GCN Circular 11989
A. Melandri, P. D'Avanzo, R. Margutti (INAF-OAB), B. Sbarufatti (INAF- OAB/IASFPA) report on behalf of the Swift Team: Swift continued to monitor the field of GRB 110428A (Vasileiou et al., GCN 11982) in two different observations carried out on April 29th and May 1st, 2011. In the final 18.49 ks of data (at a mean T-T0 = 2.07 days after the burst event) we still detect Source #1 reported by Melandri et al. (GCN 11984) with count rate of (1.6e-2 +/- 1.1e-3) cts/s, consistent with a constant flux for this source. Source #2 is no longer detected with a 3 sigma upper limit of 1.4e-3 cts/s. The probability for this source of having a constant flux is 8e-6. This is evidence of the fading of Source #2 with respect to the XRT observation reported in Melandri et al. (GCN 11984). Therefore we consider Source #2 as the X-ray afterglow of GRB 110428A. This circular is an official product of the Swift-XRT team.