabel (LAEFF-INTA), and J. Greiner (AIP, Germany) report observations of the GRB 990506 field, obtained at the U.S. Naval Observatory, Flagstaff Station with the 1.0-m reflector. Observations in B, V, R(Cousins), and I(Cousins) using a CCD with an 11x11 arcmin field were centered approximately at the center of the intersection of the IPN3 (GCN 291) and the revised RXTE x-ray localization (of UT 1999 May 07 02:31:42) and thus cover an area several times the size of this intersection. A series of local standards covering this field and based on all-sky photometry was established and preliminary photometric values, with +/- 0.05 mag uncertainty to V = 18.5, are available at ftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/grb990506.dat, along with astrometry accurate to approximately 0.1 arcsec. The RXTE/IPN3 locus was inspected for objects which had visually different brightness than on the Digital Sky Survey (DSS). One object, located near the center of this intersection at R.A. = 11:54:52.92, DEC = -26:43:39.9 (+/- 0.2 arcsec in both coordinates)(J2000), was notably absent from the DSS image. However, at V = 21.0, V-R = 1.6 (+/- 0.2) its apparently red color (if not due to variability) might be why it is not visible on the DSS. As of the time of this writing, observations are continuuing in order to determine if this object is variable. This GCN note can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 295 SUBJECT: GRB 990506, optical observations from +1 to +3 hours DATE: 99/05/07 07:54:16 GMT FROM: Jin Zhu at Beijing Obs J. Zhu, H. T. Zhang, on behalf of the BAO GRB follow-up team, report: "Observations of the GRB 990506 field were made with the BAO 0.6/0.9m Schmidt telescope in Xinglong from 1 hour and 10 minutes after the GRB, using R-band filter and 2k x 2k CCD. The 16 observation fields (each of 58' x 58') covered 3.6 degrees x 3.6 degrees field centered at the BACODINE/HUNTSVILLE/LOCBURST position, so it contains the IPN/RXTE box announced later in (GCN 291) by Hurley and Barthelmy. Observations for that area were made by two 300s exposures at 12:41:47 UT and 14:41:38 UT respectively (about 1 and 3 hours after the GRB), and comparison with DSS-I image shows no additional source (appeared in both of the two images we made) in a detection limit of about R=19.0. No source could be seen at the position of F.J. Vrba et. al (GCN 294). Data reduction was delayed by electral power failure in observation site, and wider part around that area will be checked later. This report may be cited." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 296 SUBJECT: GRB 990506, armchair astronomy DATE: 99/05/07 08:07:16 GMT FROM: Jules Halpern at Columbia U. J. P. Halpern reports (from his office) that an optical object referred to in GCN #294 as "notably absent from the DSS image" is in fact visible on the STScI digitized version of a 1992 April 24 UK Schmidt plate, at J2000 position RA 11:54:52.9, Dec -26:43:40 with an uncertainty of about 1" (astrometry based on 12 stars from the USNO A-2.0 list with rms of 0.2"). While a variety of possible scenarios leap to mind to anyone familiar with the recent history of this subject, caution is urged. Go see for yourselves. This GCN note need not be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 297 SUBJECT: GRB 990506: Limits on the possible optical transient DATE: 99/05/07 18:58:14 GMT FROM: George Djorgovski at Caltech/Palomar GRB 990506: Limits on the possible optical transient W. L. W. Sargent, T. A. Small, D. T. Frayer, S. R. Kulkarni, S. G. Djorgovski, J. S. Bloom (Caltech) report on behalf of the Caltech-CARA-NRAO Collaboration: A spectrum of the possible optical counterpart of GRB 990506 proposed by Vrba et al. (GCN 294) was obtained at the Keck-II 10-m telescope by Sargent and Small on 7 May 1999 UT. This object is a