TITLE: GCN CIRCULAR NUMBER: 36538 SUBJECT: GRB 240523A: Swift-XRT refined Analysis DATE: 24/05/24 00:30:09 GMT FROM: Phil Evans at U of Leicester <pae9@star.le.ac.uk> R. Brivio (INAF-OAB), D.N. Burrows (PSU), J. D. Gropp (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAR) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.5 ks of XRT data for GRB 240523A, from 132 s to 27.6 ks after the BAT trigger. The data comprise 8 s in Windowed Timing (WT) mode (taken while Swift was slewing), with the remainder in Photon Counting (PC) mode. The light curve can be modelled with a series of power-law decays. The initial decay index is alpha=2.8 (+0.6, -0.4). At T+400 s the decay flattens to an alpha of -0.4 (+0.3, -0.5) before breaking again at T+2137 s to a final decay with index alpha=1.41 (+0.26, -0.24). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.06 (+0.24, -0.22). The best-fitting absorption column is 1.1 (+0.6, -0.5) x 10^21 cm^-2, in excess of the Galactic value of 1.6 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.3 x 10^-11 (4.2 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.1 (+0.6, -0.5) x 10^21 cm^-2 Galactic foreground: 1.6 x 10^20 cm^-2 Excess significance: 2.9 sigma Photon index: 2.06 (+0.24, -0.22) If the light curve continues to decay with a power-law decay index of 1.41, the count rate at T+24 hours will be 2.0 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.5 x 10^-14 (8.2 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/01230423. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/36538. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...