GCN Circular 7532
M. Perri and G. Stratta (ASDC) report on behalf of the Swift XRT team: We have analysed the first 3 orbits of Swift XRT data of the BAT GRB 080328 (Perri et al., GCN Circ. 7525). The data consist of 151 s in Windowed Timing (WT) mode, from T+108s to T+259s, and of 6.9 ks in Photon Counting (PC) mode thereafter. The best XRT position is the UVOT-enhanced position reported by Beardmore et al. (GCN Circ. 7527). The early 0.3-10 keV X-ray light curve in WT mode shows a rapid decay. Starting from T+260s up to T+13.7ks the curve is well fit by a broken power-law model with decay indices alpha1=-0.57 (+0.09) (-0.06), alpha2=-1.10 (+/-0.05) and a temporal break at (1.7+/-0.3) ks. The WT X-ray spectrum is well fit by an absorbed power-law model with a photon index of 2.1 (+/-0.1), a column density of (4.2+/-0.4)e21 cm**-2 and an average observed 0.3-10 keV flux of 9.3e-10 erg/cm**2/s. The PC X-ray spectrum during the first orbit, from T+260s to T+2106s, is also well fit by an absorbed power-law model with a photon index of 2.2 (+/-0.1) and a column density of (5.0+/-0.6)e21 cm**-2. The observed 0.3-10 keV flux for this spectrum is 1.5e-10 erg/cm**2/s. We note the Galactic column density in the direction of the source is 3.4e21 cm**-2. Assuming the X-ray emission continues to decline at the same rate, we predict a 0.3-10 keV XRT count rate of 0.03 count/s at T+24hr, which corresponds to an observed 0.3-10 keV flux of about 1.4e-12 erg/cm**2/s. This circular is an official product of the Swift XRT Team.