Galactic M-type star, and is thus presumably unrelated to the burst (cf. also Halpern, GCN 296). Images of the XTE/IPN error box were obtained at the Palomar 60-inch telescope by Frayer on 7 May 1999 UT, reaching considerably deeper than the DSS. No new optical objects brighter than the DSS limit were found. Furhter imaging observations are planned. This note can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 298 SUBJECT: Refined IPN error box for GRB990506 DATE: 99/05/07 20:49:45 GMT FROM: Kevin Hurley at UCBerkeley/SSL K. Hurley, on behalf of the Ulysses GRB team, C. Kouveliotou and R. M. Kippen, on behalf of the BATSE GRB team, and T. Cline, on behalf of the NEAR GRB team, report: We have obtained a refined position for this burst using higher time resolution data, and adding the data of the NEAR spacecraft. This results in a true error box, as opposed to just a triangulation annulus. This error box is consistent with that obtained from the intersection of the Ulysses-BATSE annulus with the RXTE error circle, and therefore confirms that the fading X-ray source is indeed related to the GRB, but in this preliminary analysis, it does not reduce its size. Thus the refined error box (area ~30 sq. arcmin.) is defined by the new Ulysses-BATSE annulus and the RXTE error circle. The corners are at: RA(2000) Dec(2000) 11 h 54 m 33 s -26 o 50 ' 59 " 11 h 54 m 56 s -26 o 40 ' 07 " 11 h 54 m 24 s -26 o 49 ' 16 " 11 h 54 m 45 s -26 o 39 ' 36 " Reductions in the widths of the annuli of the order of a factor of two or more will be possible. An image may be viewed at http://ssl.berkeley.edu/ipn3/990506. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 299 SUBJECT: GRB990506 observation plan DATE: 99/05/07 23:17:44 GMT FROM: Fredrick J. Vrba at USNO The U.S. Naval Observatory GRB team (F. J. Vrba, C. B. Luginbuhl, A. A. Henden, S. E. Levine, J. Munn, B. Canzian, H. H. Guetter), D. H. Hartmann (Clemson Univ.), and M. C. Jennings (IGPP, UCR visitor) reports that it intends to repeat observations of IPN/RXTE error box for GRB990506 for comparison with data taken 7 May 1999 UT (for pointing and observational details see GCN 294). The data taken 7 May reach an R magnitude of approximately 23-24, and we expect to reach similar limits tonight. If any variable sources are detected, we expect to release the position and approximate photometric measures via GCN by 0700-0800 UT 8 May 1999, which may be sufficient notice for observers located further west. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 300 SUBJECT: GRB 990506, optical observations DATE: 99/05/08 09:36:46 GMT FROM: Arne A. Henden at USNO/USRA The U.S. Naval Observatory GRB team (F.J. Vrba, A.A. Henden, C. B. Luginbuhl, B. Canzian, S.E. Levine, H.H. Guetter, J.A. Munn), D.H. Hartmann (Clemson Univ.), M.C. Jennings (IGPP, UCR visitor), and A.J. Castro-Tirado (LAEFF-INTA, IAA-CSIC, Spain), M.R. Zapatero-Osorio, R. Casas, V. Motta (IAC, Spain), J. Gorosabel (LAEFF-INTA), and J. Greiner (AIP, Germany) report a second night of calibrated photometric observations of the GRB 990506 field, obtained at the U.S. Naval Observatory, Flagstaff Station with the 1.0-m reflector. Observations in B, V, R(Cousins), and I(Cousins) using a CCD with an 11x11 arcmin field were centered approximately at the center of the intersection of the IPN3 (GCN 291) and the revised RXTE x-ray localization (of UT 1999 May 07 02:31:42). Deep Rc-band images formed from 12 stacked 10-minute exposures were obtained on both nights. No clearly variable object within the IPN annulus was seen, down to a detection limit of roughly Rc=23. One object 1.6 arcmin outside the revised IPN annulus (GCN 298) but within the revised RXTE localization (GCN/RXTE_PCA Burst Position Notice of 990507 02:31:42 UT) appears to be variable, fading from approximately Rc=22.0 (+/- 