THIS FILE CHANGES WITH TIME -- HIT THE RELOAD BUTTON NOW! ///////////////////////////////////////////////////////////////////// GRB 980425 21:49:10.56 UT SOD=78550.56 sec TJD=10928 DOY=115 This is the same burst as BATSE Trigger 6707. However, there is no real-time GCN/BATSE information because this burst occurred during the electrical power outage in GSFC/PACOR/GCN facilities. This archive also contains reports on the apparent supernove discovered in the SAX-NFI field around the original gamma-ray burst. ///////////////////////////////////////////////////////////////////// Circular No. 6884 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 Phone 617-495-7244/7440/7444 (for emergency use only) GRB 980425 P. Soffitta, M. Feroci, and L. Piro, Istituto Astrofisica Spaziale, CNR, Rome; J. in 't Zand and J. Heise, Space Research Organization of the Netherlands (SRON), Utrecht; L. Di Ciolo, BeppoSAX Science Operation Center, Rome; J. M. Muller, BeppoSAX Science Data Center, Rome, and SRON; and E. Palazzi and F. Frontera, Istituto Tecnologie e Studio Radiazioni Extraterrestri, CNR, Bologna, write: "The BeppoSAX Gamma-Ray Burst Monitor was triggered by a gamma-ray burst on Apr. 25.90915 UT. The gamma-ray burst appears to be single-peaked and not structured. A preliminary analysis reveals a duration of about 30 s and a peak intensity of 350 counts/s in the energy band 40-700 keV. The burst was also detected in Wide Field Camera no. 2 with comparable duration and a peak intensity of about 3 Crab (2-28 keV). The position derived by the WFC image is R.A. = 19h34m54s, Decl. = -52o49'.9 (equinox 2000.0), with an error radius of 8' that includes uncertainties due to a non-optimum attitude control configuration. A follow-up observation with BeppoSAX narrow-field instruments is in progress." (C) Copyright 1998 CBAT 1998 April 26 (6884) Daniel W. E. Green ///////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 60 SUBJECT: GRB 980425 optical observations DATE: 98/04/29 18:17:16 GMT FROM: Titus Galama at U.Amsterdam T.J. Galama, P.M. Vreeswijk, P.J. Groot, B. Stappers (University of Amsterdam); E. Pian, F. Frontera, E. Palazzi, N. Masetti (CNR, Bologna); L. Nicastro (IFACI-CNR, Palermo); M. Feroci (CNR, Roma); R.G. Strom (NFRA and U of Amsterdam); C. Kouveliotou (USRA/MSFC); J. van Paradijs (U of Amsterdam and U of Alabama in Huntsville) report: "Comparison of Digitized Sky Survey (DSS) and ESO NTT images obtained on April 28.37 UT (1998) shows a point source in the BeppoSAX WFC error box of GRB 980425 (IAUC 6884) which is not visible in the DSS. The object is also detected in red and blue band images taken at the 50in telecope at the Australian National University's Mt. Stromlo Observatory on April 26.63 UT (1800s), April 26.81 UT (1800s) and Apr 28.68 UT (1800s). It is located at RA 19:35:03.17, DEC -52:50:46.1 (J2000), offset from the nucleus of the barred spiral galaxy ESO 184-82 (in the DN 1931-529 group of galaxies; Duus & Newall, ApJS 35, 209, 1977) and coincident with the spiral arms. The object varies by less than 0.2 magnitudes between April 26.63 and 28.83 and has a blue magnitude of 16.2 +/- 0.5. It is therefore not clear whether the source is related to GRB 980425, or whether it is, e.g., a supernova. Images of the object and the SB galaxy can be found at http://www.astro.uva.nl/titus. Comparison of the Mt. Stromlo April 26.63 UT and Apr 28.68 UT red band images at the location of the X-ray source (BeppoSAX GRB MAIL N. 98/11) shows no variation > 0.2 mag down to about 21 mag." This work is based partly upon images obtained by the MACHO Project with the 50in telecope at the Australian National University's Mt. Stromlo Observatory. This message is citeable. ///////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 61 SUBJECT: report on BSAX observations of GRB980425 DATE: 98/04/29 20:23:22 GMT FROM: Elena Pian at ITESRE-CNR,Bologna GRB980425 E. Pian, Istituto TESRE, CNR, Bologna, Italy, L. A. Antonelli, M. R. Daniele, S. Rebecchi, SAX-SDC, Rome, Italy, V. Torroni, SAX-SOC, Rome, Italy, G. Gennaro, SAX-OCC, Rome, Italy, M. Feroci, L. Piro, IAS, CNR, Rome, Italy, report: "The