{
  "body": "M.A. Williams (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.\nLeicester), A.P. Beardmore (U. Leicester), M. Ferro (INAF-OAB), R.\nBrivio (INAF-OAB), A. D'Ai (INAF-IASFPA), S. Dichiara (PSU), J.A.\nKennea (PSU) and P.A. Evans report on behalf of the Swift-XRT team:\n\nWe have analysed 7.7 ks of XRT data for GRB 250530C, from 90 s to 52.0\nks after the   trigger. The data comprise 9 s in Windowed Timing (WT)\nmode (taken while Swift was slewing), with the remainder in Photon\nCounting (PC) mode. \n\nThe light curve can be modelled with a power-law decay with a decay\nindex of alpha=0.80 (+/-0.04).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 1.55 (+0.20, -0.19). The\nbest-fitting absorption column is  2.8 (+1.1, -0.9) x 10^21 cm^-2, in\nexcess of the Galactic value of 1.7 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 5.0 x 10^-11 (6.1 x 10^-11) erg\ncm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     2.8 (+1.1, -0.9) x 10^21 cm^-2\nGalactic foreground: 1.7 x 10^20 cm^-2\nExcess significance: 4.7 sigma\nPhoton index:\t     1.55 (+0.20, -0.19)\n\nIf the light curve continues to decay with a power-law decay index of\n0.80, the count rate at T+24 hours will be 0.012 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.0 x\n10^-13 (7.3 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/01319125.\n\nThis circular is an official product of the Swift-XRT team.\n",
  "bibcode": "2025GCN.40589....1W",
  "submittedHow": "email",
  "eventId": "GRB 250530C",
  "subject": "GRB 250530C: Swift-XRT refined Analysis",
  "createdOn": 1748691106856,
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "circularId": 40589
}