GCN Circular 11984
A. Melandri, P. D'Avanzo, R. Margutti (INAF-OAB), B. Sbarufatti (INAF- OAB/IASFPA) and M. Stamatikos (OSU/NASA/GSFC) report on behalf of the Swift Team: At 00:47 UT, April 29th, 2011, Swift began a Target of Opportunity observation of the Fermi GBM/LAT discovered burst GRB 110428A (Vasileiou et al. GCN 11982), ~55.6 ks after the Fermi detection. In 4.8 ks of Photon Counting mode data, we detect two sources within the Fermi-LAT error circle (0.15 deg radius, 68% CL) at the following positions: Source 1: RA(J2000): 00 21 50.47 Dec(J2000): +64 48 52.4 with an uncertainty of 4.6 arcsec. Source 2: RA(J2000): 00 22 22.22 Dec(J2000): +64:50:57.1 with an uncertainty of 7.1 arcsec. Uncertainty radii are given at 90% containment. We note that the position of Source 1 is consistent with a known ROSAT source (1RXS J002150.5+644850) also present in the DSS. Source 2 is an uncatalogued object. The two sources have a count rate of about (1.2e-2 +/- 1.8e-3) and (2.9e-3 +/- 9.1e-4) cts/s, respectively. It is not possible to determine whether these sources are fading given the current statistics. Further Swift-XRT observations of the field are planned. We encourage ground-based follow-up observations. This circular is an official product of the Swift-XRT team.