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GCN Circular 316

GRB990510 optical observations
1999-05-11T13:06:28Z (25 years ago)
Andrzej Udalski at Warsaw U. Observatory <>
G. Pietrzynski and A. Udalski (Warsaw University Observatory) report on
behalf of the OGLE microlensing survey team:

We monitored the optical counterpart of GRB 990510 (Vreeswijk et al.
1999, GCN 310) starting on May 10.992 UT, 1999 with the 1.3-m Warsaw
telescope at the Las Campanas Observatory (Chile). In total 17 V-band,
21 I-band frames were collected, covering about 10.25 hours. Exposure
time was 900 sec and 600 sec for the V and I-band frames, respectively.
The object is apparently variable -- its brightness faded by about 0.6
mag in the course of the night: from 19.45. to 20.05 in the V band and
18.50 to 19.15 in the I-band. Standard VI photometry of three, well
separated nearby constant stars (uncertainty +/-0.03 mag) is:

         Delta X  Delta Y   \alpha_2000  \delta_2000     V       I
         from GRB position

Star 1     33.4"E  43.9"S   13:38:20.56  -80:30:31.9   15.617  14.636   
Star 2     59.8"W  21.0"N   13:37:43.48  -80:29:26.7   16.203  15.161
Star 3     16.5"W  36.7"N   13:38:00.82  -80:29:11.5   17.014  16.094

Photometry of the optical counterpart of GRB 990510 and light curves are
available from the OGLE Internet archive:

[GCN OP NOTE:  This circular was received at 12:42 11 May 99 UT,
but was not distributed due to not having a prior vetted account.]
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