{
  "eventId": "GRB 251221A",
  "submittedHow": "email",
  "body": "K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), S. Campana\n(INAF-OAB), A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB), S. Dichiara\n(PSU), J.A. Kennea (PSU), D.N. Burrows (PSU) and P.A. Evans report on\nbehalf of the Swift-XRT team:\n\nWe have analysed 4.3 ks of XRT data for GRB 251221A, from 122 s to 56.3\nks after the   trigger. The data comprise 8 s in Windowed Timing (WT)\nmode (taken while Swift was slewing), with the remainder in Photon\nCounting (PC) mode. \n\nThe light curve can be modelled with a power-law decay with a decay\nindex of alpha=1.13 (+0.17, -0.14).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 1.49 (+0.19, -0.18). The\nbest-fitting absorption column is  1.11 (+0.24, -0.22) x 10^22 cm^-2,\nin excess of the Galactic value of 7.3 x 10^21 cm^-2 (Willingale et al.\n2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion\nfactor deduced from this spectrum  is 6.8 x 10^-11 (9.5 x 10^-11) erg\ncm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     1.11 (+0.24, -0.22) x 10^22 cm^-2\nGalactic foreground: 7.3 x 10^21 cm^-2\nExcess significance: 2.8 sigma\nPhoton index:\t     1.49 (+0.19, -0.18)\n\nIf the light curve continues to decay with a power-law decay index of\n1.13, the count rate at T+24 hours will be 1.9 x 10^-3 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.3 x\n10^-13 (1.8 x 10^-13) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis are available at\nhttps://www.swift.ac.uk/xrt_products/01426088.\n\nThis circular is an official product of the Swift-XRT team.\n",
  "bibcode": "2025GCN.43179....1P",
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "circularId": 43179,
  "subject": "GRB 251221A: Swift-XRT refined Analysis",
  "createdOn": 1766381892762
}