{
  "bibcode": "2020GCN.28740....1S",
  "body": "B. Sbarufatti (PSU), D.N. Burrows (PSU), J.P. Osborne (U. Leicester),\nK.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), T. Sbarrato\n(INAF-OAB), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), J. D.\nGropp (PSU) and P.A. Evans (U. Leicester) report on behalf of the\nSwift-XRT team:\n\nSwift-XRT has performed follow-up observations of the\nFermi/LAT-detected burst GRB 201020B (Arimoto et al. GCN Circ. 28716),\ncollecting 1.7 ks of Photon Counting (PC) mode data between T0+72.1 ks\nand T0+74.3 ks. \n\nAn uncatalogued X-ray source is detected and is above the RASS limit,\nand is therefore likely the GRB afterglow. Using 1015 s of PC mode data\nand 2 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 = 75.46680, +77.06830 which is equivalent to:\n\nRA (J2000): 05h 01m 52.03s\nDec(J2000): +77d 04' 05.9\"\n\nwith an uncertainty of 2.0 arcsec (radius, 90% confidence). This\nposition is 9.6 arcmin from the Fermi/LAT position and consistent with\nthe optical counterpart detected by MASTER (Lipunov et al. GCN Circ.\n28718).  The light curve is consistent with a constant source of mean\ncount rate 1.5e-01 ct/sec. With the currently available dataset we\ncannot constrain the temporal evolution.\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 2.2 (+0.4, -0.3). The\nbest-fitting absorption column is  4.0 (+1.7, -1.4) x 10^21 cm^-2, in\nexcess of the Galactic value of 1.4 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 3.3 x 10^-11 (5.7 x 10^-11) erg\ncm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     4.0 (+1.7, -1.4) x 10^21 cm^-2\nGalactic foreground: 1.4 x 10^21 cm^-2\nExcess significance: 3.0 sigma\nPhoton index:\t     2.2 (+0.4, -0.3)\n\nThe results of the XRT-team automatic analysis of the likely afterglow\nare at https://www.swift.ac.uk/ToO_GRBs/00021035/Source1.php.\nThe results of the full analysis of the XRT observations are available\nat https://www.swift.ac.uk/ToO_GRBs/00021035.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 28740,
  "createdOn": 1603357479000,
  "email": "paolo.davanzo@inaf.it",
  "subject": "GRB 201020B: Swift-XRT afterglow detection",
  "submitter": "Paolo D'Avanzo at INAF - OAB  <paolo.davanzo@inaf.it>",
  "eventId": "GRB 201020B"
}