{
  "circularId": 43275,
  "body": "T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M.G. Bernardini\n(INAF-OAB), D.N. Burrows (PSU), S. Lanava (PSU), S. Dichiara (PSU),\nJ.P. Osborne (U. Leicester), K.L. Page (U. Leicester) and P.A. Evans\nreport on behalf of the Swift-XRT team:\n\nWe have analysed 5.6 ks of XRT data for GRB 251230A, from 92 s to 50.9\nks after the   trigger. The data comprise 329 s in Windowed Timing (WT)\nmode (the first 6 s were taken while Swift was slewing) with the\nremainder in Photon Counting (PC) mode. \n\nThe light curve can be modelled with a series of power-law decays. The\ninitial decay index is alpha=7.1 (+/-0.5). At T+129 s  the decay\nflattens to an alpha of 0.2 (+0.3, -1.1) before breaking again at T+194\ns to a final decay with index alpha=1.51 (+/-0.05).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.80 (+/-0.06). The\nbest-fitting absorption column is  4.4 (+1.3, -1.2) x 10^20 cm^-2, in\nexcess of the Galactic value of 1.9 x 10^20 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 1.82 (+/-0.14) and a\nbest-fitting absorption column of 5.7 (+3.6, -3.2) x 10^20 cm^-2. The\ncounts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum  is 3.6 x 10^-11 (4.1 x 10^-11) erg cm^-2\ncount^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     5.7 (+3.6, -3.2) x 10^20 cm^-2\nGalactic foreground: 1.9 x 10^20 cm^-2\nExcess significance: 2.0 sigma\nPhoton index:\t     1.82 (+/-0.14)\n\nIf the light curve continues to decay with a power-law decay index of\n1.51, the count rate at T+24 hours will be 2.3 x 10^-3 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.4 x\n10^-14 (9.4 x 10^-14) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis are available at\nhttps://www.swift.ac.uk/xrt_products/01429020.\n\nThis circular is an official product of the Swift-XRT team.\n",
  "subject": "GRB 251230A: Swift-XRT refined Analysis",
  "eventId": "GRB 251230A",
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "submittedHow": "email",
  "bibcode": "2025GCN.43275....1S",
  "createdOn": 1767145694873
}