TITLE: GCN CIRCULAR NUMBER: 6002 SUBJECT: GRB 070107: Possible UVOT Afterglow DATE: 07/01/08 20:05:22 GMT FROM: Padi Boyd at GSFC GRB 070107: Possible UVOT Afterglow P. T. Boyd (GSFC), M. Chester (PSU), C. B. Markwardt (CRESST/GSFC/USRA) and F. E. Marshall (GSFC) report on behalf of the Swift team: In response to GRB 070107 (Stamatikos et al. GCN Circ. 5999) UVOT took a 100-s finding chart exposure with the White filter (160-650 nm) starting 183 seconds after the BAT trigger, followed by a 400-s V finding chart exposure. A second set of finding chart exposures was obtained starting 868s post-trigger. We detect a new variable source inside the XRT error region (Kennea et al. GCN Circ. 6000) in the first exposure at RA(J2000) = 10 37 36.35 DEC(J2000) = -53 12 47.5 with a 1-sigma error radius of about 1 arcsec. However, we caution that this source is in a crowded region at low galactic latitude, and only 4.1 arcsec from a bright V=15.9 cataloged star, which causes the afterglow and the star to be blended in the UVOT image, and complicates the position, magnitude, and significance estimates. We estimate a White magnitude of ~19.5 for the new source. The source is detected at a ~4-sigma significance level. The same source is detected at a level of 2.7 sigma in the subsequent 400-s V finding chart. The new source is not significant in later White and V exposures. We note that the extinction estimate in this region (whose galactic latitude is 4.56 degrees) is large, and uncertain.