BeppoSAX Wide Field Camera error box of GRB980425 (IAUC 6884) was observed with the BeppoSAX Narrow Field Instruments (NFI) starting about 10.0 hr after the burst in the period April 26.31-28.16 UT. Preliminary analysis of the data shows two previously unknown X-ray sources in the LECS and MECS: 1SAXJ1935.0-5248 and 1SAXJ1935.3-5252, located at RA = 19h35m04s, Dec = -52o48'33'' and at RA = 19h35m21s, Dec = -52o52'19'' (equinox 2000.0), respectively, with an error radius of 1' each. These positions are 2' and 4'.7 away from the centroid of the WFC error box, respectively. During the first 27.7 hours of observation, the average count rates in the two MECS units (1.6-10 keV) were (4.5 +- 0.7)x10E-3 cts/s, corresponding to (3.0 +- 0.4)x10E-13 erg sE-1 cmE-2 in the 2-10 keV range, for 1SAXJ1935.0-5248 and (2.4 +- 0.5)x10E-3 cts/s for 1SAXJ1935.3-5252, equivalent to (1.6 +- 0.3)x10E-13 erg sE-1 cmE-2 (2-10 keV). The measurements during the subsequent 16.6 hours showed that 1SAXJ1935.0-5248 did not vary significantly from the first epoch. 1SAXJ1935.3-5252 was not detected at the second epoch, with a 3 sigma upper limit of 1.8x10E-3 cts/s. This indicates a decay by a factor of 1.3 or more in 22 hours. A further BeppoSAX observation is already planned to monitor the behavior of both sources." ///////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 62 SUBJECT: GRB 980425 optical observations DATE: 98/04/30 11:20:39 GMT FROM: Titus Galama at U.Amsterdam T.J. Galama, P.M. Vreeswijk, P.J. Groot (University of Amsterdam); E. Pian, F. Frontera, E. Palazzi, N. Masetti (CNR, Bologna); L. Nicastro (IFACI-CNR, Palermo); M. Feroci (CNR, Roma); R.G. Strom (NFRA and U of Amsterdam); C. Kouveliotou (USRA/MSFC); J. van Paradijs (U of Amsterdam and U of Alabama in Huntsville) report: "Comparison of red band images of the error box of GRB 980425 (Soffitta et al. 1998; IAUC 6884) taken at the 50in telescope at the Australian National University's Mt. Stromlo Observatory on April 26.63 UT (1800s) and April 28.68 UT (1800s) shows no variation > 0.2 mag down to about 21 mag at the location of the transient BeppoSAX NFI X-ray source 1SAXJ1935.3-5252 (Pian et al. 1998; GCN #61)." This work is based partly upon images obtained by the MACHO Project with the 50in telecope at the Australian National University's Mt. Stromlo Observatory. This message is citeable. ///////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 63 SUBJECT: GRB980425: Radio Observations DATE: 98/05/01 20:44:46 GMT FROM: Dale A Frail at NRAO GRB 980425: Radio Observations M. Wieringa (ATNF), D.A. Frail (NRAO), S.R. Kulkarni (Caltech), J.L. Higdon (ATNF), R. Wark (ATNF), and the BeppoSAX GRB Team report: Radio observations were made with the Australian Telescope Compact Array beginning on April 28.73 and April 28.98 UT at 6cm and 3cm, centered on the position of 1SAXJ1935.0-5248, an X-ray source detected by the NFI on BeppoSAX (Pian et al. 1998; GCN #61). In addition, radio observations of the transient BeppoSAX NFI source 1SAXJ1935.3-5252 were made (also at 6cm and 3cm) on April 29.79 and April 30.00 UT No radio sources were detected in the 1' error radius of the two NFI sources. Typical three-sigma limits were 0.26 mJy and 0.3 mJy at 3cm and 6cm, respectively. Three radio sources are detected in the 8' error radius of the BeppoSAX WFC. There is one object just outside the error circle of 1SAXJ1935.0-5248 at RA 19:34:56.49, Dec -52:49:04.9 (J2000) with a flux density of 2.4 mJy at 6cm and 1.1 mJy at 3cm. The brightest radio source in the field is at RA 19:35:03.31, Dec -52:50:44.7 (posn. error +/-0.1"). It coincides within the likely optical astrometric errors to the candidate supernova proposed by Galama et al. (1998, GCN# 60) in the barred spiral Galaxy ESO 184-82. Approximate flux densities (corrected for primary beam attenuation) on April 28 were 9.3 mJy and 17 mJy at 6cm and 3cm, respectively. Further observations of 1SAXJ1935.3-5252 are planned. This message is citable. ///////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 64 SUBJECT: GRB980425: optical obs. DATE: 98/05/01 20:56:14 GMT FROM: Dale A Frail at NRAO Optical