Gamma-ray Burst 990506

A Gamma-Ray Burst was detected by BATSE (trigger 7549) on 1999 May 6, 11:23:30 UT. RXTE-PCA started scanning a 8(R.A.) x 6(Dec.) deg. region at 14:26 UT. A previously unknown X-ray source was detected, and localized to 0.1 deg accuracy. Triangulation with Ulysses further constrained the position (see below).

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none yet

• GCN/RXTE alert
  

  TITLE:           GCN/RXTE_PCA BURST POSITION NOTICE
  NOTICE_DATE:     Thu 06 May 99 17:27:37 UT
  NOTICE_TYPE:     RXTE-PCA
  TRIGGER_NUM:     7549
  GRB_DATE:        11304 TJD;   126 DOY;   99/05/06
  GRB_TIME:        41010.94 SOD {11:23:30.94} UT
  GRB_RXTE_RA:     178.80d {+11h 55m 12s} (J2000),
                   178.79d {+11h 55m 10s} (current),
                   178.16d {+11h 52m 39s} (1950)
  GRB_RXTE_DEC:    -26.50d {-26d 29' 59"} (J2000),
                   -26.50d {-26d 29' 46"} (current),
                   -26.22d {-26d 13' 17"} (1950)
  GRB_RXTE_ERROR:  0.500 [deg radius, statistical only]
  GRB_RXTE_INTEN:  1.50 [mCrab]
  SUN_POSTN:        43.04d {+02h 52m 09s}  +16.48d {+16d 28' 59"}
  SUN_DIST:        137.85 [deg]
  MOON_POSTN:      290.74d {+19h 22m 57s}  -19.72d {-19d 43' 03"}
  MOON_DIST:        99.46 [deg]
  PROG_LEVEL:      3
  COMMENTS:        RXTE-PCA GRB Coordinates.  
  COMMENTS:        The RXTE-PCA observation started at 99/05/06 14:25:28 UT.  
  COMMENTS:        RXTE/PCA detected 1.5 mCrab source during   
  COMMENTS:        the scans at around RA=178.8 and Dec=-26.5.  
  COMMENTS:        The position uncertainty is 0.5 degree at  
  COMMENTS:        the present time.  We are working to refine the  
  COMMENTS:        position.  The source is also detected during a  
  COMMENTS:        pointing at the LOCBURST position, which indicates  
  COMMENTS:        the source is within one degree of the  
  COMMENTS:        LOCBURST position.  The measured flux is much   
  COMMENTS:        brighter than any catalogued X-ray source.  
  COMMENTS:        F.Marshall & T.Takeshima
  

• GCN/IPN alert
  

  TITLE:          GCN/IPN/HUNTSVILLE LOCALIZATION
  NOTICE_TYPE:    Updated (based on the BATSE-LOCBURST location)
  NOTICE_DATE:    Thu May  6 19:14:36 GMT 1999
  TRIGGER_NUM:    7549
  GRB_DATE:       99/05/06
  GRB_TIME:       11:23:30.93 UT
  BACO_RA:        176.72d {+11h 46m 52s}   (J2000)
  BACO_DEC:       -34.35d {-34d 21' 12"}
  HUNT_RA:        178.26d {+11h 53m 02s}   (J2000)
  HUNT_DEC:       -26.24d {-26d 14' 23"}
  HUNT_ERR:       2.02 [degees radius, statistical only]
  B_H_DELTA:      8.23 [deg]
  HUNT_SC_AZ:     217.84 [deg]
  HUNT_SC_EL:     -43.52 [deg]  {Zen_angle=133.52}
  SUN_POSTN:      43.04d {+02h 52m 09s}  +16.48d {+16d 28' 59"}(Current)
  SUN_B_DIST:     134.97 [deg]
  MOON_POSTN:     290.74d {+19h 22m 57s} -19.72d {-19d 43' 03"}(Current)
  MOON_B_DIST:    97.24 [deg]
  ANNULUS_RA:     144.9608d {+09h 39m 51s}   (J2000)
  ANNULUS_DEC:    -7.3258d {-07d 19' 32"}
  ANNULUS_RADIUS: 37.419 [deg]
  ANNULUS_WIDTH:  0.112 [deg]  (Total width)
  COMMENTS:       Duration ~150 sec.  Five separate peaks.  Strong.
  COMMENTS:       Seen above 300 keV.
  
  This IPN localization is preliminary.  The "total width" of the annulus
  was selected to include all known uncertainties and systematics. The final
  analysis will reduce this width. All follow-up queries should be addressed 
  to Kevin Hurley (UC Berkeley, khurley@sunspot.ssl.berkeley.edu).
  

