TITLE: GCN CIRCULAR NUMBER: 13514 SUBJECT: GRB 120724A: Swift-XRT refined Analysis DATE: 12/07/24 18:50:07 GMT FROM: Phil Evans at U of Leicester P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. Maselli (INAF-IASFPA), J.A. Kennea (PSU), M.C. Stroh (PSU), D.N. Burrows (PSU), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), and O.M. Littlejohns (U. Leicester) report on behalf of the Swift-XRT team: We have analysed 6.4 ks of XRT data for GRB 120724A (D'Avanzo et al. GCN Circ. 13510), from 115 s to 13.0 ks after the BAT trigger. The data comprise 40 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The best available XRT position (using the promptly downlinked event data, the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue) is RA, Dec = 245.1800, 3.5081 which is equivalent to: RA (J2000): 16 20 43.19 Dec(J2000): +03 30 29.0 with an uncertainty of 2.2 arcsec (radius, 90% confidence). The light curve can be modelled with an initial power-law decay with an index of alpha=2.78 (+/-0.22), followed by a break at T+851 s to an alpha of 0.48 (+0.18, -0.79). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.88 (+0.20, -0.09). The best-fitting absorption column is consistent with the Galactic value of 4.3 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 3.7 x 10^-11 (4.1 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Galactic foreground: 4.3 x 10^20 cm^-2 Intrinsic column: 0 (+9.3, -0) x 10^20 cm^-2 at z=1.48 Photon index: 1.88 (+0.20, -0.09) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00528443. This circular is an official product of the Swift-XRT team.