{
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "eventId": "GRB 240912A",
  "submittedHow": "email",
  "subject": "GRB 240912A: Swift-XRT refined Analysis",
  "bibcode": "2024GCN.37479....1B",
  "createdOn": 1726167053404,
  "circularId": 37479,
  "body": "D.N. Burrows (PSU), M. A. Williams (PSU), S. Dichiara (PSU), J.P.\nOsborne (U. Leicester), K.L. Page (U. Leicester), A. Melandri\n(INAF-OAR), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB) and P.A.\nEvans report on behalf of the Swift-XRT team:\n\nWe have analysed 6.9 ks of XRT data for GRB 240912A, from 99 s to 45.7\nks after the  BAT trigger. The data comprise 939 s in Windowed Timing\n(WT) mode (the first 5 s were taken while Swift was slewing) with the\nremainder in Photon Counting (PC) mode. \n\nThe late-time light curve (from T0+4.8 ks) can be modelled with a\npower-law decay with a decay index of alpha=0.82 (+/-0.07).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.925 (+/-0.020). The\nbest-fitting absorption column is  2.61 (+/-0.29) x 10^21 cm^-2, at a\nredshift of 1.234, in addition to the Galactic value of 5.6 x 10^20\ncm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index\nof 1.86 (+/-0.09) and a best-fitting absorption column of 9 (+11, -9) x\n10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux\nconversion factor deduced from this spectrum  is 3.6 x 10^-11 (4.1 x\n10^-11) erg cm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nGalactic foreground: 5.6 x 10^20 cm^-2\nIntrinsic column:    9 (+11, -9) x 10^20 cm^-2 at z=1.234\nPhoton index:\t     1.86 (+/-0.09)\n\nIf the light curve continues to decay with a power-law decay index of\n0.82, the count rate at T+24 hours will be 0.12 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.3 x\n10^-12 (4.9 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/01253910.\n\nThis circular is an official product of the Swift-XRT team.\n"
}