Circular No. 7100
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
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GRB 990123
     C. W. Akerlof and T. A. McKay, University of Michigan, report
on behalf of the ROTSE collaboration (Michigan/Los Alamos National
Laboratory/Lawrence Livermore National Laboratory):  "We observed
the error box of GRB 990123 provided by the BACODINE Burst Position
Notice (dated 23-Jan-99 09:46:59) using the ROTSE-I telephoto
camera array located at Los Alamos.  The first exposure began at
9h47m18s.30 UT (Jan. 23.407851), or 22.18 s after the nominal burst
trigger time.  A rapidly fading object was discovered at R.A. =
15h25m30s.1, Decl. = +44o46'00" (equinox 2000.0), which is within
one-third of a pixel of the optical counterpart reported by Odewahn
et al. (IAUC 7094).  The lightcurve for this object is relatively
complex: the luminosity increases by 3 magnitudes between the first
and second exposures.  Exposure times and estimated V magnitudes
for the first six exposures are as follows:  Jan. 23.407851, 5 s,
11.82; 23.408142, 5, 8.95; 23.408435, 5, 10.08; 23.410851, 75,
13.22; 23.412764, 75, 14.00; 23.414677, 75, 14.53.  Note that the
ROTSE-I detector system uses an unfiltered broadband CCD, so that
magnitude estimates are based on comparisons to catalogue values
for nearby stars.  Sky-patrol images of the same coordinates taken
133 min earlier showed no evidence of the transient to a limit of
at least 2 mag deeper.  A more extensive analysis of these data
will be available in the near future.  The discovery images are
posted on the ROTSE Web page at:
http://www.umich.edu/~rotse/gifs/grb990123/990123.gif."
     J. Zhu, J. S. Chen, and H. T. Zhang, Beijing Astronomical
Observatory (BAO), report that an observation on Jan. 24.730-24.861
UT with the BAO 0.6-m Schmidt telescope under nonphotometric
conditions (two 60-min images taken with a BATC i-band filter;
central wavelength 666.0 nm, bandwidth 48.0 nm) gives a magnitude
of 21.0 +/- 0.3 (Jan. 24.818) for the transient + presumed host
galaxy, using stars 1 and 2 from GCN 204
(http://gcn.gsfc.nasa.gov/gcn/gcn3/204.gcn3).  No visual separation
between the optical transient and host galaxy could be recognized
because of the low S/N ratio and bad spatial resolution (1 pixel =
1".7; seeing 5".6).  The CCD image is available at
http://vega.bac.pku.edu.cn/~zj/grb/grb990123.html.  A 40-min
exposure on Jan. 25.901 yields a magnitude of 21.3 +/- 0.3 (near
the detection limit), suggesting that by this time they were only
detecting the the coincident galaxy that was found on the digital
sky-survey image by Odewahn et al. (IAUC 7094).

                      (C) Copyright 1999 CBAT
1999 January 26                (7100)            Daniel W. E. Green