{
  "bibcode": "2017GCN.21989....1D",
  "body": "A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), B. Sbarufatti\n(INAF-OAB/PSU), D.N. Burrows (PSU), A. Tohuvavohu (PSU), S.L. Gibson\n(U. Leicester), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester),\nP. D'Avanzo (INAF-OAB) and P.A. Evans (U. Leicester) report on behalf\nof the Swift-XRT team:\n\nSwift-XRT has performed follow-up observations of the\nFermi/LAT-detected burst GRB 171010A (Omodei et al. GCN Circ. 21985),\ncollecting 5.0 ks of Photon Counting (PC) mode data between T0+24.2 ks\nand T0+41.7 ks. \n\nFour uncatalogued X-ray sources are detected, of which one (\"Source 2\")\nis above the RASS limit, and is therefore likely the GRB afterglow.\nUsing 4537 s of PC mode data and 7 UVOT images, we find an enhanced XRT\nposition (using the XRT-UVOT alignment and matching UVOT field sources\nto the USNO-B1 catalogue): RA, Dec = 66.58092, -10.46325 which is\nequivalent to:\n\nRA (J2000): 04h 26m 19.42s\nDec(J2000): -10d 27' 47.7\"\n\nwith an uncertainty of 1.4 arcsec (radius, 90% confidence). This\nposition is 10.5 arcmin from the Fermi/LAT position. \n\nThe light curve can be modelled with a power-law decay with a decay\nindex of alpha=2.2 (+/-0.3).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 2.01 (+/-0.15). The\nbest-fitting absorption column is  3.6 (+0.7, -0.6) x 10^21 cm^-2, in\nexcess of the Galactic value of 7.0 x 10^20 cm^-2 (Willingale et al.\n2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion\nfactor deduced from this spectrum  is 3.3 x 10^-11 (5.0 x 10^-11) erg\ncm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     3.6 (+0.7, -0.6) x 10^21 cm^-2\nGalactic foreground: 7.0 x 10^20 cm^-2\nExcess significance: 7.4 sigma\nPhoton index:\t     2.01 (+/-0.15)\n\nIf the light curve continues to decay with a power-law decay index of\n2.2, the count rate at T+24 hours will be 0.054 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.8 x\n10^-12 (2.7 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/00020778.\nThe results of the full analysis of the XRT observations are available\nat http://www.swift.ac.uk/ToO_GRBs/00020778.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 21989,
  "createdOn": 1507729724000,
  "email": "klp5@leicester.ac.uk",
  "subject": "GRB 171010A: Swift-XRT afterglow detection",
  "submitter": "Kim Page at U.of Leicester  <klp5@leicester.ac.uk>",
  "eventId": "GRB 171010A"
}