Observations of GRB 980425 J.S. Bloom, S.R. Kulkarni, S.G. Djorgovski (Caltech), P. McCarthy (OCIW) and D.Frail (NRAO) report on behalf of the Caltech-OCIW GRB effort: "Kaspar von Braun (U. Mich) imaged the field of the X-ray source reported in IAUC 6884 (Soffitta et al.) on the 40-inch at Las Campanas Observatory in Chile. Two sets of images were obtained in the R band at April 27.4 UT and April 28.4 UT. We scrutinized the images in the vicinity of the two BeppoSAX NFI sources reported by L. Piro and Pian et al. (GCN #61). In the 1-arcmin error circle of the fading X-ray source SAXJ1935.3-5252 we found no source with variability greater than 0.2 mag for R < 21 mag. We thank Kaspar von Braun and Mario Mateo for their help on these observations. " This report may be cited. ///////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 65 SUBJECT: GRB 980425 optical observations DATE: 98/05/02 20:57:29 GMT FROM: Titus Galama at U.Amsterdam P.M. Vreeswijk, T.J. Galama, P.J. Groot (University of Amsterdam); F. Frontera, E. Palazzi, N. Masetti (CNR, Bologna); L. Nicastro (IFACI-CNR, Palermo); E. Costa, L. Piro (CNR, Roma); R.G. Strom (NFRA and U of Amsterdam); C. Kouveliotou (USRA/MSFC); J. van Paradijs (U of Amsterdam and U of Alabama in Huntsville); J.F. Gonzalez, V. Doublier (ESO, Chile) report: "Comparison of R band images of the error box of GRB 980425 (Soffitta et al. 1998; IAUC 6884) taken at the ESO NTT telescope on April 28.37 UT (900s) and May 1.33 UT (900s) shows no variation > 0.3 mag down to 22.8 mag at the location of the transient BeppoSAX NFI X-ray source 1SAXJ1935.3-5252 (Pian et al. 1998; GCN #61)." This message is citeable. ///////////////////////////////////////////////////////////////////// Circular No. 6895 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 Phone 617-495-7244/7440/7444 (for emergency use only) GRB 980425 T. J. Galama and P. M. Vreeswijk, University of Amsterdam; E. Pian and F. Frontera, CNR, Bologna; and V. Doublier and J.-F. Gonzalez, European Southern Observatory (ESO), report: "Comparison of ESO New Technology Telescope images obtained on Apr. 28.4 and May 1.3 UT shows that a point source in the BeppoSAX WFC error box of GRB 980425 (IAUC 6884) not visible in the Digitized Sky Survey brightened by 0.7 mag from R = 15.7 to 15.0 (+/- 0.1). The object is located at R.A. = 19h35m03s.31, Decl. = -52o50'44".8 (equinox 2000.0), offset from the nucleus of the face-on spiral galaxy (ESO 184-G82). Its position does not coincide with either of the two x-ray sources in the error box of GRB 980425 (Pian et al. 1998, GCN 61), and it is therefore not clear whether the source is related to GRB 980425, or whether it is, e.g., a supernova. A finding chart for it can be found at http://www.astro.uva.nl/titus/grb980425.html." C. Lidman, V. Doublier, J.-F. Gonzalez, T. Augusteijn, O. R. Hainaut, H. Boehnhardt, F. Patat, and B. Leibundgut, ESO, write: "We have observed the supernova candidate discovered by Galama et al. (see above). The object is located in a spiral arm of the barred spiral galaxy ESO 184-G82, the redshift of which was measured at 2528 km/s (heliocentric) from a spectrum obtained with the 3.6-m NTT (+ EMMI). The object displays a steep magnitude increase, as indicated by the following photometry (+/- 0.05 mag) with the NTT (Danish 1.54-m telescope on May 3): Apr. 28.4 UT, R = 15.77; May 1.3, R = 14.83; 3.30-3.38, V = 14.81, R = 14.35, I = 14.40; 4.4, V = 14.23, R = 14.28, I = 14.27; 6.4, V = 14.00, R = 14.04, I = 14.30. With the ESO/MPI 2.2-m telescope (+ IRAC2) on May 6.4, we obtained the following preliminary photometry J = 11.5, H = 11.6; K = 11.9. A finding chart and secondary photometric standards are available at http://sc6.sc.eso.org/~ohainaut/SN. Spectra were obtained on May 1.4 (NTT), 3.4 (1.5-m Danish telescope + DFOSC), 4.4 (ESO 3.6-m telescope + EFOSC2), and 6.4 (NTT). Apart from H-alpha (probably from the galaxy), the mostly featureless spectra display some broad lines in the range 350-500 nm, then a steep decrease over 500-700 nm, and a plateau from 700 to 1000 nm, with very broad bumps at 620 and 800 nm (spectra of the region 