{
  "subject": "GRB 250823A: Swift-XRT refined Analysis",
  "body": "S. Dichiara (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U.\nLeicester), S. Campana (INAF-OAB), A. Melandri (INAF-OAR), T. Sbarrato\n(INAF-OAB), J.A. Kennea (PSU), D.N. Burrows (PSU) and P.A. Evans report\non behalf of the Swift-XRT team:\n\nWe have analysed 4.8 ks of XRT data for GRB 250823A, from 111 s to 44.7\nks after the   trigger. The data comprise 313 s in Windowed Timing (WT)\nmode (the first 7 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\nlight curve initially rises, with an index alpha=-1.5 (+0.0, -0.6). At\nT+120 s it breaks to an alpha of 3.33 (+/-0.09). The light curve breaks\nagain at T+349 s to a decay with alpha=2.31 (+0.23, -0.21),  before a\nfinal break at T+1667 s s after which the decay index is 0.78 (+0.13,\n-0.12).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.91 (+/-0.04). The\nbest-fitting absorption column is  1.99 (+0.16, -0.15) x 10^21 cm^-2,\nin excess of the Galactic value of 1.1 x 10^21 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 1.92 (+0.28, -0.26)\nand a best-fitting absorption column of 1.9 (+1.0, -0.8) x 10^21 cm^-2.\nThe counts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum  is 3.8 x 10^-11 (5.0 x 10^-11) erg cm^-2\ncount^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     1.9 (+1.0, -0.8) x 10^21 cm^-2\nGalactic foreground: 1.1 x 10^21 cm^-2\nExcess significance: <1.6 sigma\nPhoton index:\t     1.92 (+0.28, -0.26)\n\nIf the light curve continues to decay with a power-law decay index of\n0.78, the count rate at T+24 hours will be 9.6 x 10^-3 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.6 x\n10^-13 (4.8 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/01344586.\n\nThis circular is an official product of the Swift-XRT team.\n",
  "bibcode": "2025GCN.41531....1D",
  "circularId": 41531,
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "createdOn": 1756067465720,
  "eventId": "GRB 250823A",
  "submittedHow": "email"
}