• GCN notice #290
  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.
• GCN/RXTE alert
  

  TITLE:           GCN/RXTE_PCA BURST POSITION NOTICE
  NOTICE_DATE:     Thu 06 May 99 20:29:37 UT
  NOTICE_TYPE:     RXTE-PCA
  TRIGGER_NUM:     7549
  GRB_DATE:        11304 TJD;   126 DOY;   99/05/06
  GRB_TIME:        41010.94 SOD {11:23:30.94} UT
  GRB_RXTE_RA:     178.69d {+11h 54m 46s} (J2000),
                   178.68d {+11h 54m 44s} (current),
                   178.05d {+11h 52m 13s} (1950)
  GRB_RXTE_DEC:    -26.76d {-26d 45' 35"} (J2000),
                   -26.76d {-26d 45' 22"} (current),
                   -26.48d {-26d 28' 53"} (1950)
  GRB_RXTE_ERROR:  0.100 [deg radius, statistical only]
  GRB_RXTE_INTEN:  1.50 [mCrab]
  SUN_POSTN:        43.04d {+02h 52m 09s}  +16.48d {+16d 28' 59"}
  SUN_DIST:        137.73 [deg]
  MOON_POSTN:      290.74d {+19h 22m 57s}  -19.72d {-19d 43' 03"}
  MOON_DIST:        99.42 [deg]
  PROG_LEVEL:      3
  COMMENTS:        RXTE-PCA GRB Coordinates.  
  COMMENTS:        The RXTE-PCA observation started at 99/05/06 14:25:28 UT.  
  COMMENTS:        This is a preliminary determination of the position  
  COMMENTS:        assuming little variation in source intensity  
  COMMENTS:        between the RXTE scan at 16:00 and the scan at 16:20.  
  COMMENTS:        The position is consistent with the annulus  
  COMMENTS:        reported in the GCN/IPN Notice for GRB990506 (Trig=7549).  
  COMMENTS:        A later observation at 18:50 shows that the X-ray source  
  COMMENTS:        is dimming.  
  COMMENTS:        T.Takeshima & F.Marshall
  

• GCN notice #291
  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 and reproduced below.
• GCN notice #292
  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.
• GCN/RXTE alert
  

  TITLE:           GCN/RXTE_PCA BURST POSITION NOTICE
  NOTICE_DATE:     Fri 07 May 99 02:31:42 UT
  NOTICE_TYPE:     RXTE-PCA
  TRIGGER_NUM:     7549
  GRB_DATE:        11304 TJD;   126 DOY;   99/05/06
  GRB_TIME:        41010.94 SOD {11:23:30.94} UT
  GRB_RXTE_RA:     178.72d {+11h 54m 53s} (J2000),
                   178.71d {+11h 54m 51s} (current),
                   178.08d {+11h 52m 20s} (1950)
  GRB_RXTE_DEC:    -26.73d {-26d 43' 47"} (J2000),
                   -26.73d {-26d 43' 34"} (current),
                   -26.45d {-26d 27' 05"} (1950)
  GRB_RXTE_ERROR:  0.040 [deg radius, statistical only]
  GRB_RXTE_INTEN:  2.60 [mCrab]
  SUN_POSTN:        43.04d {+02h 52m 09s}  +16.48d {+16d 28' 59"}
  SUN_DIST:        137.76 [deg]
  MOON_POSTN:      290.74d {+19h 22m 57s}  -19.72d {-19d 43' 03"}
  MOON_DIST:        99.41 [deg]
  PROG_LEVEL:      3
  COMMENTS:        RXTE-PCA GRB Coordinates.  
  COMMENTS:        The RXTE-PCA observation started at 99/05/06 14:25:28.00 UT.  
  COMMENTS:        This is a refined determination of the position  
  COMMENTS:        using the data of addintional scans at around 18:50 UT.  
  COMMENTS:        The uncertainties of the position (90% confidence)  
  COMMENTS:        are 5.1 and 4.0 arcmin in R.A. and Dec., respectively.  
  COMMENTS:        (5.1 arcmin for R.A. is the actual angle.)  
  COMMENTS:        The source intensity decreased by factor of 2.4   
  COMMENTS:        between 16:10 and 18:50, which indicate the decay index  
  COMMENTS:        of -1.9 +/- 0.6 assuming a power-law decay.  
  COMMENTS:        Three more follow-up observations with RXTE/PCA  
  COMMENTS:        are scheduled in the following few days.  
  COMMENTS:        T.Takeshima & F.Marshall
  

• GCN notice #293
  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 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.
• GCN notice #294
  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 continuing in order to determine if this object is variable.
• GCN notice #295
  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.
• GCN notice #296
  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.
• GCN notice #297
  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.
• GCN notice #298
  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.
• GCN notice #305
  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.
• GCN notice #306
  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/
• GCN notice #308
  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.
• GCN notice #327
  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
  

• GCN notice #342
  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.
• GCN notice #350
  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.
• GCN notice #351
  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.
• GCN notice #352
  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.
• GCN notice #353
  H. Pedersen clarifies:
  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).
• from Taylor et al 2000 (astro-ph/0005379)
  
  Finding chart
  Radio light curve
• GCN notice #731
  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.
• Redshift measured by Caltech group to z = 1.3 (astroph/0102371)