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GCN Circular 314

GRB 990510 optical observations
1999-05-11T05:31:52Z (25 years ago)
Krzysztof Z. Stanek at CfA <>
J. Kaluzny (Warsaw Univ. Obs.), P. M. Garnavich, K. Z. Stanek
(Harvard-Smithsonian CfA), W. Pych (Warsaw Univ. Obs.) and I. Thompson
(Carnegie Obs.) report:

We measured the object at RA 13:38:07.64, Decl -80:29:48.8 (J2000)
(coordinates based on the GSC catalog), reported by Vreeswijk et
al. (GCN 310) to be a possible optical counterpart to GRB 990510 in
our R-band images taken with the 1.0-meter Swope telescope at the Las
Campanas Obs.  We find that the object declined by 0.34 mag over 4.6
hours beginning May 10.995 (UT) in the R-band.  The data is consistent
with a power-law decline with decay index of 0.89, obtained by fitting
combined data of Galama et al. (GCN 313) and ours.  The comparison
star (end figures of 00.82, 11.7) assumed by Galama et al. to be
R=17.2 is actually given in the USNO A2.0 catalog as R=16.5. We find
the R magnitudes in this region of the USNO catalog to be of dubious
quality, especially fainter than 16.5.  It is important to obtain an
independent photometric calibration for this field.

Adding seven 300s exposures in R with approximately 1" seeing reveals
an object 1.8" south of the OT and about 3 magnitudes fainter which
may be the host galaxy.

Compared to nearby field stars, the OT appears significantly
bluer by approximately 0.4 mag in V-R color.

The R-band lightcurve and the combined image of the field are
available at

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