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TITLE: GCN GRB OBSERVATION REPORT
NUMBER: 1907
SUBJECT: GRB 030227: fading of candidate optical afterglow 'S1-A'
DATE: 03/02/28 10:02:17 GMT
FROM: Alicia Soderberg at Caltech <ams@astro.caltech.edu>
A. M. Soderberg, D. Fox, S. Kulkarni, and E. Berger (Caltech) report on
behalf of a larger GRB collaboration:
"We have imaged the field of GRB 030227 with ESI on Keck II beginning
at Feb 28.242 UT in various optical bands. In the R-band image, we
find two sources in the 3-arcminute (radius) error circle of the XMM
source 'S1' (Loiseau et al. GCN 1901), hereafter S1-A and S1-B:
'S1-A' 04:57:33.05 +20:29:04.9 (J2000)
'S1-B' 04:57:32.80 +20:29:06.2 (J2000)
The positions are accurate to 0.3" and are based on 19 stars from the
GSC-II catalog.
The source S1-A is clearly seen in the Isaac Newton Telescope (INT)
R-band image presented by Castro-Tirado et al. (GCN 1904). We find a
magnitude of R ~ 23.5 for S1-A and R ~ 25.0 for S1-B relative to the
above set of GSC-II stars. Comparison with Castro-Tirado et al. (GCN
1904) indicates that the source has faded by ~1.0 magnitudes since
Feb. 27.872 UT. This fading is visually confirmed by comparing our
image (see URL below) with the INT image. We note that the candidate
of Ofek and Gal-Yam (GCN 1903) may also be fading; with the same
calibration we measure R ~ 22.1 for their source and R ~ 18.1 for
their star A.
Given the coincidence of S1-A with the X-ray source and its fading
behavior we suggest that it is the optical afterglow of GRB 030227.
Our image can be found at:
http://www.astro.caltech.edu/~ams/grb030227/
Analysis of other candidates is in progress."
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