{
  "bibcode": "2018GCN.22756....1O",
  "body": "J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore\n(U. Leicester), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), P.\nD'Avanzo (INAF-OAB), S. J. LaPorte (PSU), J.A. Kennea (PSU), B.\nSbarufatti (INAF-OAB/PSU) and S.B. Cenko report on behalf of the\nSwift-XRT team:\n\nWe have analysed 8.4 ks of XRT data for GRB 180602A (Cenko et al. GCN\nCirc. 22752), from 130 s to 59.7 ks after the  BAT trigger. The data\ncomprise 85 s in Windowed Timing (WT) mode with the remainder in Photon\nCounting (PC) mode. The enhanced XRT position for this burst was given\nby Osborne et al. (GCN Circ. 22753).\n\nThe late-time light curve (from T0+5.6 ks) can be modelled with a\npower-law decay with a decay index of alpha=1.38 (+0.16, -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 2.36 (+0.28, -0.25). The\nbest-fitting absorption column is  4.0 (+1.3, -1.1) x 10^21 cm^-2, in\nexcess of the Galactic value of 1.6 x 10^20 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 2.04 (+0.16, -0.15)\nand a best-fitting absorption column of 4.2 (+0.8, -0.7) x 10^21 cm^-2.\nThe counts 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 (+0.8, -0.7) x 10^21 cm^-2\nGalactic foreground: 1.6 x 10^20 cm^-2\nExcess significance: 9.1 sigma\nPhoton index:\t     2.04 (+0.16, -0.15)\n\nIf the light curve continues to decay with a power-law decay index of\n1.38, the count rate at T+24 hours will be 7.3 x 10^-3 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.8 x\n10^-13 (4.5 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/00835200.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 22756,
  "createdOn": 1527994347000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 180602A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 180602A"
}