350-900 nm are displayed at the same URL). The relative intensity of the different regions of the spectrum is changing from day to day. The absence of H lines suggests that the object is not a type-II supernova; the lack of Si at 615 nm indicates that it is not a regular type-Ia supernova. The nature of this puzzling object still evades identification, as does its relation to GRB 980425 or to the galaxy. The ESO team continues monitoring." (C) Copyright 1998 CBAT 1998 May 7 (6895) Daniel W. E. Green ///////////////////////////////////////////////////////////////////// Circular No. 6896 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 Phone 617-495-7244/7440/7444 (for emergency use only) GRB 980425 C. Tinney, R. Stathakis, and R. Cannon, Anglo-Australian Observatory; and T. Galama, University of Amsterdam, report spectroscopy of the possible supernova in the galaxy ESO 184-G82 associated with the gamma-ray burst GRB 980425 (IAUC 6895), obtained with the 3.9-m Anglo-Australian Telescope (+ 2dF spectrograph; range 620-720 nm, resolution 0.15 nm) on May 2.74118 UT. There is weak (EW = -0.18 nm) H-alpha emission, and possible S II emission indicating a galaxy redshift of z = 0.0085 +/- 0.0002. M. Wieringa, Australia Telescope National Facility (ATNF); D. A. Frail, National Radio Astronomy Observatory; S. R. Kulkarni, California Institute of Technology (CIT); J. L. Higdon and R. Wark, ATNF; J. S. Bloom, CIT; and the BeppoSAX GRB Team report: "Radio observations at 6 and 3 cm were made toward two x-ray sources in the field-of-view of GRB 980425 (IAUC 6884; GCN 61) with the Australian Telescope Compact Array starting on Apr. 28.73, 29.79, and May 5.55 UT. No radio sources were detected within the 1' error radius of the two NFI sources. There is a bright radio source at R.A. = 19h35m03s.31, Decl. = -52o50'44".7 (equinox 2000.0; +/- 0".1). On Apr. 28 the flux densities of the source were 9 and 13 mJy at 6 and 3 cm, respectively, and were similar on Apr. 29 (9.9 and 13 mJy). On May 5 the flux densities of the source had increased dramatically, to 39 and 48 mJy at 6 and 3 cm, respectively. The position of the variable radio source coincides with the optical astrometric position given by Galama et al. on IAUC 6895. At the distance to ESO 184-G82, as implied by its redshift (Tinney et al., above), the radio source is already three times more luminous than SN 1988Z, one of the most luminous radio supernovae discovered, and is still brightening. Given the small likelihood of finding such an unusual radio source in the field, we suggest that the radio source may be related to GRB 980425." (C) Copyright 1998 CBAT 1998 May 7 (6896) Daniel W. E. Green ///////////////////////////////////////////////////////////////////// Circular No. 6898 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 Phone 617-495-7244/7440/7444 (for emergency use only) GRB 980425 P. M. Vreeswijk, University of Amsterdam, writes that he provided the wrong position for the optical position of the suspected supernova in ESO 184-G82 on IAUC 6895, lines 7-8; the correct position should read R.A. = 19h35m03s.17, Decl. = -52o50'46".1 (equinox 2000.0). (C) Copyright 1998 CBAT 1998 May 8 (6898) Daniel W. E. Green ///////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 67 SUBJECT: GRB980425 BATSE observations DATE: 98/05/08 21:46:07 GMT FROM: R Marc Kippen at BATSE/UAH/MSFC GRB 980425: BATSE Observations R. M. Kippen (University of Alabama in Huntsville) reports on behalf of the BATSE GRB team: GRB 980425 (IAUC 6884) was detected by BATSE on Apr. 25.90913 UT as trigger number 6707. The event consisted of a single pulse lasting about 40 s with little resolvable structure. Its peak flux (50-300 keV; integrated over 1 s) and fluence (> 20 keV) are 0.96 (-/+ 0.05) photons cmE-2 sE-1 and 4.0 (-/+ 0.6) x 10E-6 erg cmE-2, respectively, ranking it near the middle of the BATSE burst flux/fluence distribution. The BATSE location is consistent with that of the BeppoSAX-WFC and the reported SAX-NFI x-ray counterpart (GCN 61). Please note that this report has been delayed due to an interruption of BATSE data delivery from GSFC. Bursts are