TITLE: GCN CIRCULAR NUMBER: 7590 SUBJECT: GRB 080411: Swift-XRT Refined Analysis DATE: 08/04/12 13:27:11 GMT FROM: Olivier Godet at U.of Leicester O. Godet, A. P. Beardmore, K. Page (U. Leicester) reports on behalf the Swift-XRT team: The XRT began observing the field of GRB 080411 (trigger=309010, Marshall et al., GCN Circ. 7584) at 21:16:42 UT, 71 seconds after the BAT trigger. We analysed the first orbit of WT data (0.9 s) at T0+209s and the first 4 orbits of PC data (~3.6 ks) from T0+4.2ks to T0+17.4ks. The X-ray light-curve shows a broken power-law behaviour. Since there are no data between the WT and PC observations, it is difficult to constrain the initial decay and break time. The late decay from the PC data gives a decay slope of 0.98+/-0.05. Using ground data, we confirmed that the initial intense flux reported by Marshall et al. (GCN Circ. 7584) from the 0.1s image taken at T0+71s is real and is likely to correspond to the end of the activity observed in the BAT. That implies an initial rapid decay in the XRT light-curve. The WT spectrum contains only 20 counts. So, the fitting parameters are not well constrained when the spectrum is fitted by an absorbed power-law (N_H < 4.6e21 cm^-2 in excess with respect to the Galactic absorption along the burst line of sight (5.7e20 cm^-2, Kalberla et al. 2005) and a photon index of 2.85 +1.54/-1.05). The PC spectrum from T0+4.2ks to T0_17.4ks is fitted well by an absorbed power-law with a photon index of 2.14 +/- 0.09 and an absorption column of (1.5 +/- 0.3)e21 cm^-2, in excess with respect to the Galactic one. The observed (unabsorbed) flux in the 0.3-10 keV band is 7.1e-10 (1.7e-9) erg cm^-2 s^-1 for the WT spectrum and 7.2e-11 (1.1e-10) erg cm^-2 s^-1 for the PC spectrum. The predicted XRT count rate at T0+1d (T0+3d) is 0.26 (0.07) count s^-1, which corresponds to an observed 0.3-10 keV flux of 2.7e-11 (7.1e-12) erg cm^-2 s^-1. This is an official product of the Swift-XRT team.