TITLE: GCN CIRCULAR NUMBER: 36956 SUBJECT: GRB 240727A: Swift-XRT refined Analysis DATE: 24/07/27 20:27:35 GMT FROM: Phil Evans at U of Leicester <pae9@star.le.ac.uk> J. D. Gropp (PSU), S. Dichiara (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), J.A. Kennea (PSU) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.6 ks of XRT data for GRB 240727A, from 109 s to 51.8 ks after the BAT trigger. The data comprise 377 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 light curve can be modelled with an initial power-law decay with an index of alpha=0.89 (+0.26, -0.58), followed by a break at T+177 s to an alpha of 1.80 (+0.06, -0.05). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.98 (+/-0.06). The best-fitting absorption column is 1.46 (+0.19, -0.18) x 10^21 cm^-2, in excess of the Galactic value of 3.6 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.25 (+0.14, -0.12) 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 5.3 x 10^-11 (5.4 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.6 (+3.6, -0.0) x 10^20 cm^-2 Galactic foreground: 3.6 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.25 (+0.14, -0.12) If the light curve continues to decay with a power-law decay index of 1.80, the count rate at T+24 hours will be 4.8 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.5 x 10^-14 (2.6 x 10^-14) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01245074. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/36956. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...