GCN Circular 1562
Subject
GRB 020903: Optical observations at RIKEN
Event
Date
2002-10-01T11:18:09Z (23 years ago)
From
Ken ichi Torii at RIKEN <torii@crab.riken.go.jp>
K. Torii (RIKEN) and H. Yamaoka (Kyushu Univ.) report:
The entire WXM error circle of XRF 020903 (Ricker, et al. GCN 1530)
was observed at RIKEN with the 0.25-m reflector equipped with
unfiltered cooled CCD AP6E. The observation started at 2002 September
3.6479 UT (5.23 hours after the burst trigger) and 20-s exposures were
repeated.
The first 168 frames, obtained between 3.6479 and 3.6965 UT, have
been stacked and inspected for the variable source (hereafter VS)
found by Soderberg, et al. (GCN 1554). In our image (4".2/pixel) a
spatially unresolvable source is detected at (R.A., Dec.) =
(22:48:42.37, -20:46:13.0) (J2000). The position is derived by using
12 comparison stars from UCAC1 and the fitting error is 0".3 in both
coordinates. This position is closer to the galaxy G2 (as tabulated in
USNO-A2.0) rather than to the VS.
We also find that the flux for the spatially unresolved G2+VS was
2.0+/-0.2 mag fainter than the star 1 in the finding chart of
Soderberg et al. (GCN 1554), which is consistent with the magnitude
difference (G2 - star 1 = +2.17) in GSC-2.2.1 F magnitude. These
results, both astrometrically and photometrically, show that the VS
was much fainter than the galaxy G2 during our observation.
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