normally fully processed within a few days. The BATSE lightcurve and location map can be found at http://www.batse.msfc.nasa.gov/~kippen/batserbr/ This message is citeable. ///////////////////////////////////////////////////////////////////// Circular No. 6899 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 Phone 617-495-7244/7440/7444 (for emergency use only) GRB 980425 J. S. Bloom, California Institute of Technology (CIT); D. Frail, National Radio Astronomy Observatory; and S. R. Kulkarni, CIT, report on behalf of the CIT gamma-ray burst team: "Using the 2.54-m reflector at Las Campanas, S. Vogel and M. Regan obtained V, R, and I images of the field of GRB 980425 (IAUC 6884) near the presumed supernova discovered by Galama et al. (IAUC 6895, 6898). Using the secondary standards of Lidman et al. (IAUC 6895), we determine that the transient has continued to brighten, with the following derived magnitudes (+/- 0.05): May 8.311 UT, V = 13.87; 8.306, R = 13.84; 8.309, I = 13.98. The error comes predominately from the zero-point uncertainty. The contribution to the flux from a nearby star about 4".9 to the northwest and the host galaxy is negligible (< 0.02 mag). A composite light curve from published fluxes can be obtained at http://astro.caltech.edu/~jsb/ltcurve_980425.ps. It is still unclear as to the connection between the presumed supernova and GRB 980425. In order to correlate the time of both, an accurate light curve must be obtained." (C) Copyright 1998 CBAT 1998 May 10 (6899) Daniel W. E. Green ///////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 69 SUBJECT: BSAX Observations of GRB980425 field DATE: 98/05/12 13:58:01 GMT FROM: Elena Pian at ITESRE-CNR,Bologna GRB980425 E. Pian, F. Frontera, Istituto TESRE, CNR, Bologna, Italy, L.A. Antonelli, SAX-SDC, Rome, Italy, L. Piro, IAS, CNR, Rome, Italy, also on behalf of the BeppoSAX team report: "A second Target-of-Opportunity observation of the BeppoSAX Wide Field Camera (WFC) error box of GRB980425 (IAUC 6884) was done with the BeppoSAX Narrow Field Instruments (NFI) in May 2.604-3.646 UT. Preliminary analysis of the MECS data shows that the source 1SAXJ1935.0-5248 reported in GCN N. 61 has a count rate of (3.0 +- 0.5)x10E-3 cts/s in the 1.6-10 keV range (1.9x10E-13 erg sE-1 cmE-2 in 2-10 keV), and therefore has decreased only with marginal significance with respect to the TOO observation performed in April 26.31-28.16 UT. A 3-sigma upper limit of 1.5x10E-3 cts/s in the 1.6-10 keV range is found for 1SAXJ1935.3-5252. If one assumes for the X-ray emission of this source a power-law temporal decay f ~ (t - t0)^{-alpha}, the measured upper limit is consistent with the alpha >0.4 fading observed between the first and second part of the first TOO NFI pointing (GCN N. 61), as well as with the alpha ~1.4 decrease between the 2-10 keV flux preliminarily estimated from the WFC detection (~2.6x10E-08 erg sE-1 cmE-2, Pian et al. 1998, in preparation) and that observed in the first 27.7 hours of the first NFI pointing (GCN N. 61). This variability behavior is typical of X-ray afterglows of GRBs so far detected. ///////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 70 SUBJECT: GRB 980425 Brightness Temperature DATE: 98/05/13 00:52:08 GMT FROM: Shri Kulkarni at Caltech S. R. Kulkarni, J. S. Bloom, California Institute of Technology, D. A. Frail, National Radio Astronomy Observatory, R. Ekers, M. Wieringa, R. Wark, J. L. Higdon, Australian Telescope National Facility report: Within the localization of GRB 980425 (IAUC 6884) Galama et al. (IAUC 6895) reported a possible supernova candidate for which Wieringa et al. (IAUC 6896) saw a brightening radio source. The object appears to be an unusual supernova based on its spectrum (IAUC 6895). The continued brightening in the optical (IAUC 6899) suggests that the supernova is young and is compatible with an explosion on or around April 24, 1998, the epoch of GRB 980425. For an assumed expansion speed of 20,000 km/s and a distance of 44 Mpc to the host galaxy of the supernova (from the redshift given in IAUC 6896) we derive a brightness temperature of 3x10^14 K from the observed 