0.2mag) on 990507 UT to below our detection limit on 990508 UT. The coordinates of this object are 11:54:57.80, -26:43:03.8 (J2000, +/- 0.2 arcsec). A 2.7 arcmin square finding chart (NE = upper left) for this object can be found on ftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/grb990506.gif The BVRcIc photometric calibration file in this directory (grb990506.dat) will be revised in the near future to reflect the second night of all-sky photometry. This GCN note can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 301 SUBJECT: GRB 990506 optical observations DATE: 99/05/08 17:33:10 GMT FROM: Paul Vreeswijk at U of Amsterdam P.M. Vreeswijk and E. Rol (University of Amsterdam) report on behalf of the Amsterdam/Huntsville GRB optical follow-up team: We measured the object at RA 11:54:57.80, Decl -26:43:03.8 (J2000) reported by Vrba et al. to be variable (GCN #300) in our Harris-R band images, taken with the WIYN telescope at May 8.18 UT. We find R = 22.21 +/- 0.15 using an aperture size which is twice the seeing disk of 1.05"). Our measurement was taken at about the same time as where Vrba et al. report Rc > about 23. The data were calibrated using the RUBIN 149 field of the Landolt catalog (Landolt et al. 1992, 104, 340). The value we find for the reference star at RA 11:54:51.6, Decl -26:43:4.09 (J2000), R = 16.1 +/- 0.1 is in good agreement with the Vrba et al. calibration for this star: R = 16.11. Based on our result we believe the object is constant, but we urge more observations to confirm/reject the variable nature of this object. This message is citeable. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 302 SUBJECT: GRB 990506 optical observations DATE: 99/05/08 21:14:49 GMT FROM: Krzysztof Z. Stanek at CfA P. M. Garnavich, K. Z. Stanek and M. R. Garcia (Harvard-Smithsonian CfA) report on behalf of the CfA GRB optical follow-up team: We measured the object at RA 11:54:57.77, Decl -26:43:02.9 (J2000) (coordinates based on the GSC catalog), reported by Vrba et al. to be variable (GCN #300), in our R-band images taken with the 1.2-meter telescope at the F. L. Whipple Obs. by N. Caldwell (May 7) and K. J. Rines (May 8). We find R=22.6 +/- 0.3 on average of two 15-min images (May 7 03:15 UT) and R=22.5 =/- 0.3 on average of two 15-min images (May 8 UT 04:48). The data were calibrated using Landolt standard star RU149. This is consistent with the Vrba et al. object being non-variable. This message is citeable. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 303 SUBJECT: GRB 990506, Optical Observations DATE: 99/05/09 03:10:15 GMT FROM: Jules Halpern at Columbia U. R. Uglesich and B. Sugerman (Columbia U.) report: We obtained R-band images of the refined RXTE/IPN error region of GRB 990506 (Hurley et al. GCN #298) using the MDM Observatory 1.3m and a CCD covering a 10.7 x 10.7 arcmin field. On the nights of May 7 UT and May 8 UT, seeing was approximately 1.3 and 1.5 arcseconds, respectively. Exposure times were 75 minutes on the first night and 100 minutes on the second. The Landolt standard star field of PG 1047+003 was used for calibration. The object at (J2000) 11:54:57.8, -26:43:03.8, which was reported as possibly variable by Vrba et al. (GCN #300), is measured at R = 22.43 +/- 0.15 on May 7.2, and R = 22.38 +/- 0.18 on May 8.2, thus confirming the conclusions of Vreeswijk & Rol (GCN 301) and Garnavich et al. (GCN #302) that it is not variable. [GCN OP NOTE (10May99): At the author's request (JH), the last sentence (of a humorous perspective) of the originally submitted circular was removed from this archived copy, as it does not follow the content guidelines of the Circulars.] //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 305 SUBJECT: GRB 990506, optical observations DATE: 99/05/10 17:55:55 GMT FROM: Arne A. Henden at USNO/USRA The U.S. Naval