{
  "bibcode": "2021GCN.29876....1O",
  "body": "J.P. Osborne (U. Leicester), M. Capalbi (INAF-IASFPA), M. Perri (SSDC &\nINAF-OAR), V. D'Elia (SSDC & INAF-OAR), J. D. Gropp (PSU), J.A. Kennea\n(PSU), A. Tohuvavohu (U. Toronto), K.L. Page (U. Leicester), A.P.\nBeardmore (U. Leicester) and M.J. Moss report on behalf of the\nSwift-XRT team:\n\nWe have analysed 4.8 ks of XRT data for GRB 210420B (Moss et al. GCN\nCirc. 29844), from 141 s to 87.5 ks after the  BAT trigger. The data\ncomprise 177 s in Windowed Timing (WT) mode with the remainder in\nPhoton Counting (PC) mode. The refined XRT position is RA, Dec =\n254.3227, +42.5696 which is equivalent to:\n\nRA (J2000): 16 57 17.45\nDec(J2000): +42 34 10.6\n\nwith an uncertainty of 3.5 arcsec (radius, 90% confidence).\n\nThe light curve can be modelled with an initial power-law decay with an\nindex of alpha=2.23 (+0.11, -0.12), followed by a break at T+425 s to\nan alpha of 1.13 (+/-0.07).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.72 (+0.08, -0.07). The\nbest-fitting absorption column is  9 (+11, -9) x 10^20 cm^-2, at a\nredshift of 1.4, in addition to the Galactic value of 2.1 x 10^20 cm^-2\n(Willingale et al. 2013). The PC mode spectrum has a photon index of\n1.61 (+0.08, -0.07) and a best-fitting absorption column consistent\nwith the Galactic value. The counts to observed (unabsorbed) 0.3-10 keV\nflux conversion factor deduced from this spectrum  is 4.0 x 10^-11 (4.2\nx 10^-11) erg cm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nGalactic foreground: 2.1 x 10^20 cm^-2\nIntrinsic column:    2.1 (+6.0, -0.0) x 10^20 cm^-2 at z=1.4\nPhoton index:\t     1.61 (+0.08, -0.07)\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/01044382.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 29876,
  "createdOn": 1619045046000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 210420B: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 210420B"
}