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GCN Circular 1907

Subject

GRB 030227: fading of candidate optical afterglow 'S1-A'

Date

2003-02-28T10:02:17Z (22 years ago)

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 1901Not found
 
 
), 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 1904Not found
 
 
).  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
1904Not found
 
 
) 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 1903Not found
 
 
) 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."