{
  "bibcode": "2018GCN.22817....1M",
  "body": "A. Melandri (INAF-OAB), S. J. LaPorte (PSU), J.A. Kennea (PSU), B.\nSbarufatti (INAF-OAB/PSU), Z. Liu (NAOC / U. Leicester), J.P. Osborne\n(U. Leicester), K.L. Page (U. Leicester), P. D'Avanzo (INAF-OAB), V.\nD'Elia (ASDC) and P.A. Evans report on behalf of the Swift-XRT team:\n\nWe have analysed 6.6 ks of XRT data for GRB 180620B (Evans et al. GCN\nCirc. 22807), from 89 s to 56.0 ks after the  BAT trigger. The data\ncomprise 237 s 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. 22814).\n\nThe late-time light curve (from T0+4.3 ks) can be modelled with a\npower-law decay with a decay index of alpha=0.61 (+/-0.08).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 2.34 (+/-0.05). The\nbest-fitting absorption column is  2.30 (+/-0.15) x 10^21 cm^-2, in\nexcess of the Galactic value of 1.4 x 10^20 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 1.99 (+0.11, -0.10)\nand a best-fitting absorption column of 1.6 (+/-0.3) x 10^21 cm^-2. The\ncounts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum  is 3.5 x 10^-11 (4.6 x 10^-11) erg cm^-2\ncount^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     1.6 (+/-0.3) x 10^21 cm^-2\nGalactic foreground: 1.4 x 10^20 cm^-2\nExcess significance: 7.9 sigma\nPhoton index:\t     1.99 (+0.11, -0.10)\n\nIf the light curve continues to decay with a power-law decay index of\n0.61, the count rate at T+24 hours will be 0.12 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.1 x\n10^-12 (5.5 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/00843211.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 22817,
  "createdOn": 1529575452000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 180620B: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 180620B"
}