{
  "bibcode": "2017GCN.22191....1C",
  "body": "S. Campana (INAF-OAB), A. Beardmore (U. Leicester), A. D'Ai (INAF-IASFPA),\nV. D'Elia (ASDC), P. Evans (U. Leicester), J. Kennea (PSU), J.P. Osborne\n(U. Leicester), K.L. Page (U. Leicester), R.L.C. Starling (U. Leicester)\n\nreport on a preliminary analysis of the Swift XRT data. Swift XRT started\nobserving GRB171205A (D'Elia et al. 2017, GCN 22177) 145 s after the \ntrigger.\nXRT detected a bright X-ray source decreasing from ~80 c/s to ~10 c/s\nfrom 150 s to 400 s, remaining in Windowed Timing (WT) mode (Kennea et al.\n2017, GCN 22183).\nThe hardness ratio light curve does not imply appreciable spectral\nvariations during this time interval.\nWe fit the WT spectrum binned to 20 counts per energy bin with an absorbed\npower law (with the column density fixed to 5.9e20 cm-2, Willingale et al.\n2013, MNRAS 431 394).\nWe obtain a reduced chi2=1.23 (239 degrees of freedom, dof, and 9e-3 null\nhypothesis probability, nhp).\nThe inclusion of an intrinsic absorption component at the GRB redshift\n(z=0.0368, Izzo et al. 2017, GCN 22180) does not improve the fit, rather\nwe can only put a 90% confidence level upper limit of N_H(z)<0.3e20 cm-2.\n\nGiven the relatively low nhp of the fit we include a soft blackbody \ncomponent.\nThe fit improves considerably with kT_BB=0.10+-0.02 keV (90% c.l.) and\nequivalent radius R_BB~5e11 cm (for a source distance of 163 Mpc).\nThe fit is good with a reduced chi2=1.09 (237 dof and 0.15 nhp).\nF-test provides a probability for a chance improvement of 6e-8.\nThe 0.3-10 keV blackbody contribution to the total flux is ~4%.\n\nWe checked that the fit does not improve using different values for the\nGalactic column density (NH_DL=4.82e20 cm-2 or NH_Kalberla=4.91e20\ncm-2), reaching similar results.\nUsing a spectrum made from grade 0 events does not change the\nresults and the blackbody component is still significant.",
  "circularId": 22191,
  "createdOn": 1512581516000,
  "email": "sergio.campana@brera.inaf.it",
  "subject": "Possible blackbody component in the X-ray spectrum of GRB171205A",
  "submitter": "Sergio Campana at INAF-OAB  <sergio.campana@brera.inaf.it>",
  "eventId": "GRB 171205A"
}