TITLE: GCN CIRCULAR NUMBER: 43275 SUBJECT: GRB 251230A: Swift-XRT refined Analysis DATE: 25/12/31 01:48:14 GMT FROM: Phil Evans at U of Leicester <pae9@star.le.ac.uk> T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), D.N. Burrows (PSU), S. Lanava (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 5.6 ks of XRT data for GRB 251230A, from 92 s to 50.9 ks after the trigger. The data comprise 329 s in Windowed Timing (WT) mode (the first 6 s were 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=7.1 (+/-0.5). At T+129 s the decay flattens to an alpha of 0.2 (+0.3, -1.1) before breaking again at T+194 s to a final decay with index alpha=1.51 (+/-0.05). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.80 (+/-0.06). The best-fitting absorption column is 4.4 (+1.3, -1.2) x 10^20 cm^-2, in excess of the Galactic value of 1.9 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.82 (+/-0.14) and a best-fitting absorption column of 5.7 (+3.6, -3.2) x 10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x 10^-11 (4.1 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 5.7 (+3.6, -3.2) x 10^20 cm^-2 Galactic foreground: 1.9 x 10^20 cm^-2 Excess significance: 2.0 sigma Photon index: 1.82 (+/-0.14) If the light curve continues to decay with a power-law decay index of 1.51, the count rate at T+24 hours will be 2.3 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.4 x 10^-14 (9.4 x 10^-14) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/01429020. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/43275. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...