TITLE: GCN CIRCULAR NUMBER: 13187 SUBJECT: GRB 120401A: Swift-XRT refined Analysis DATE: 12/04/01 17:34:05 GMT FROM: Phil Evans at U of Leicester P.A. Evans (U. Leicester), O.M. Littlejohns (U. Leicester), A. Maselli (INAF-IASFPA), V. Mangano (INAF-IASFPA), A. Melandri (INAF-OAB), J.A. Kennea (PSU), M.C. Stroh (PSU), D.N. Burrows (PSU) and A.P. Beardmore report on behalf of the Swift-XRT team: We have analysed 10 ks of XRT data for GRB 120401A (Beardmore et al. GCN Circ. 13182), from 124 s to 24.8 ks after the BAT trigger. The data comprise 519 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Evans et al. (GCN. Circ 13183). The late-time light curve (from T0+5.0 ks) can be modelled with a power-law decay with a decay index of alpha=1.2 (+0.4, -0.3). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.29 (+0.07, -0.06). The best-fitting absorption column is 1.27 (+0.13, -0.12) x 10^21 cm^-2, in excess of the Galactic value of 3.2 x 10^20 cm^-2 (Kalberla et al. 2005). The PC mode spectrum has a photon index of 1.75 (+0.11, -0.10) and a best-fitting absorption column consistent with the Galactic value. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.0 x 10^-11 (4.3 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 0 (+1.5, -0) x 10^20 cm^-2 Galactic foreground: 3.2 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.75 (+0.11, -0.10) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00519043. This circular is an official product of the Swift-XRT team.