{
  "bibcode": "2018GCN.22707....1D",
  "body": "A. D'Ai (INAF-IASFPA), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU),\nD.N. Burrows (PSU), A.P. Beardmore (U. Leicester), P.A. Evans (U.\nLeicester), S.L. Gibson (U. Leicester), A. Melandri (INAF-OAB), P.\nD'Avanzo (INAF-OAB) and J.D. Gropp report on behalf of the Swift-XRT\nteam:\n\nWe have analysed 4.9 ks of XRT data for GRB 180510A (Gropp et al. GCN\nCirc. 22695), from 77 s to 40.5 ks after the  BAT trigger. The data\ncomprise 228 s in Windowed Timing (WT) mode (the first 9 s were taken\nwhile Swift was slewing) with the remainder in Photon Counting (PC)\nmode. The refined XRT position is RA, Dec = 276.3314, -31.9081 which is\nequivalent to:\n\nRA (J2000): 18 25 19.54\nDec(J2000): -31 54 29.1\n\nwith an uncertainty of 3.6 arcsec (radius, 90% confidence).\n\nThe late-time light curve (from T0+15.8 ks) can be modelled with a\npower-law decay with a decay index of alpha=1.2 (+/-0.4).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.94 (+0.08, -0.07). The\nbest-fitting absorption column is  5.2 (+/-0.5) x 10^21 cm^-2, in\nexcess of the Galactic value of 2.1 x 10^21 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 2.01 (+0.30, -0.28)\nand a best-fitting absorption column of 3.5 (+1.4, -1.2) 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 (5.8 x 10^-11) erg cm^-2\ncount^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     3.5 (+1.4, -1.2) x 10^21 cm^-2\nGalactic foreground: 2.1 x 10^21 cm^-2\nExcess significance: 1.9 sigma\nPhoton index:\t     2.01 (+0.30, -0.28)\n\nIf the light curve continues to decay with a power-law decay index of\n1.2, the count rate at T+24 hours will be 0.016 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.2 x\n10^-13 (9.4 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/00831810.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 22707,
  "createdOn": 1526068024000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 180510A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 180510A"
}