{
  "bibcode": "2021GCN.30515....1E",
  "body": "P.A. Evans (U. Leicester), M. Capalbi (INAF-IASFPA), M. Perri (SSDC &\nINAF-OAR), V. D'Elia (SSDC & INAF-OAR), A. Tohuvavohu (U. Toronto), B.\nSbarufatti (PSU), D.N. Burrows (PSU), J.P. Osborne (U. Leicester), K.L.\nPage (U. Leicester) and P. D'Avanzo report on behalf of the Swift-XRT\nteam:\n\nWe have analysed 2.5 ks of XRT data for GRB 210724A (D'Avanzo et al.\nGCN Circ. 30497), from 123 s to 84.6 ks after the  BAT trigger. The\ndata comprise 263 s in Windowed Timing (WT) mode with the remainder in\nPhoton Counting (PC) mode. Using 331 s of PC mode data and 1 UVOT\nimage, we find an enhanced XRT position (using the XRT-UVOT alignment\nand matching UVOT field sources to the USNO-B1 catalogue): RA, Dec =\n227.41131, -6.29009 which is equivalent to:\n\nRA (J2000): 15h 09m 38.72s\nDec(J2000): -06d 17' 24.3\"\n\nwith an uncertainty of 2.0 arcsec (radius, 90% confidence).\n\nThe light curve can be modelled with a power-law decay with a decay\nindex of alpha=1.17 (+0.10, -0.09).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 2.48 (+/-0.08). The\nbest-fitting absorption column is  2.08 (+0.23, -0.22) x 10^21 cm^-2,\nin excess of the Galactic value of 8.2 x 10^20 cm^-2 (Willingale et al.\n2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion\nfactor deduced from this spectrum  is 2.8 x 10^-11 (4.9 x 10^-11) erg\ncm^-2 count^-1. \n\nA summary of the WT-mode spectrum is thus:\nTotal column:\t     2.08 (+0.23, -0.22) x 10^21 cm^-2\nGalactic foreground: 8.2 x 10^20 cm^-2\nExcess significance: 9.5 sigma\nPhoton index:\t     2.48 (+/-0.08)\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/01061482.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 30515,
  "createdOn": 1627249409000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 210724A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 210724A"
}