39 mJy at 6 cm on May 5 (IAUC 6896). This is in excess of the usual Compton limit of 10^12 K. Despite this, no X-ray emission is seen (GCN #69). Thus we are forced to invoke relativistic expansion speed which results in a larger source size and correspondingly smaller brightness temperature. We suggest that the radio emission arises in a relativistic shock and the optical emission in a standard low velocity shock. The model predicts that the radio source should not exhibit diffractive scintillation. We urge observers to carry out higher frequency radio observations and IR observations as these directly measure the particle spectrum that gives rise to the radio emission. The urgency is that the radio emission may cease once the relativistic shock runs into denser ambient gas. Parenthetically, we note that it is possible that such a fast moving shock could generate an initial burst of gamma-rays." ///////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 71 SUBJECT: GRB 980425 Radio Light Curve DATE: 98/05/13 03:15:41 GMT FROM: Dale A Frail at NRAO M. H. Wieringa, R. M. Wark, J. L. Higdon, Australia Telescope National Facility, D. A. Frail, National Radio Astronomy Observatory, S. R. Kulkarni, J. S. Bloom, California Institute of Technology report: Monitoring of the time-variable radio source (GCN 63, IAUC 6896, GCN 70) coincident with a supernova candidate proposed by Galama et al. (GCN 60, IAUC 6895) has continued with the Australia Telescope Compact Array at 20, 13, 6 and 3 cm. The radio source may have reached a peak on May 7 1998 at 6 and 3 cm of 45 and 49 mJy, respectively. A radio light curve, spectra, and individual maps are available at http://www.narrabri.atnf.csiro.au/public/grb/grb980425.html ///////////////////////////////////////////////////////////////////// Circular No. 6901 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 Phone 617-495-7244/7440/7444 (for emergency use only) SUPERNOVA 1998bw IN ESO 184-G82 E. M. Sadler, University of Sydney; R. A. Stathakis and B. J. Boyle, Anglo-Australian Observatory; and R. D. Ekers, Australia Telescope National Facility, report: "The spectrum of the variable object in ESO 184-G82 (IAUC 6895, 6896, 6899) closely resembles the pre-maximum spectrum of the type-Ib supernova 1983N (Richtler and Sadler 1983, A.Ap. 128, L3). The detection of prompt radio emission (IAUC 6896; see http://www.narrabri.atnf.csiro.au/public/grb for more recent data) is also typical of type-Ib supernovae (though this object is about 30 times more luminous at radio wavelengths than was SN 1983N). It therefore seems certain that the object in ESO 184-G82 is a supernova discovered before maximum light. The optical lightcurve (IAUC 6895, 6899) implies that the supernova explosion probably occurred sometime during Apr. 21-27 -- i.e., consistent with the supernova and the gamma-ray burst GRB 980425 occurring simultaneously. We suggest that the two events are associated, and that we may be seeing a supernova in which the core has collapsed to a black hole (plus accretion disk) rather than a neutron star, after models proposed by Woosley (1993, Ap.J. 405, 273) and Paczynski (1998, Ap.J. 484, L45)." (C) Copyright 1998 CBAT 1998 May 13 (6901) Daniel W. E. Green ///////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 155 SUBJECT: GRB980425: X-ray revised positions DATE: 98/10/20 21:26:03 GMT FROM: SAX Science Operations at IAS/CNR Frascati GRB980425: revised SAX-NFI positions L. Piro, IAS/CNR, Rome, Italy, R.C. Butler, ASI, Rome, Italy, F. Fiore, A. Antonelli, BeppoSAX SDC, Roma, E. Pian, ITesre, Bologna, Italy, report: The majority of BeppoSAX observations were performed with the star tracker Z (i.e., the one co-aligned with the NFI) in the attitude control loop. However, a few observations could not be performed in this configuration, but had to be carried out with the X and Y star trackers only. We have found out that, in these very infrequent cases, the attitude reconstruction could have an error of up to 3'. This problem does not affect observations accomplished after May 5, 1998. Prior to this date, the only GRB which was observed by the NFI in