{
  "bibcode": "2018GCN.22876....1E",
  "body": "P.A. Evans (U. Leicester), S.L. Gibson (U. Leicester), Z. Liu (NAOC /\nU. Leicester), A. Melandri (INAF-OAB), V. D'Elia (ASDC), A. Tohuvavohu\n(PSU), S. J. LaPorte (PSU), J.A. Kennea (PSU) and P. D'Avanzo report on\nbehalf of the Swift-XRT team:\n\nWe have analysed 6.3 ks of XRT data for GRB 180630A (D'Avanzo et al.\nGCN Circ. 22872), from 87 s to 29.0 ks after the  BAT trigger. The data\ncomprise 69 s in Windowed Timing (WT) mode with the remainder in Photon\nCounting (PC) mode. The enhanced XRT position for this burst was given\nby Beardmore et al. (GCN Circ. 22873).\n\nThe light curve can be modelled with a series of power-law decays. The\ninitial decay index is alpha=3.04 (+0.61, -0.21). At T+155 s  the decay\nflattens to an alpha of 0.25 (+0.26, -0.09). The light curve breaks\nagain at T+659 s to a decay with alpha=0.80 (+0.07, -0.05),  before a\nfinal break at T+24.3 ks s after which the decay index is 4.4 (+3.6,\n-2.2).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 2.91 (+0.21, -0.17). The\nbest-fitting absorption column is  consistent with the Galactic value\nof 1.3 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has\na photon index of 1.64 (+/-0.12) and a best-fitting absorption column\nof 1.7 (+0.5, -0.3) x 10^21 cm^-2. The counts to observed (unabsorbed)\n0.3-10 keV flux conversion factor deduced from this spectrum  is 4.3 x\n10^-11 (5.1 x 10^-11) erg cm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     1.7 (+0.5, -0.3) x 10^21 cm^-2\nGalactic foreground: 1.3 x 10^21 cm^-2\nExcess significance: <1.6 sigma\nPhoton index:\t     1.64 (+/-0.12)\n\nIf the light curve continues to decay with a power-law decay index of\n4.4, the count rate at T+24 hours will be 4.3 x 10^-4 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.8 x\n10^-14 (2.2 x 10^-14) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00845443.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 22876,
  "createdOn": 1530394417000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 180630A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 180630A"
}