{
  "bibcode": "2018GCN.22511....1G",
  "body": "S.L. Gibson (U. Leicester), J.P. Osborne (U. Leicester), K.L. Page (U.\nLeicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. D'Ai\n(INAF-IASFPA), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), A.\nTohuvavohu (PSU) and A. Melandri report on behalf of the Swift-XRT\nteam:\n\nWe have analysed 6.1 ks of XRT data for GRB 180316A (Melandri et al.\nGCN Circ. 22500), from 101 s to 28.6 ks after the  BAT trigger. The\ndata comprise 534 s in Windowed Timing (WT) mode with the remainder in\nPhoton Counting (PC) mode. The enhanced XRT position for this burst was\ngiven by Evans et al. (GCN Circ. 22501).\n\nThe late-time light curve (from T0+4.4 ks) can be modelled with an\ninitial power-law decay with an index of alpha=-0.0 (+/-0.6), followed\nby a break at T+8729 s to an alpha of 2.1 (+/-0.3).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.94 (+0.07, -0.04). The\nbest-fitting absorption column is  2.038 (+0.286, -0.012) x 10^21\ncm^-2, consistent with the Galactic value of 2.0 x 10^21 cm^-2\n(Willingale et al. 2013). The PC mode spectrum has a photon index of\n2.05 (+/-0.16) and a best-fitting absorption column of 3.3 (+/-0.7) x\n10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux\nconversion factor deduced from this spectrum  is 3.7 x 10^-11 (5.7 x\n10^-11) erg cm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     3.3 (+/-0.7) x 10^21 cm^-2\nGalactic foreground: 2.0 x 10^21 cm^-2\nExcess significance: 3.2 sigma\nPhoton index:\t     2.05 (+/-0.16)\n\nIf the light curve continues to decay with a power-law decay index of\n2.1, the count rate at T+24 hours will be 2.9 x 10^-3 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x\n10^-13 (1.7 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/00814677.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 22511,
  "createdOn": 1521215862000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 180316A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 180316A"
}