{
  "eventId": "GRB 240828A",
  "createdOn": 1724936315893,
  "body": "A.P. Beardmore (U. Leicester), B. Sbarufatti (INAF-OAB), C. Salvaggio\n(INAF-OAB), M. Ferro (INAF-OAB), J.A. Kennea (PSU), D.N. Burrows (PSU),\nM. A. Williams (PSU), J.P. Osborne (U. Leicester) and P.A. Evans (U.\nLeicester) reports on behalf of the Swift-XRT team:\n\nSwift-XRT has performed follow-up observations of the\nFermi/LAT-detected burst GRB 240828A in a series of observations tiled\non the sky. The total exposure time is 3.3 ks, distributed over 3\ntiles; the maximum exposure at a single sky location was 2.3 ks. The\ndata were collected between T0+42.1 ks and T0+60.2 ks, and are entirely\nin Photon Counting (PC) mode. \n\nSix uncatalogued X-ray sources are detected, of which one (\"Source 3\")\nis above the RASS 3-sigma upper limit at this position, and is\ntherefore likely the GRB afterglow.  The position of this source is RA,\nDec=225.5130, +36.5285 which is equivalent to:\n\nRA (J2000): 15:02:3.12\nDec(J2000): +36:31:42.5\n\nwith an uncertainty of 3.9 arcsec (radius, 90% confidence).  This\nposition is 6.8 arcmin from the Fermi/LAT position. \n\nThe light curve can be modelled with a power-law decay with a decay\nindex of alpha=3.043 (+0.027, -0.580).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 1.47 (+0.33, -0.24). The\nbest-fitting absorption column is  consistent with the Galactic value\nof 1.3 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed\n(unabsorbed) 0.3-10 keV flux conversion factor deduced from this\nspectrum  is 3.7 x 10^-11 (3.8 x 10^-11) erg cm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     1.3 (+/-6.6) x 10^20 cm^-2\nGalactic foreground: 1.3 x 10^20 cm^-2\nExcess significance: <1.6 sigma\nPhoton index:\t     1.47 (+0.33, -0.24)\n\nIf the light curve continues to decay with a power-law decay index of\n3.043, the count rate at T+24 hours will be 0.014 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.3 x\n10^-13 (5.3 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/00021707.\nThe results of the full analysis of the tiled XRT observations are\navailable at https://www.swift.ac.uk/xrt_products/TILED_GRB00127.\n\nThis circular is an official product of the Swift-XRT team.\n\n",
  "bibcode": "2024GCN.37337....1B",
  "circularId": 37337,
  "submittedHow": "email",
  "subject": "GRB 240828A: Swift-XRT afterglow detection",
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>"
}