GRB 990506

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.

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
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  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.

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
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  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.

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."

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
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 ) 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.

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
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 ) 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
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 ). 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."

J. P. Halpern reports (from his office) that an optical object referred
to in GCN #294
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  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.

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
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 ) 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
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 ).

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.

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.

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
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 ).  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.

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
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 )
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
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 ) 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.

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
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 ) 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.

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
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 ), 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.

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
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 ) 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
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 ), 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
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 ) and Garnavich et al. (GCN #302
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 ) 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.]

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.

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
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 ) 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.]

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
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 ) 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."

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
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 ) 
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
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 ) 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."

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
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 ), 
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.

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
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 ) within the RXTE/IPN localization (GCN 298
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 ) 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.

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
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 ) 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
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 ) 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
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 ), 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."

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
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 ) 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
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 ), 
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."

It has come to my attention that the phrasing of GCN 352
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  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
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 ).

                                        Holger Pedersen

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
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 ) 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.