this configuration is GB980425. The revised coordinates (equinox 2000.0) of the two sources found in the WFC error box (Pian et al., GCN 61) are: 1SAXJ1935.0-5248, RA = 19h35m05.9s, Dec =-52o50'03"; 1SAXJ1935.3-5252, RA = 19h35m22.9s, Dec =-52o53'49", with a conservative error radius of 1.5'. Both updated positions are still within the WFC error box (Soffitta et al., IAU Circ. No. 6884). However, 1SAXJ1935.0-5248 is at 50" from SN1998bw (Galama et al. 1998, Nature, in press, astro-ph/9806175; Kulkarni et al., Nature, in press, astro-ph/9807001) and therefore consistent with it, while the variable source 1SAXJ1935.3-5252 is 3' away, i.e., inconsistent. ///////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 156 SUBJECT: GRB980425 Optical Follow-up DATE: 98/10/22 05:47:13 GMT FROM: Jules Halpern at Columbia U. J. P. Halpern, Columbia University, reports: I obtained optical spectra of objects in the error circle of the variable X-ray source 1SAXJ1935.3-5252 (Pian et al. GCN 61,69) using the CTIO 1.5m telescope on Oct. 17-21. A total of 24 objects in the original error circle (Pian et al. GCN 61) and the revised error circle (Piro et al. GCN 155) were observed, completing this spectroscopic survey to a limiting magnitude of 18. No compelling candidate for identification was found at this level. Thus, 1SAXJ1935.3-5252 remains a plausible candidate for the afterglow of GRB980425. The brightest galaxy in this field, of approximate magnitude 17.5, has narrow emission lines of H-alpha and [N II] 658 nm at z = 0.142, but no evidence of nuclear activity. Its position is RA = 19h35m27.6s, Dec = -52o53'00" (J2000), which is within both the old and the new error circles. Deeper spectroscopy in this field using larger telescopes would be worthwhile, since the optical counterpart of 1SAXJ1935.3-5252 could easily be fainter than the limit surveyed here. If a definitive identification cannot be obtained, more X-ray observations of 1SAXJ1935.3-5252 are needed to determine if this X-ray source recurs. ///////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 158 SUBJECT: BeppoSAX NFI Observation of GRB980425 DATE: 98/12/16 14:23:16 GMT FROM: Elena Pian at ITESRE-CNR,Bologna GRB980425 E. Pian, ITESRE, CNR, Bologna, Italy, L. A. Antonelli, Osservatorio di Monteporzio, Rome, Italy, L. Piro, and M. Feroci, IAS, CNR, Rome, Italy report: "The field of GRB980425 (IAUC 6884) was re-observed with the BeppoSAX Narrow Field Instruments on 1998 November 10.754-12.004 UT. Preliminary analysis of the MECS data shows that the source 1SAXJ1935.0-5248 reported in the GCN N. 61 and 69, the position of which (see updated coordinates in GCN N. 155) is consistent with that of the supernova SN1998bw (Galama et al. 1998, Nature 395, 670), has a count rate of (1.8 +- 0.4)x10E-03 cts/s in the 1.6-10 keV range, and therefore has decreased by approximately a factor of two with respect to the average level observed in April-May (see GCN N. 61 and 69). This suggests the presence of variable X-ray emission from the supernova. This preliminary analysis shows also that the source 1SAXJ1935.0-5248 is slightly extended. The source 1SAXJ1935.3-5252 (see GCN N. 61, 69, 155) is not detected down to a 3-sigma limit of 1.4E-03 cts/s. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 286 SUBJECT: GRB980425 Optical observations of exponential decline at late time DATE: 99/03/30 21:40:33 GMT FROM: Brad Schaefer at Yale U Bradley E. Schaefer and Eric H. McKenzie (Yale University) report: "We have obtained 139 photometric observations in B, V, and I of the late time light curve for SN1998bw associated with GRB980425. These demonstrate a strikingly linear decline in magnitude versus time. Our data was taken with the Yale 1.0-m telescope on Cerro Tololo between 27 June and 28 October 1998. We used standard IRAF reduction and the comparison stars of Galama et al. (http://www.astro.uva.nl/~titus/grb980425/grb980425chart.html). During the time interval of our observations, the light from the underlying galaxy (ESO 184-G82) was insignificant in our photometry. Our first and last data nights had measured photometry as follows: JD2450992.9 