{
  "bibcode": "2024GCN.36443....1S",
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "eventId": "GRB 240511A",
  "createdOn": 1715503073335,
  "subject": "GRB 240511A: Swift-XRT refined Analysis",
  "submittedHow": "email",
  "body": "C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB),\nJ.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), D.N. Burrows (PSU), K.L.\nPage (U. Leicester), A.P. Beardmore (U. Leicester) and P.A. Evans\nreport on behalf of the Swift-XRT team:\n\nWe have analysed 8.5 ks of XRT data for GRB 240511A, from 94 s to 36.0\nks after the  BAT trigger. The data comprise 345 s in Windowed Timing\n(WT) mode (the first 6 s were taken while Swift was slewing) with the\nremainder in Photon Counting (PC) mode. The best available XRT position\n (using the promptly downlinked event data, the XRT-UVOT alignment and\nmatching UVOT field sources to the USNO-B1 catalogue) is RA, Dec =\n336.67568, 8.51317 which is equivalent to:\n\nRA (J2000): 22 26 42.16\nDec(J2000): +08 30 47.4\n\nwith an uncertainty of 1.9 arcsec (radius, 90% confidence).\n\nThe late-time light curve (from T0+5.2 ks) can be modelled with a\npower-law decay with a decay index of alpha=0.76 (+/-0.10).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 2.07 (+/-0.04). The\nbest-fitting absorption column is  2.60 (+/-0.16) x 10^21 cm^-2, in\nexcess of the Galactic value of 8.5 x 10^20 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 2.08 (+0.16, -0.15)\nand a best-fitting absorption column of 1.6 (+0.5, -0.4) x 10^21 cm^-2.\nThe counts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum  is 3.4 x 10^-11 (4.6 x 10^-11) erg cm^-2\ncount^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     1.6 (+0.5, -0.4) x 10^21 cm^-2\nGalactic foreground: 8.5 x 10^20 cm^-2\nExcess significance: 2.8 sigma\nPhoton index:\t     2.08 (+0.16, -0.15)\n\nIf the light curve continues to decay with a power-law decay index of\n0.76, the count rate at T+24 hours will be 0.030 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.0 x\n10^-12 (1.4 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/01227767.\n\nThis circular is an official product of the Swift-XRT team.\n",
  "circularId": 36443
}