{
  "bibcode": "2018GCN.22598....1B",
  "body": "D.N. Burrows (PSU), A. Tohuvavohu (PSU), S. J. LaPorte (PSU), J.P.\nOsborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U.\nLeicester), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), P. D'Avanzo\n(INAF-OAB) and S.J. LaPorte report on behalf of the Swift-XRT team:\n\nWe have analysed 8.4 ks of XRT data for GRB 180404B (LaPorte et al. GCN\nCirc. 22590), from 63 s to 30.6 ks after the  BAT trigger. The data\ncomprise 349 s in Windowed Timing (WT) mode (the first 5 s were taken\nwhile Swift was slewing) with the remainder in Photon Counting (PC)\nmode. The enhanced XRT position for this burst was given by Beardmore\net al. (GCN Circ. 22594).\n\nThe late-time light curve (from T0+5.2 ks) can be modelled with a\npower-law decay with a decay index of alpha=1.52 (+0.14, -0.13).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.61 (+/-0.04). The\nbest-fitting absorption column is  3.00 (+0.25, -0.23) x 10^21 cm^-2,\nin excess of the Galactic value of 1.1 x 10^20 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 2.06 (+/-0.14) and a\nbest-fitting absorption column of 4.2 (+/-0.7) x 10^21 cm^-2. The\ncounts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum  is 3.8 x 10^-11 (6.2 x 10^-11) erg cm^-2\ncount^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     4.2 (+/-0.7) x 10^21 cm^-2\nGalactic foreground: 1.1 x 10^20 cm^-2\nExcess significance: 10.0 sigma\nPhoton index:\t     2.06 (+/-0.14)\n\nIf the light curve continues to decay with a power-law decay index of\n1.52, the count rate at T+24 hours will be 4.5 x 10^-3 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.7 x\n10^-13 (2.8 x 10^-13) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00821902.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 22598,
  "createdOn": 1522849894000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 180404B: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 180404B"
}