{
  "bibcode": "2007GCN..6438....1M",
  "body": "A. Moretti (INAF-OAB), P. Romano (Univ Bicocca&INAF-OAB),\nC. Guidorzi (Univ Bicocca&INAF-OAB), S.D. Vergani (DIAS-DCU)\nreport on behalf of the Swift team:\n\nWe have analysed the first three orbits of XRT data on GRB 070520B\n(Moretti et al., GCN Circ. 6425) with total observing times of 284 s\nin Windowed Timing mode (from T+104 to T+388 s) and 5.2 ks in Photon\nCounting mode (from T+388 s). The Photon Counting mode image provides\na refined XRT position at RA,DEC(J2000) = 121.87964,+57.60896, which is\n\nRA(J2000)  = 08h 07m 31.11s   \nDec(J2000) =+57d 36' 32.3\"\n\nwith an uncertainty of 4.0 arcsec (radius, 90% containment). This is\n1.0 arcsec from the initial X-ray position, and 76 arcsec from the\nrefine BAT position (Sakamoto et al., GCN Circ. 6429).\n\nThe XRT light curve (LC) exhibits an initial mildly steep decay (slope\n2.5) in the interval (100,170) seconds from the trigger. An intense\nFRED-like flare is present between 170 and 390 seconds. In the second\nand third orbits the LC shows a decay with a slope is 1.0+/-0.3.\n\nThe first WT spectrum, extracted before the flare, can be fit with an\nabsorbed power law with a photon index of 2.5+/-0.2 and a column\ndensity of (2.1+/-0.4)E21 cm^-2 significantly in excess of the\nGalactic value (4.22E20 cm^-2; Dickey & Lockman, 1990). The mean WT\nspectrum, extracted during the flare, can be fit with an absorbed\npower law with a photon index of 2.6+/-0.1 and a column density of\n(2.5+/-0.2)E21 cm^-2 again significantly in excess of the Galactic\nvalue. The absorbed (unabsorbed) 0.3-10.0keV mean flare flux is\n9.4E-10 (2.1E-9) ergs cm^-2 s^-1.\nErrors are quoted at 90% confidence level.\n\nAssuming the source continues to decay at the present rate, we\npredict an XRT count rate of 1E-3 counts/s at T+24 hours,\nwhich corresponds to an unabsorbed flux of 5E-14 ergs cm^-2 s^-1.\n\nThis circular is an official product of the Swift XRT team.",
  "circularId": 6438,
  "createdOn": 1179744107000,
  "email": "alberto.moretti@brera.inaf.it",
  "subject": "GRB 070520B: Swift-XRT refined analysis",
  "submitter": "Alberto Moretti at Obs Brera Merate  <alberto.moretti@brera.inaf.it>",
  "eventId": "GRB 070520B"
}