{
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "circularId": 34489,
  "body": "S. Dichiara (PSU), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), A.P.\nBeardmore (U. Leicester), J.P. Osborne (U. Leicester), E. Ambrosi \n(INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR)\nand P.A. Evans report on behalf of the Swift-XRT team:\n\nWe have analysed 6.4 ks of XRT data for GRB 230818A, from 125 s to 40.1\nks after the  BAT trigger. The data comprise 41 s in Windowed Timing\n(WT) mode (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 an initial power-law decay with an\nindex of alpha=2.2 (+0.5, -0.4), followed by a break at T+385 s to an\nalpha of 0.76 (+/-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 1.96 (+0.21, -0.20). The\nbest-fitting absorption column is  1.8 (+/-0.7) x 10^21 cm^-2, in\nexcess of the Galactic value of 1.1 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 3.6 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     1.8 (+/-0.7) x 10^21 cm^-2\nGalactic foreground: 1.1 x 10^21 cm^-2\nExcess significance: 1.8 sigma\nPhoton index:\t     1.96 (+0.21, -0.20)\n\nIf the light curve continues to decay with a power-law decay index of\n0.76, the count rate at T+24 hours will be 0.012 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.3 x\n10^-13 (5.7 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/01186032.\n\nThis circular is an official product of the Swift-XRT team.\n",
  "eventId": "GRB 230818A",
  "bibcode": "2023GCN.34489....1D",
  "submittedHow": "email",
  "createdOn": 1692458395878,
  "subject": "GRB 230818A: Swift-XRT refined Analysis"
}