TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5110 SUBJECT: GRB060510B: Swift XRT refined analysis DATE: 06/05/10 22:07:59 GMT FROM: Matteo Perri at ISAC/ASDC M. Perri, M. Capalbi, M.L. Conciatore, L. Vetere (ASDC), H.A. Krimm (GSFC/USRA) and D.N. Burrows (PSU) report on behalf of the Swift/XRT team: We have analyzed the first four orbits of Swift XRT data on the BAT GRB 060510B (Krimm, et al., GCN 5096; Barthelmy et al., GCN 5107). A 5.3 ks Photon Counting (PC) mode image gives a refined X-ray position of: RA(J2000) = 15h 56m 29.9s Dec(J2000) = +78d 34' 09.7" with an uncertainty of 3.6 arcsec (90% containment). This is 2 arcmin away from the center of the refined BAT position quoted in GCN 5107, and 1.8 arcsec away from the initial XRT position reported in GCN 5096. The early 0.3-10 keV light curve has a complex behavior. The first orbit of data shows an initial shallow decay with slope ~ -0.3, a temporal break at about T+350s followed by a steep decay with slope ~ -11. Three X-ray flares at about T+200s, T+300s and T+880s are also observed during the first orbit. The afterglow decay between the second and the fourth orbit has a slope of ~ -0.4. The X-ray spectrum covering the time period from T+128s to T+456s is well fit by an absorbed power-law with a photon index of 1.42+/-0.13 and column density of (1.5+/-0.1)e21 cm**-2. We note the Galactic column density in the direction of the source is 3.8e20 cm**-2. The observed (unabsorbed) 0.3-10 keV flux for this spectrum is 4.3e-9 (4.9e-9) erg/cm**2/s. All the quoted errors are at the 90% confidence level. If the burst continues decaying at the current rate we estimate an XRT count rate of 6e-3 counts/s at T+24hr, which corresponds to an unabsorbed 0.3-10.keV flux of 3e-13 ergs cm**-2 s**-1. This circular is an official product of the Swift XRT Team.