{
  "body": "D.N. Burrows (PSU), M. A. Williams (PSU), J.P. Osborne (U. Leicester),\nK.L. Page (U. Leicester), A. D'Ai (INAF-IASFPA), A. Melandri\n(INAF-OAR), T. Sbarrato (INAF-OAB), S. Dichiara (PSU) and P.A. Evans\nreport on behalf of the Swift-XRT team:\n\nWe have analysed 8.3 ks of XRT data for GRB 250312A, from 385 s to 34.7\nks after the  BAT trigger. The data are entirely in Photon Counting\n(PC) mode. \n\nThe light curve can be modelled with a power-law decay with a decay\nindex of alpha=0.51 (+/-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 1.80 (+0.22, -0.21). The\nbest-fitting absorption column is  1.3 (+0.7, -0.6) x 10^21 cm^-2, in\nexcess of the Galactic value of 1.8 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 3.9 x 10^-11 (4.7 x 10^-11) erg\ncm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     1.3 (+0.7, -0.6) x 10^21 cm^-2\nGalactic foreground: 1.8 x 10^20 cm^-2\nExcess significance: 3.0 sigma\nPhoton index:\t     1.80 (+0.22, -0.21)\n\nIf the light curve continues to decay with a power-law decay index of\n0.51, the count rate at T+24 hours will be 0.022 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.5 x\n10^-13 (1.0 x 10^-12) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/01294765.\n\nThis circular is an official product of the Swift-XRT team.\n",
  "eventId": "GRB 250312A",
  "bibcode": "2025GCN.39697....1B",
  "circularId": 39697,
  "createdOn": 1741828863377,
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "submittedHow": "email",
  "subject": "GRB 250312A: Swift-XRT refined Analysis"
}