{
  "submittedHow": "email",
  "createdOn": 1740182957119,
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "body": "C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), M. A. Williams (PSU), S.\nDichiara (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L.\nPage (U. Leicester), A.P. Beardmore (U. Leicester), R. Brivio\n(INAF-OAB) and P.A. Evans report on behalf of the Swift-XRT team:\n\nWe have analysed 7.0 ks of XRT data for GRB 250221A, from 107 s to 66.9\nks after the  BAT trigger. The data comprise 9 s in Windowed Timing\n(WT) mode (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=1.06 (+/-0.06).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 2.09 (+0.24, -0.23). The\nbest-fitting absorption column is  1.4 (+0.7, -0.6) x 10^21 cm^-2, in\nexcess of the Galactic value of 3.7 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 3.3 x 10^-11 (4.4 x 10^-11) erg\ncm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     1.4 (+0.7, -0.6) x 10^21 cm^-2\nGalactic foreground: 3.7 x 10^20 cm^-2\nExcess significance: 2.7 sigma\nPhoton index:\t     2.09 (+0.24, -0.23)\n\nIf the light curve continues to decay with a power-law decay index of\n1.06, the count rate at T+24 hours will be 2.5 x 10^-3 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.4 x\n10^-14 (1.1 x 10^-13) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/01290305.\n\nThis circular is an official product of the Swift-XRT team.\n",
  "bibcode": "2025GCN.39414....1S",
  "subject": "GRB 250221A: Swift-XRT refined Analysis",
  "circularId": 39414,
  "eventId": "GRB 250221A"
}