{
  "bibcode": "2008GCN..7875....1M",
  "body": "J. Mao, C. Guidorzi, F. Pasotti (INAF-OAB) and C. B. Markwardt \n(CRESST/GSFC/UMD),\nreport on behalf of the Swift-XRT team:\n\nThe Swift-XRT began observing GRB 080613B (trigger=313954, Markwardt et\nal., GCN Circ. 7873) in Windowed Timing (WT) mode, 76 s after the BAT\ntrigger. The data of the first orbit consist of 149 s in Windowed Timing\nmode and 794 s in Photon Counting mode.\n\nUsing 757 s of overlapping XRT Photon Counting mode and UVOT data, we find\nan astrometrically corrected X-ray position (using the XRT-UVOT \nalignment and\nmatching UVOT field sources to the USNO-B1 catalogue):\nRA, Dec = 173.79773, -7.10501 which is equivalent to:\n\nRA (J2000): 11 35 11.46\nDec (J2000): -07 06 18.0\n\nwith an uncertainty of 2.3 arcsec (radius, 90% confidence).\n\nThe light curve from 76 to 219 s can be modelled  as a power law with a \nphoton index\nof 2.15 +/- 0.11 (90%), followed by a sudden drop of about 2 orders of \nmagnitudes up to ~400 s,\nafter which the decay resumes a value around 1.5.\n\nThe WT mode spectrum spanning from 76 to 219 s can be fit by a\npower-law model, with a spectral photon index of 1.17 +/- 0.07 and an \nabsorbing column\ndensity of 3.7 (-2.0, +2.3)e20 cm^-2 , consistent with the average Galactic\none, 3.2e20 cm^-2.\n\nThe corresponding observed (unabsorbed) 0.3-10 keV flux is 1.05e-9 (1.09e-9)\nerg cm^-2 s^-1.\n\nIf the burst continues to decay at the same rate, we predict an\nXRT count rate of 6e-5 count/s at T+24 hours, which corresponds\nto an observed 0.3-10 keV flux of approximately 3.5e-15 erg cm^-2 s^-1.\nHowever, we caution about this prediction due to the presently large\nuncertainty on the decay rate.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 7875,
  "createdOn": 1213380673000,
  "email": "cristiano.guidorzi@brera.inaf.it",
  "subject": "GRB 080613B: Swift-XRT refined analysis",
  "submitter": "Cristiano Guidorzi at INAF-OAB  <cristiano.guidorzi@brera.inaf.it>",
  "eventId": "GRB 080613B"
}