{
  "body": "K.L. Page (U. Leicester), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA),\nS. Campana (INAF-OAB), S. Dichiara (PSU), J.A. Kennea (PSU), D.N.\nBurrows (PSU), A.P. Beardmore (U. Leicester) and P.A. Evans report on\nbehalf of the Swift-XRT team:\n\nWe have analysed 6.4 ks of XRT data for GRB 250920B, from 87 s to 22.3\nks after the   trigger. The data comprise 395 s in Windowed Timing (WT)\nmode (the first 2 s were taken while Swift was slewing) with the\nremainder in Photon Counting (PC) mode. The refined XRT position is RA,\nDec = 187.3175, +47.8376 which is equivalent to:\n\nRA (J2000): 12h 29m 16.21s\nDec(J2000): +47d 50' 15.2\"\n\nwith an uncertainty of 3.5 arcsec (radius, 90% confidence).\n\nThe late-time light curve (from T0+3.8 ks) can be modelled with a\npower-law decay with a decay index of alpha=1.20 (+/-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 1.490 (+0.035, -0.017). The\nbest-fitting absorption column is  consistent with the Galactic value\nof 1.1 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has\na photon index of 1.89 (+/-0.07) and a best-fitting absorption column\nof 3.3 (+1.5, -1.4) x 10^20 cm^-2. The counts to observed (unabsorbed)\n0.3-10 keV flux conversion factor deduced from this spectrum  is 3.5 x\n10^-11 (3.7 x 10^-11) erg cm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     3.3 (+1.5, -1.4) x 10^20 cm^-2\nGalactic foreground: 1.1 x 10^20 cm^-2\nExcess significance: 2.5 sigma\nPhoton index:\t     1.89 (+/-0.07)\n\nIf the light curve continues to decay with a power-law decay index of\n1.20, the count rate at T+24 hours will be 0.10 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.5 x\n10^-12 (3.8 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/01351008.\n\nThis circular is an official product of the Swift-XRT team.\n",
  "submittedHow": "email",
  "bibcode": "2025GCN.41909....1P",
  "eventId": "GRB 250920B",
  "createdOn": 1758387332389,
  "subject": "GRB 250920B: Swift-XRT refined Analysis",
  "circularId": 41909,
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>"
}