{
  "bibcode": "2018GCN.23125....1L",
  "body": "Z. Liu (NAOC / U. Leicester), A. Melandri (INAF-OAB), P. D'Avanzo\n(INAF-OAB), V. D'Elia (ASDC), A. Tohuvavohu (PSU), S. J. LaPorte (PSU),\nJ.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.\nLeicester) and M.J. Moss report on behalf of the Swift-XRT team:\n\nWe have analysed 3.9 ks of XRT data for GRB 180809B (Moss et al. GCN\nCirc. 23105), from 74 s to 12.6 ks after the  BAT trigger. The data\ncomprise 1.7 ks in Windowed Timing (WT) mode with the remainder in\nPhoton Counting (PC) mode. Using 1724 s of PC mode data and 4 UVOT\nimages, we find an enhanced XRT position (using the XRT-UVOT alignment\nand matching UVOT field sources to the USNO-B1 catalogue): RA, Dec =\n299.69997, -15.29893 which is equivalent to:\n\nRA (J2000): 19h 58m 47.99s\nDec(J2000): -15d 17' 56.1\"\n\nwith an uncertainty of 1.4 arcsec (radius, 90% confidence).\n\nThe late-time light curve (from T0+4.7 ks) can be modelled with a\npower-law decay with a decay index of alpha=1.37 (+/-0.12).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.609 (+/-0.017). The\nbest-fitting absorption column is  2.29 (+0.09, -0.08) x 10^21 cm^-2,\nin excess of the Galactic value of 1.2 x 10^21 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 1.63 (+/-0.11) and a\nbest-fitting absorption column of 2.4 (+/-0.5) x 10^21 cm^-2. The\ncounts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum  is 4.6 x 10^-11 (5.6 x 10^-11) erg cm^-2\ncount^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     2.4 (+/-0.5) x 10^21 cm^-2\nGalactic foreground: 1.2 x 10^21 cm^-2\nExcess significance: 4.0 sigma\nPhoton index:\t     1.63 (+/-0.11)\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00852553.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 23125,
  "createdOn": 1533933603000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 180809B: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 180809B"
}