{
  "bibcode": "2019GCN.25251....1O",
  "body": "J.P. Osborne (U. Leicester), E. Ambrosi  (INAF-IASFPA) , M. Capalbi\n(INAF-IASFPA), M. Perri (ASDC), J. D. Gropp (PSU), A. Tohuvavohu (PSU),\nJ.A. Kennea (PSU), K.L. Page (U. Leicester) and P.A. Evans (U.\nLeicester) report on behalf of the Swift-XRT team:\n\nSwift-XRT has performed follow-up observations of the\nFermi/LAT-detected burst GRB 190731A (Ohno et al. GCN Circ. 25244),\ncollecting 5.0 ks of Photon Counting (PC) mode data between T0+33.4 ks\nand T0+62.9 ks. \n\nEleven uncatalogued X-ray sources are detected, of which one (\"Source\n1\") is fading with 3-sigma significance, and is therefore likely the\nGRB afterglow. Using 1953 s of PC mode data and 4 UVOT images, we find\nan enhanced XRT position (using the XRT-UVOT alignment and matching\nUVOT field sources to the USNO-B1 catalogue): RA, Dec = 339.72015,\n-76.57744 which is equivalent to:\n\nRA (J2000): 22h 38m 52.84s\nDec(J2000): -76d 34' 38.8\"\n\nwith an uncertainty of 2.2 arcsec (radius, 90% confidence). This\nposition is 4.0 arcmin from the Fermi/LAT position. \n\nThe light curve can be modelled with a power-law decay with a decay\nindex of alpha=1.3 (+0.6, -0.7).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 2.5 (+/-0.5). The\nbest-fitting absorption column is  5.9 (+2.8, -2.2) x 10^21 cm^-2, in\nexcess of the Galactic value of 9.8 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 (7.8 x 10^-11) erg\ncm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     5.9 (+2.8, -2.2) x 10^21 cm^-2\nGalactic foreground: 9.8 x 10^20 cm^-2\nExcess significance: 3.6 sigma\nPhoton index:\t     2.5 (+/-0.5)\n\nIf the light curve continues to decay with a power-law decay index of\n1.3, the count rate at T+24 hours will be 0.015 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.9 x\n10^-13 (1.2 x 10^-12) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis of the likely afterglow\nare at https://www.swift.ac.uk/ToO_GRBs/00020914/Source1.php.\nThe results of the full analysis of the XRT observations are available\nat https://www.swift.ac.uk/ToO_GRBs/00020914.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 25251,
  "createdOn": 1564694667000,
  "email": "ab271@leicester.ac.uk",
  "subject": "GRB 190731A: Swift-XRT afterglow detection",
  "submitter": "Andy Beardmore at U Leicester  <ab271@leicester.ac.uk>",
  "eventId": "GRB 190731A"
}