TITLE: GCN CIRCULAR NUMBER: 1857 SUBJECT: GRB030131: Candidate Optical Afterglow DATE: 03/02/05 07:13:26 GMT FROM: Derek Fox at CIT 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."