TITLE: GCN CIRCULAR NUMBER: 9107 SUBJECT: GRB 090407: Swift-XRT refined analysis DATE: 09/04/08 00:10:35 GMT FROM: Andy Beardmore at U Leicester A.P. Beardmore (U. Leicester) and H. Ziaeepour (UCL-MSSL) report on behalf of the Swift-XRT team: We have analysed the first five orbits of Swift-XRT data obtained from GRB 090407 (trigger #348650; Ziaeepour, et al., GCN Circ. 9101), comprising 273 s taken in Windowed Timing (WT) mode, starting at T+96.7 s, followed by 10.2 ks in Photon Counting (PC) mode from T+398 s to T+24.2 ks. The UVOT-enhanced position was given by Evans et al. (GCN Circ. 9105). The 0.3-10 keV X-ray light curve shows a number of flares in the first 400 s, the largest occurring from T+120 s to T+180 s, reaching a peak rate of 90 count s^-1 at T+140 s. This flare is also seen by the Swift-BAT (Ukwatta et al., GCN Circ. 9104). Further flaring is seen from ~T+200s to ~T+350 s, ending with a steep decay of slope ~4.0. After T+950 s the X-ray light curve breaks to a much shallower decay slope of 0.28 +/- 0.06. The data show spectral evolution during the flaring intervals, after which the PC mode spectrum can be modelled by an absorbed powerlaw with a photon index of 2.43 +/- 0.13 and a total absorbing column density of (2.51 +/- 0.35) x 10^21 cm^-2, which is in excess of the Galactic value of 3.7 x 10^20 cm^-2 (Kalberla et al. 2005) in the direction of the burst. The observed 0.3-10 keV flux at this time (~T+6.2 ks) is (6.29 +0.41 -0.56) x 10^-12 erg cm^-2 s^-1, which corresponds to an unabsorbed flux of 1.3 x 10^-11 erg cm^-2 s^-1. The count to observed flux conversion factor for this spectrum is 3.5 x 10^-11 erg cm-^2 count^-1. If the light curve continues to decay with the same slope of 0.28 we predict an X-ray count rate of 0.047 count s^-1 at T+24 hours after the trigger, which corresponds to an observed 0.3-10 keV flux of 1.6 x 10^-12 erg cm^-2 s^-1. However, we note that it is unlikely the light curve decay will remain this shallow at T+24 hours. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_curves/00348650. This circular is an official product of the Swift-XRT team.