Observatory GRB team (F.J. Vrba, A.A. Henden, B. Canzian, C.B. Luginbuhl, S.E. Levine, H.H. Guetter, J.A. Munn), D.H. Hartmann (Clemson Univ.), M.C. Jennings (IGPP, UCR visitor) report an updated BVRcIc photometry file for the field of GRB 990506. This file can be found at: ftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/grb990506.dat Two photometric nights with a wide variety of Landolt standards having large color and airmass differences were used. We were more concerned with deep R-band imaging, and so only calibrated the field with shorter BVRcIc exposures. Typical errors are 0.05mag at V=18, with stars reported down to approximately V=20. Star pairs that are separated by less than 5 arcsec are reported as single objects or at least have their photometry contaminated by their neighbors and should therefore be ignored. This GCN note can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 306 SUBJECT: GRB 990506: BATSE Observations DATE: 99/05/10 18:01:10 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 990506 was detected by BATSE on 1999 May 6.474664 as trigger number 7549. The event was strong and consisted of a multi-peaked temporal structure lasting >150 s, with significant spectral evolution. The T50 and T90 durations are 112.06 (-/+ 0.09) s and 131.33 (-/+ 0.20) s, respectively. The burst's peak flux (50-300 keV; integrated over 1.024 s) and fluence (>20 keV) are 18.58 (-/+ 0.13) photons cmE-2 sE-1 and 2.23 (-/+ 0.02) x 10E-4 erg cmE-2, respectively---ranking it in the top 2% (1%) 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 = 0.909 (-/+ 0.003), which is average among BATSE bursts of this duration. The BATSE burst location is consistent with that measured by the IPN (BATSE/Ulysses/NEAR; GCN 298) and was used to initiate an RXTE-PCA scan observation that resulted in the detection of a fading x-ray source; probably the GRB afterglow (see GCN alert notices). 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- [GCN OP NOTE (10May99): Due to a programming problem in processing this Circular so close in time to the previous Circular, the NUMBER was erroneously assigned to be 305, when in fact it should have been 306. The archive copies have been fixed.] //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 308 SUBJECT: GRB 990506 Radio Observations DATE: 99/05/10 19:15:21 GMT FROM: Greg Taylor at NRAO G. B. Taylor (NRAO), D. A. Frail (NRAO), S. R. Kulkarni (Caltech), and J. S. Bloom (Caltech) on behalf of the Caltech-NRAO collaboration report: "On 1999 May 08.2 UT and 1999 May 09.2 UT we carried out VLA observations at 8.4 GHz of the refined RXTE/IPN localization (Hurley et al., GCN 298) for GRB 990506. Although there are four radio sources stronger than 100 microJy in the field, none were shown to be variable. The rms noise level of the images is approximately 30 microJy/beam. Further VLA observations are planned to monitor this field. This message is citeable." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 327 SUBJECT: GRB 990506 R band observations DATE: 99/05/14 14:57:41 GMT FROM: Nicola Masetti at ITeSRE,CNR,Bologna N. Masetti, E. Palazzi, E. Pian, F. Frontera (ITESRE, CNR, Bologna), P.M. Vreeswijk, E. Rol, T.J. Galama (U. of Amsterdam), M. Della Valle (U. of Padua), E. Costa, M. Feroci, L. Piro (IAS, CNR, Rome), J. van Paradijs (U. of Amsterdam and U. of Alabama in Huntsville), C. Kouveliotou (NASA-MSFC/USRA), O. Hainaut, A. Pizzella (ESO-La Silla), and D. Koester (Institut fuer Astronomie und Astrophysik, Kiel), on behalf of the BeppoSAX and Amsterdam/Huntsville GRB optical follow-up teams, report: "Images of the GRB 990506 refined error box (Hurley et al., GCN #298) were acquired with start times 1999 May 7.09, 7.26, 8.04, 9.98 and 10.00 UT (exposure times are reported below) at ESO-La Silla with the 2.2m telescope plus