{
  "bibcode": "2016GCN.20025....1M",
  "body": "L.M. McCauley (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester),\nK.L. Page (U. Leicester), B. Mingo (U. Leicester), A. Melandri\n(INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), B. Sbarufatti\n(INAF-OAB/PSU) and P.A. Evans (U. Leicester) report on behalf of the\nSwift-XRT team:\n\nSwift-XRT has performed follow-up observations of the INTEGRAL-detected\nburst GRB 161010A (Mereghetti et al. GCN Circ. 20021), collecting 5.0\nks of Photon Counting (PC) mode data between T0+12.0 ks and T0+30.3 ks.\n\n\nAn uncatalogued X-ray source is detected consistent with being within\n148 arcsec of the INTEGRAL position and is above the RASS limit and\nfading with 3-sigma significance, and is therefore likely the GRB\nafterglow. Using 123 s of PC mode data and 1 UVOT image, we find an\nenhanced XRT position (using the XRT-UVOT alignment and matching UVOT\nfield sources to the USNO-B1 catalogue): RA, Dec = 275.21435, -28.78515\nwhich is equivalent to:\n\nRA (J2000): 18h 20m 51.44s\nDec(J2000): -28d 47' 06.6\"\n\nwith an uncertainty of 2.9 arcsec (radius, 90% confidence). This\nposition is 12 arcsec from the INTEGRAL position. \n\nThe light curve can be modelled with a power-law decay with a decay\nindex of alpha=1.36 (+0.22, -0.21).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 1.78 (+0.18, -0.17). The\nbest-fitting absorption column is  3.1 (+0.9, -0.6) x 10^21 cm^-2,\nconsistent with the Galactic value of 2.5 x 10^21 cm^-2 (Willingale et\nal. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux\nconversion factor deduced from this spectrum  is 4.2 x 10^-11 (5.7 x\n10^-11) erg cm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     3.1 (+0.9, -0.6) x 10^21 cm^-2\nGalactic foreground: 2.5 x 10^21 cm^-2\nExcess significance: <1.6 sigma\nPhoton index:\t     1.78 (+0.18, -0.17)\n\nIf the light curve continues to decay with a power-law decay index of\n1.36, the count rate at T+24 hours will be 0.023 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 9.9 x\n10^-13 (1.3 x 10^-12) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis of the likely afterglow\nare at http://www.swift.ac.uk/ToO_GRBs/00020702/index_18.php.\nThe results of the full analysis of the XRT observations are available\nat http://www.swift.ac.uk/ToO_GRBs/00020702.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 20025,
  "createdOn": 1476171115000,
  "email": "antonino.dai@ifc.inaf.it",
  "subject": "GRB 161010A: Swift-XRT afterglow detection",
  "submitter": "Antonino D'Ai at IASF-PA  <antonino.dai@ifc.inaf.it>",
  "eventId": "GRB 161010A"
}