B=16.68+-0.03, V=15.79+-0.02, I=15.16+-0.03 JD2451115.6 B=18.35+-0.06, V=18.09+-0.05, I=17.33+-0.06 Between these two nights, all our photometry is perfectly consistent with an exactly linear decline in magnitudes (hence an exponential decline in luminosity). Our measured uniform decline rates are as follows: B 0.0141+-0.0002 mag/day for equivalent half-life of 53.4+-0.8 days V 0.0184+-0.0003 mag/day for equivalent half-life of 40.9+-0.7 days I 0.0181+-0.0003 mag/day for equivalent half-life of 41.6+-0.7 days The observed exponential decline is in contradiction to the theoretical predictions of Iwamoto et al. (1998, Nature, 395, 672) and Iwamoto (1999, ApJ, astro-ph/9810400), which claims that the decline will be as a power law. The observed exponential decline has a rate similar to that expected from the decay of radioactive cobalt as modified by the effects due to the expansion of the shell. So it is reasonable to conclude that the late-time light curve of SN1998bw is being powered by radioactive cobalt. This then implies that the underlying explosion mechanism must create large masses of radioactive cobalt. The light curve of SN1998bw is significantly different from all previously known supernovae. For a comparison with Type Ia events, the decline rate of SN1998bw is the same in B but not V and I as for Type Ia events, while SN1998bw does not show the bump in the I band light curve from 20-50 days after peak. A comparison with Type Ic events is difficult since their lights curves are not well defined, yet the late time decline rate of Type Ic events is substantially smaller than for SN1998bw. Our observations of SN1998bw are continuing with the Yale 1.0-m telescope. However, since the source has come out from behind the Sun, the light from the galaxy provides an increasingly significant obstacle to accurate photometry. Perhaps future accurate photometry must await the complete fading of SN1998bw to allow for subtraction of the galaxy light." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 704 SUBJECT: GRB980425, HST/STIS observations of the host galaxy DATE: 00/06/15 13:12:23 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 (University of Cambridge, & Yale), and Nial Tanvir (University of Hertfordshire) We have obtained 1240 seconds of STIS images with the 50CCD (clear) aperture and 1185 seconds with the F28X50LP (long pass) aperture of the host galaxy of GRB 980425. This data was taken as part of the Survey of the Host Galaxies of Gamma-Ray Bursts (Holland et al. GCN 698) approximately 778 days after the burst. Combined images are now available at "http://www.ifa.au.dk/~hst/grb_hosts/data/index.html" and a GIF image of the host galaxy is available at "http://www.ifa.au.dk/~hst/grb_hosts/data/grb980425_colour.gif". An astrometric solution from VLT V-, R-, and I-band images (P.I., B. Libundgut) suggests that the supernova is located at X = 987 +/- 2, Y = 1064 +/- 2 on our drizzled long pass image. This is in an extended object with AB magnitudes of 26.2 +/- 0.1 in the STIS clear filter and 26.3 +/- 0.1 in the STIS long pass filter. An extrapolation of the V-band late-time light curve of SN 1998bw (McKenzie & Schaefer 1999, PASP, 111, 964) suggests that the SN remnant will have a magnitude of ~28.4 in the clear filter, which is near the detection limit of our data. The extended object has a full-width at half-maximum, in the long pass image, of 0.13 arcseconds. When the resolution limit (0.088 arcsec) is taken into account the object has a diameter of, at most, ~0.09 arcsec. For z = 0.0085, and a cosmology with H0 = 65, Omega_matter = 0.2 and Omega_lambda = 0, this corresponds to a diameter of less than ~17 pc. The colour and size of the object is consistent with it being a young star cluster. The extended object is embedded in a large extended feature (possibly an HI region) with a diameter of ~75 pc and an estimated colour of V-R ~= 0.7 +/- 0.3. A GIF image of the region containing the supernova is available at "http://www.ifa.au.dk/~hst/grb_hosts/data/grb980425cd_sfr.gif". A detailed analysis of these images is in progress (Holland et al. 2000, in preparation).