{
  "body": "J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore\n(U. Leicester), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), A.\nMelandri (INAF-OAR), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto),\nD.N. Burrows (PSU) and P.A. Evans report on behalf of the Swift-XRT\nteam:\n\nWe have analysed 1.7 ks of XRT data for GRB 240805A, from 89 s to 5.1\nks after the  BAT trigger. The data comprise 75 s in Windowed Timing\n(WT) mode (the first 6 s were taken while Swift was slewing) with the\nremainder in Photon Counting (PC) mode. Using 1639 s of PC mode data\nand 4 UVOT images, we find an enhanced XRT position (using the XRT-UVOT\nalignment and matching UVOT field sources to the USNO-B1 catalogue):\nRA, Dec = 190.91475, -53.59526 which is equivalent to:\n\nRA (J2000): 12h 43m 39.54s\nDec(J2000): -53d 35' 42.9\"\n\nwith an uncertainty of 2.1 arcsec (radius, 90% confidence).\n\nThe light curve can be modelled with an initial power-law decay with an\nindex of alpha=7.82 (+0.18, -2.12), followed by a break at T+97.3 s to\nan alpha of 1.292 (+0.027, -0.026).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.79 (+/-0.08). The\nbest-fitting absorption column is  5.1 (+/-0.5) x 10^21 cm^-2, in\nexcess of the Galactic value of 2.3 x 10^21 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 1.52 (+0.23, -0.22)\nand a best-fitting absorption column of 3.8 (+1.5, -1.2) x 10^21 cm^-2.\nThe counts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum  is 5.3 x 10^-11 (6.6 x 10^-11) erg cm^-2\ncount^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     3.8 (+1.5, -1.2) x 10^21 cm^-2\nGalactic foreground: 2.3 x 10^21 cm^-2\nExcess significance: 2.0 sigma\nPhoton index:\t     1.52 (+0.23, -0.22)\n\nIf the light curve continues to decay with a power-law decay index of\n1.292, the count rate at T+24 hours will be 0.020 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x\n10^-12 (1.4 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/01246907.\n\nThis circular is an official product of the Swift-XRT team.\n",
  "eventId": "GRB 240805A",
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "subject": "GRB 240805A: Swift-XRT refined Analysis",
  "createdOn": 1722874513812,
  "circularId": 37045,
  "bibcode": "2024GCN.37045....1O",
  "submittedHow": "email"
}