TITLE: GCN CIRCULAR NUMBER: 11927 SUBJECT: GRB 110411A: Swift-XRT refined Analysis DATE: 11/04/12 16:26:11 GMT FROM: Dirk Grupe at PSU/Swift-XRT D. Grupe (PSU) reports on behalf of the Swift-XRT team: We have analyzed 11 ks of XRT data for GRB 110411A (Grupe et al. GCN Circ. 11918), from 117 s to 37.2 ks after the BAT trigger. The data comprise 64 s in Windowed Timing (WT) mode (the first 8 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Goad et al. (GCN. Circ 11920). The light curve can be modeled with a series of power-law decays. The initial decay index is alpha=6.0 (+/-0.6). At T+230 s the decay flattens to an alpha of 0.58 (+0.11, -0.12) before breaking again at T+4446 s to a final decay with index alpha=1.39 (+0.27, -0.24). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.93 (+0.23, -0.21). The best-fitting absorption column is 1.02 (+0.14, -0.12) x 10^22 cm^-2, in excess of the Galactic value of 6.9 x 10^20 cm^-2 (Kalberla et al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.0 x 10^-11 (2.3 x 10^-10) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.02 (+0.14, -0.12) x 10^22 cm^-2 Galactic foreground: 6.9 x 10^20 cm^-2 Excess significance: 13.5 sigma Photon index: 2.93 (+0.23, -0.21) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00451165. With an excess absorption column density of 9.5 x 10^21 cm^-2 following the relation in Grupe et al. (2007, AJ, 133, 2216) the estimated maximum redshift of the afterglow is z < 1.0. This circular is an official product of the Swift-XRT team.