{
  "eventId": "GRB 240118A",
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "bibcode": "2024GCN.35587....1B",
  "body": "A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi \n(INAF-IASFPA) , M. Capalbi (INAF-IASFPA), A. Tohuvavohu (U. Toronto),\nD.N. Burrows (PSU), J. D. Gropp (PSU), J.P. Osborne (U. Leicester) and\nP.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:\n\nSwift-XRT has performed follow-up observations of the\nFermi/LAT-detected burst GRB 240118A, collecting 4.7 ks of Photon\nCounting (PC) mode data between T0+96.2 ks and T0+109.0 ks. \n\nTwo uncatalogued X-ray sources are detected consistent with being\nwithin 296 arcsec of the Fermi/LAT position, of which one (\"Source 3\")\nis believed to be the afterglow. Using 4697 s of PC mode data and 3\nUVOT images, we find an enhanced XRT position (using the XRT-UVOT\nalignment and matching UVOT field sources to the USNO-B1 catalogue):\nRA, Dec = 18.53587, +29.79798 which is equivalent to:\n\nRA (J2000): 01h 14m 08.61s\nDec(J2000): +29d 47' 52.7\"\n\nwith an uncertainty of 2.7 arcsec (radius, 90% confidence). This\nposition is 2.1 arcmin from the Fermi/LAT position.  The light curve is\nconsistent with a constant source of mean count rate 3.6e-02 ct/sec. A\npower-law fit gives an index of 1.9 (+1.0, -2.8).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 2.2 (+/-0.6). The\nbest-fitting absorption column is  1.1 (+0.8, -0.6) x 10^22 cm^-2, in\nexcess of the Galactic value of 7.1 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 4.5 x 10^-11 (9.9 x 10^-11) erg\ncm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     1.1 (+0.8, -0.6) x 10^22 cm^-2\nGalactic foreground: 7.1 x 10^20 cm^-2\nExcess significance: 3.1 sigma\nPhoton index:\t     2.2 (+/-0.6)\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00021644.\nThe results of the full analysis of the XRT observations are available\nat https://www.swift.ac.uk/ToO_GRBs/00021644.\n\nThis circular is an official product of the Swift-XRT team.\n\n",
  "createdOn": 1705790491803,
  "circularId": 35587,
  "subject": "GRB 240118A: Swift-XRT afterglow detection",
  "submittedHow": "email"
}