{
  "createdOn": 1747751394517,
  "bibcode": "2025GCN.40503....1P",
  "body": "M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), M.A. Williams\n(PSU), S. Dichiara (PSU), J.A. Kennea (PSU), J.P. Osborne (U.\nLeicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), B.\nSbarufatti (INAF-OAB) and P.A. Evans report on behalf of the Swift-XRT\nteam:\n\nWe have analysed 6.7 ks of XRT data for GRB 250520A, from 127 s to 34.5\nks after the   trigger. The data comprise 16 s in Windowed Timing (WT)\nmode (the first 9 s were taken while Swift was slewing) with the\nremainder in Photon Counting (PC) mode. \n\nThe light curve can be modelled with a power-law decay with a decay\nindex of alpha=2.35 (+0.23, -0.22).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 2.1 (+/-0.4). The\nbest-fitting absorption column is  1.3 (+0.5, -0.4) x 10^22 cm^-2, in\nexcess of the Galactic value of 3.7 x 10^21 cm^-2 (Willingale et al.\n2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion\nfactor deduced from this spectrum  is 5.0 x 10^-11 (1.1 x 10^-10) erg\ncm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     1.3 (+0.5, -0.4) x 10^22 cm^-2\nGalactic foreground: 3.7 x 10^21 cm^-2\nExcess significance: 3.6 sigma\nPhoton index:\t     2.1 (+/-0.4)\n\nIf the light curve continues to decay with a power-law decay index of\n2.35, the count rate at T+24 hours will be 10.0 x 10^-7 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.0 x\n10^-17 (1.1 x 10^-16) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/01315630.\n\nThis circular is an official product of the Swift-XRT team.\n",
  "circularId": 40503,
  "submittedHow": "email",
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "eventId": "GRB 250520A",
  "subject": "GRB 250520A: Swift-XRT refined Analysis"
}