WFI. Zero-point R calibration was determined using the photometry by Vrba et al. (GCN #305) with an accuracy of 0.07 mag. Comparison between the 15-min images of May 7.09 and 8.04 shows no object varying by more than 0.3 magnitudes (3-sigma) down to R~22.6 within the GRB error box. In order to reach a deeper magnitude limit, we summed the images of May 7 (total limiting magnitude: R~24.0) and compared them with that of May 9 and with that of May 10. In this case no object varying by more than 0.3 magnitudes down to R~23.0 is present inside the error box. In all cases, no clearly variable object was seen within the IPN error box down to the detection limits of the frames. Limiting magnitudes for the five epochs cited above are reported in the following table: Start time (UT) Exp. time R mag ---------------------------------------- 1999 May 07.09 15 min. 23.8 1999 May 07.26 15 min. 23.0 1999 May 08.04 15 min. 23.6 1999 May 09.98 30 min. 24.3 1999 May 10.00 30 min. 24.3 This message can be cited." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 342 SUBJECT: GRB 990506 optical observation DATE: 99/05/22 13:24:59 GMT FROM: Holger Pedersen at Copenhagen U Obs H. Pedersen, B. L. Jensen, J. Hjorth (Copenhagen), M. Holman (CfA, USA), K. Aksnes, T. Grav, N. Haug, A. O. Jaunsen (Oslo), M. I. Andersen, and H. Korhonen (NOT), report: We have observed the position of GRB 990506, using the ALFOSC instrument on the 2.56-m Nordic Optical Telescope, La Palma, Spain. We covered almost the entire IPN+RXTE error box (Hurley et al., GCN 298), using two separate pointings, each of which is 6' x 6'. At each position, we obtained a 480 s R-band exposure, between 1999 May 6.91 - 7.05 UT (seeing 0.9" - 1.2" FWHM) and a 240 s R-band exposure, on 1999 May 7.91 UT (seeing 0.7" FWHM). We have compared the exposures internally, finding no evidence for variable objects to a limiting magnitude of R = 22.0, for variability amplitude above 0.3 magnitude. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 350 SUBJECT: GRB 990506 Radio Transient DATE: 99/06/15 18:28:45 GMT FROM: Greg Taylor at NRAO G. B. Taylor (NRAO), D. A. Frail (NRAO) and S. R. Kulkarni (Caltech) report: "We have continued to monitor the four radio sources detected (GCN 308) within the RXTE/IPN localization (GCN 298) for GRB 990506. Some time between May 8 and May 22 one of these sources dropped from 0.54 mJy at 8.4 GHz to below our detection limit (30-40 microJy), while the rest remained constant. In order to confirm or reject the possibility that this object is an Active Galactic Nucleus we initiated a multi-frequency monitoring program. We have recently analyzed the data taken between May 22 and June 12 and found that the source remains undetectable. Our data lead us to conclude that an AGN identification is unlikely, and that the transient source, hereafter VLA J115450.1-2640.6, is the radio afterglow from GRB 990506. VLA J115450.1-2640.6 was located at (J2000) R.A.= 11:54:50.14 (+/-0.04), Dec.=-26:40:35.2 (+/-0.8). We urge all optical/IR observers to re-investigate their images at this precise location for any sign of a variable object." This message is citeable. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 351 SUBJECT: Optical Observations of GRB 990506 DATE: 99/06/15 18:34:56 GMT FROM: Josh Bloom at CIT Optical Observations of GRB 990506 J. S. Bloom, S. G. Djorgovski, S. R. Kulkarni, and B. A. Jacoby (Caltech), on behalf of the Caltech-NRAO-CARA GRB collaboration, report: "On June 11.25 UT, we obtained a total of 1500-s R-band integration of the field of GRB 990506 (Hurley et al.; GCN #290) with the Low-Resolution Imaging Spectrometer (LRIS) on the Keck II 10-m telescope on Mauna Kea, Hawaii. An astrometric plate solution was obtained relative to the USNO A2.0 catalog with a statistical error of 0.23, 0.26 arcsec (ra, dec). Coincident with the position of the fading radio source (Taylor et al.; GCN #350) is a faint extended (NE-SW) galaxy with an irregular (and possibly interacting) morphology. Assuming the star at ra: 11:54:54.7, dec: -26:41:15.2 (J2000) has R=18.5 (Henden et al; GCN #305), we find a preliminary magnitude of the presumed host galaxy of GRB 990506 to be R=24.8 +/- 0.2. This message can be cited." