{
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "body": "C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB),\nJ.A. Kennea (PSU), D.N. Burrows (PSU), M. A. Williams (PSU), A.P.\nBeardmore (U. Leicester), J.P. Osborne (U. Leicester) and P.A. Evans\nreport on behalf of the Swift-XRT team:\n\nWe have analysed 6.9 ks of XRT data for GRB 250424A, from 259 s to 18.9\nks after the  BAT trigger. The data are entirely in Photon Counting\n(PC) mode. \n\nThe light curve can be modelled with a series of power-law decays. The\ninitial decay index is alpha=0.20 (+0.12, -0.13). At T+2382 s  the\ndecay steepens to an alpha of 0.53 (+0.16, -0.11) before breaking again\nat T+17.4 ks to a final decay with index alpha=4.5 (+3.5, -2.8).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 2.05 (+/-0.11). The\nbest-fitting absorption column is  1.04 (+0.11, -0.10) x 10^22 cm^-2,\nin excess of the Galactic value of 6.4 x 10^20 cm^-2 (Willingale et al.\n2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion\nfactor deduced from this spectrum  is 4.9 x 10^-11 (9.6 x 10^-11) erg\ncm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     1.04 (+0.11, -0.10) x 10^22 cm^-2\nGalactic foreground: 6.4 x 10^20 cm^-2\nExcess significance: 15.7 sigma\nPhoton index:\t     2.05 (+/-0.11)\n\nIf the light curve continues to decay with a power-law decay index of\n4.5, the count rate at T+24 hours will be 5.3 x 10^-4 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.6 x\n10^-14 (5.1 x 10^-14) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/01306404.\n\nThis circular is an official product of the Swift-XRT team.\n",
  "bibcode": "2025GCN.40233....1S",
  "circularId": 40233,
  "eventId": "GRB 250424A",
  "subject": "GRB 250424A: Swift-XRT refined Analysis",
  "submittedHow": "email",
  "createdOn": 1745503157904
}