TITLE: GCN CIRCULAR NUMBER: 10899 SUBJECT: GRB 100628A: Swift XRT detection of a possible X-ray afterglow DATE: 10/06/28 20:24:02 GMT FROM: Rhaana Starling at U of Leicester R.L.C. Starling (U. Leicester) and S. Immler (CRESST/GSFC/UMD) report on behalf of the Swift-XRT team: We have analysed 8.7 ks of XRT data for GRB 100628A (Immler et al. GCN Circ. 10895), from 93 s to 18.8 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. A source is detected at the 3-sigma confidence level within the BAT refined error circle (Barthelmy et al. GCN Circ. 10896) at the position: RA (J2000) = 15 03 52.95 Dec (J2000) = -31 39 41.7 with an error of 5.2 arcsec (radius, 90% containment). This is 91.8 arcsec from the BAT refined position. The possible source has a count rate of 0.0023+/-0.0007 count/s. We cannot determine whether the source is fading at this time. This circular is an official product of the Swift-XRT team.