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 352 SUBJECT: GRB 990506 - Optical Observations DATE: 99/06/16 16:03:20 GMT FROM: Holger Pedersen at Copenhagen U Obs H. Pedersen, J. Hjorth, B. L. Jensen (Copenhagen), A. O. Jaunsen (Oslo), and S. Holland (Aarhus) report on behalf of a larger collaboration: "We have re-inspected our optical (R-band) images of GRB 990506 (GCN #342) obtained on 6.96 May 1999 and 7.91 May 1999 UT. We find no convincing evidence for any stellar or extended object at the position of the proposed radio transient (GCN #350), neither in the sum image, nor in subsets. For the first night, we estimate a limiting magnitude of R > 23.5 (for point sources). Our images are available upon request." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 353 SUBJECT: GRB 990506 - clarification to GCN 352 DATE: 99/06/17 09:28:08 GMT FROM: Holger Pedersen at Copenhagen U Obs It has come to my attention that the phrasing of GCN 352 is misleading. I would like to clarify that the discussed NOT data from 6.96 May and 7.91 May 1999 are consistent with the detection of a presumed host galaxy, done at Keck II (GCN 351). Holger Pedersen //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 731 SUBJECT: GRB 990506, HST/STIS Observations of the Host Galaxy DATE: 00/06/27 13:02:28 GMT FROM: Jens Hjorth at U.Copenhagen Stephen Holland, Bjarne Thomsen (University of Aarhus), Michael Andersen (University of Oulu), Gunnlaugur Bjornsson (University of Iceland), Johan Fynbo, Jens Hjorth (University of Copenhagen), Andreas Jaunsen (University of Oslo), Priya Natarajan (University of Cambridge, & Yale), and Nial Tanvir (University of Hertfordshire) We have obtained 7856 seconds of STIS images with the 50CCD (clear) aperture and 8000 seconds with the F28X50LP (long pass) aperture of the sky where the radio afterglow associated with GRB 990506 was detected. This data was taken as part of the Survey of the Host Galaxies of Gamma-Ray Bursts (Holland et al. GCN 698) approximately 413 days after the burst. Combined (drizzled) FITS and GIF images are now available at the interim web site "http://www.astro.uio.no/~ajaunsen/grb-hosts/". The images will be made available at the official survey web site "http://www.ifa.au.dk/~hst/grb_hosts/data/index.html" next week. At the location of the radio afterglow (Taylor et al. astro-ph/0005379) there is a very compact galaxy (FWHM ~ 0.14") which we identify as the probable host galaxy for GRB 990506. This galaxy does not appear to be associated or interacting with a larger galaxy (2" in extent) located 2 arcsec to the north east (the "northeast knot" of Taylor et al.). A preliminary photometric calibration of the STIS data yields R = 25.0 +- 0.3 for the host galaxy. It thus appears to be marginally fainter than the value R = 24.4 +- 0.3 measured on 11 June 1999 (36 days after the burst) in LRIS/Keck II images. This could indicate a contribution from an optical transient (afterglow or supernova) at the time of the Keck observations. A more accurate transformation from 50CCD and F28X50LP to Cousins R is however necessary to rule out calibration errors. We finally note that the radio source R2, identified by Taylor et al. to be a QSO at z = 0.273, is resolved in the STIS images. The morphology is that of a spiral galaxy (2 arcsec in diameter) with a bright nucleus and several knots in the spiral arms. Thus, R2 is a radio loud QSO with a spiral host galaxy.