{
  "bibcode": "2024GCN.37294....1G",
  "circularId": 37294,
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "body": "J. D. Gropp (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.\nLeicester), A.P. Beardmore (U. Leicester), M. Perri (SSDC & INAF-OAR),\nV. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB), S. Dichiara\n(PSU), J.A. Kennea (PSU) and P.A. Evans report on behalf of the\nSwift-XRT team:\n\nWe have analysed 8.6 ks of XRT data for GRB 240825A, from 71 s to 56.6\nks after the  BAT trigger. The data comprise 1.2 ks in Windowed Timing\n(WT) mode (the first 10 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\ninitial decay index is alpha=3.13 (+0.24, -0.21). At T+119 s  the decay\nflattens to an alpha of 0.83 (+/-0.06). The light curve breaks again at\nT+406 s to a decay with alpha=1.121 (+0.019, -0.028),  and  again at\nT+1288 s s to alpha=1.52 (+6.48, -0.05),  before a final break at\nT+6251 s s after which the decay index is 1.25 (+0.06, -0.08).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.661 (+/-0.017). The\nbest-fitting absorption column is  1.09 (+/-0.04) x 10^22 cm^-2, at a\nredshift of 0.659, in addition to the Galactic value of 5.3 x 10^20\ncm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index\nof 1.76 (+/-0.09) and a best-fitting absorption column of 9.1 (+1.6,\n-1.4) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV\nflux conversion factor deduced from this spectrum  is 4.4 x 10^-11 (5.9\nx 10^-11) erg cm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nGalactic foreground: 5.3 x 10^20 cm^-2\nIntrinsic column:    9.1 (+1.6, -1.4) x 10^21 cm^-2 at z=0.659\nPhoton index:\t     1.76 (+/-0.09)\n\nIf the light curve continues to decay with a power-law decay index of\n1.25, the count rate at T+24 hours will be 0.093 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.1 x\n10^-12 (5.5 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/01250617.\n\nThis circular is an official product of the Swift-XRT team.\n",
  "subject": "GRB 240825A: Swift-XRT refined Analysis",
  "submittedHow": "email",
  "createdOn": 1724668996173,
  "eventId": "GRB 240825A"
}