{
  "bibcode": "2015GCN.17939....1P",
  "body": "K.L. Page (U. Leicester), C. Pagani (U. Leicester), P. D'Avanzo\n(INAF-OAB), V. D'Elia (ASDC), A. D'ai (INAF-IASFPA), J.A. Kennea (PSU),\nB. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), A.P. Beardmore (U.\nLeicester) and A.Y. Lien report on behalf of the Swift-XRT team:\n\nWe have analysed 10 ks of XRT data for GRB 150616A (Lien et al. GCN\nCirc. 17936), from 561 s to 31.6 ks after the  BAT trigger. The data\ncomprise 979 s in Windowed Timing (WT) mode (the first 8 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 Evans et\nal. (GCN Circ. 17937).\n\nThe late-time light curve (from T0+6.3 ks) can be modelled with an\ninitial power-law decay with an index of alpha=3.785 (+0.019, -0.768),\nfollowed by a break at T+7888 s to an alpha of 0.94 (+0.14, -0.16).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.75 (+/-0.04). The\nbest-fitting absorption column is  5.06 (+0.31, -0.30) x 10^21 cm^-2,\nin excess of the Galactic value of 3.4 x 10^20 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 2.15 (+0.10, -0.09)\nand a best-fitting absorption column of 4.6 (+/-0.5) x 10^21 cm^-2. The\ncounts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum  is 3.7 x 10^-11 (6.5 x 10^-11) erg cm^-2\ncount^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     4.6 (+/-0.5) x 10^21 cm^-2\nGalactic foreground: 3.4 x 10^20 cm^-2\nExcess significance: 15.3 sigma\nPhoton index:\t     2.15 (+0.10, -0.09)\n\nIf the light curve continues to decay with a power-law decay index of\n0.94, the count rate at T+24 hours will be 0.050 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.9 x\n10^-12 (3.3 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/00644259.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 17939,
  "createdOn": 1434539165000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 150616A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 150616A"
}