{
  "bibcode": "2021GCN.29260....1K",
  "body": "J.A. Kennea (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U.\nLeicester), P.A. Evans (U. Leicester), P. D'Avanzo (INAF-OAB), M.G.\nBernardini (INAF-OAB), E. Ambrosi  (INAF-IASFPA) , A. Tohuvavohu (U.\nToronto), B. Sbarufatti (PSU) and E. Troja report on behalf of the\nSwift-XRT team:\n\nWe have analysed 5.9 ks of XRT data for GRB 210104A (Troja et al. GCN\nCirc. 29233), from 69 s to 76.7 ks after the  BAT trigger. The data\ncomprise 1.8 ks in Windowed Timing (WT) mode with the remainder in\nPhoton Counting (PC) mode. The enhanced XRT position for this burst was\ngiven by Beardmore et al. (GCN Circ. 29245).\n\nThe late-time light curve (from T0+6.1 ks) can be modelled with a\npower-law decay with a decay index of alpha=1.35 (+0.08, -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 2.012 (+/-0.028). The\nbest-fitting absorption column is  1.10 (+/-0.08) x 10^21 cm^-2, in\nexcess of the Galactic value of 5.1 x 10^20 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 1.92 (+0.11, -0.10)\nand a best-fitting absorption column of 1.24 (+0.31, -0.29) x 10^21\ncm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion\nfactor deduced from this spectrum  is 3.5 x 10^-11 (3.9 x 10^-11) erg\ncm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     1.24 (+0.31, -0.29) x 10^21 cm^-2\nGalactic foreground: 5.1 x 10^20 cm^-2\nExcess significance: 4.1 sigma\nPhoton index:\t     1.92 (+0.11, -0.10)\n\nIf the light curve continues to decay with a power-law decay index of\n1.35, the count rate at T+24 hours will be 0.047 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.7 x\n10^-12 (1.8 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/01015873.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 29260,
  "createdOn": 1609856810000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 210104A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 210104A"
}