{
  "bibcode": "2005GCN..3685....1R",
  "body": "P. Romano, A. Moretti (OAB), S. Vaughan (U. Leicester), L. A. Antonelli (OAR), S. Campana,\nG. Chincarini, S. Covino,D. Malesani, G. Tagliaferri (OAB), J. Osborne, R. Willingale,\nP.T. O'Brien, A. Levan, K. L. Page, M. R. Goad (U. Leicester), D. N. Burrows (PSU), report:\n\nAnalysis of the SWIFT XRT observation of GRB050724 in Photon Counting (PC) mode has revealed\nin the first orbit a diffuse X-ray halo centered around the afterglow location. The halo has\nthe form of complete ring which increases in radius through the observation and reached\nthe distance of ~100 arcsec during the first ~2000 sec after the trigger (T0). We can exclude\nit is due to instrumental effects. During the observation, which started ~343 seconds after\nthe burst trigger time (PC mode), the observed halo follows the expected behaviour of a \"light-echo\"\nas X-rays are scattered by dust in our Galaxy. From the radial expansion of the halo we estimate\na distance of 175 -/+ 50 pc to the dust (from the observer, 90% confidence interval).\n\nGRB 050724 is in the direction (Galactic) l = 350.37, b = 15.10 degrees, in which the density\nof interstellar medium is quite high as testified by both the neutral Hydrogen column density\nnH=1.5E21 cm-2 and the optical extiction E(B-V)=0.61 (A_V=2.029, A_K=0.225). This line of sight\nincludes the Scorpius Centaurus OB association at ~150-200 pc, consistent with the derived distance\nto the scattering medium.\n\nThe X-ray WT spectrum of GRB050724 is represented by a powerlaw with Photon index 1.93-/+0.05\nin the [0.5-10] keV band (as reported in GCN 3669; Romano et al.). The scattered X-ray light has,\nas expected, a softer spectrum with Photon index 3.2-0.8+1.0 (first orbit).\n\nMore information is posted at: http://www.merate.mi.astro.it/~romano/grb050724/index.html",
  "circularId": 3685,
  "createdOn": 1122415918000,
  "email": "romano@merate.mi.astro.it",
  "subject": "GRB 050724: dust-scattered X-ray halo detected in SWIFT/XRT observation",
  "submitter": "Pat Romano at OAB-Swift  <romano@merate.mi.astro.it>",
  "eventId": "GRB 050724"
}