[vsnet-grb-info 726] GRB030131: Candidate Optical Afterglow

[GCN Circulars <gcncirc@lheawww.gsfc.nasa.gov>]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1857
SUBJECT: GRB030131: Candidate Optical Afterglow
DATE:    03/02/05 07:13:26 GMT
FROM:    Derek Fox at CIT  <derekfox@astro.caltech.edu>

D.W. Fox (Caltech), P.A. Price (RSAA/ANU), T. Herter (Cornell),
P. Appleton (IPAC), and G. Cotter (Cambridge) report on behalf of a
larger collaboration:

"We have observed the full corrected localization region (GCN 1847)
for GRB030131 with the 60-inch telescope on Mt. Palomar (P60), for
roughly 15 min each in Gunn r and i on the night of 4 Feb 2003 UT.  We
have also observed a portion of this region with the 200-inch Hale
telescope + COSMIC (P200), for 30 min in R band on the night of 1 Feb
2003 UT (mean epoch 10:27 UT, or 26.8 hours post-burst).

"Visual comparison of the P60 images with our summed 48-inch + NEAT
(P48) image from 31 Jan 2003 UT (mean epoch 11:16 UT, or 3.62 hours
post-burst; c.f. GCN 1850) reveals a point-like source in the P48
image that is not present in the P60 images.  The unfiltered P48
magnitude of this source, R~21.2 by reference to four nearby USNO-A2.0
stars, is near the limit of the P60 r image.  However, the source lies
within the field of view of the P200 R-band image, and is barely
detected with R>~23.5 at that time.

"The coordinates of the source relative to the GSC-II are:

    RA 13:28:22.29, Dec +30:40:23.7  (J2000)

with an uncertainty of less than 1" in each coordinate.  Inspection of
the individual P48 images reveals that the source is present at the
same position in each image (mean epochs 10:43 to 11:32 UT, 31 Jan
2003).  The brightness of the source in the various images is roughly
constant, to within about one magnitude, although we observe possible
variability of the source within this range.

"We tentatively suggest that this source is the afterglow of
GRB030131.  We consider this identification provisional in the absence
of further supporting observations."

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