TITLE: GCN CIRCULAR NUMBER: 6789 SUBJECT: GRB 070913: Swift-XRT detection of the possible X-ray afterglow DATE: 07/09/14 15:05:49 GMT FROM: Andy Beardmore at U Leicester A.P. Beardmore, K.L. Page (U. Leicester) and C. B. Markwardt (CRESST/GSFC/UMD) report on behalf of the Swift-XRT team. The Swift-XRT began observing the field of the BAT GRB 070913 (trigger #290843) at 2007-09-13T21:30, 75.2 ks after the BAT trigger (Markwardt et al., GCN 6782). In 8 orbits of photon counting mode data totalling 7.8 ks we find a faint, uncatalogued source inside the refined BAT error circle (Sato et al., GCN 6786) at RA, Dec (J2000) 228.75715, -24.29302, which is RA(J2000) = 15h 15m 01.7s Dec(J2000) = -24d 17' 34.9" with an uncertainty of 6.5 arcsec (radius, 90 percent confidence, including boresight uncertainties). The source is 5.7 arcsec away from the TAROT optical afterglow candidate reported by Klotz et al. (GCN 6787). The source has an observed 0.3-10.0 keV count rate of (1.4+/-0.5)e-3 count/s. We note the presence of a second faint X-ray source with a count rate of (1.3+/-0.5)e-3 count/s at RA, Dec (J2000) 228.70481, -24.21053, i.e. RA(J2000) = 15h 14m 49.2s Dec(J2000) = -24d 12' 37.9" with an uncertainty of 6.6 arcsec (radius, 90 percent confidence, including boresight uncertainties). This is 4.4 arcmin from the refined BAT position, and outside its 1.7 arcmin error radius. It is impossible to say whether either of the sources are fading at this stage, though the association of the first one with the fading optical object makes it the most likely candidate for the GRB X-ray afterglow. This circular is an official product of the Swift-XRT team.