TITLE: GCN CIRCULAR NUMBER: 6200 SUBJECT: GRB 070309: variability of the XRT afterglow candidate DATE: 07/03/12 17:02:35 GMT FROM: Cristiano Guidorzi at INAF-OAB S.D. Vergani (Dunsink observatory-DIAS, DCU), P. Romano (INAF-OAB, Univ. Bicocca), C. Guidorzi (INAF-OAB, Univ. Bicocca), A. Moretti (INAF-OAB) report on behalf of the Swift-XRT team: We continued to analyse the XRT data regarding the source reported by Vergani et al. in GCN Circ. 6187. We collected a total of 21 counts for a total exposure time of about 17ks. It is not possible to extract a proper light curve or spectrum. We divided the observations in two consecutive blocks, with exposures of 7672 s and of 9623 s, collecting 16 and 5 counts, respectively. In the assumption of a constant rate source, the probability of having equally or less uniformly distributed counts is estimated to be smaller than 1%. We conclude that this seems to be a varying source but at the present time we cannot confirm that this is the X-ray afterglow of GRB070309. This Circular is an official product of the Swift XRT Team.