{
  "bibcode": "2007GCN..6431....1G",
  "body": "C. Guidorzi (Univ Bicocca&INAF-OAB), S. D. Barthelmy (GSFC),\nP. A. Evans (U Leicester), N. Gehrels (NASA/GSFC), C. Gronwall (PSU),\nC. B. Markwardt (GSFC/UMD), A. Moretti (INAF-OAB),\nP. T. O'Brien (U Leicester), K. L. Page (U Leicester),\nD. M. Palmer (LANL), P. Romano (Univ. Bicocca & INAF-OAB) and\nG. Tagliaferri (INAF-OAB) report on behalf of the Swift Team:\n\nAt 06:51:10 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 070521 (trigger=279935).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 242.669, +30.241 which is \n   RA(J2000)  =  16h 10m 41s\n   Dec(J2000) = +30d 14' 27\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve shows multiple peaks\nwith a duration of about 40 sec.  The peak count rate\nwas ~7000 counts/sec (15-350 keV), at ~20 sec after the trigger. \n\nThe XRT began taking data at 06:52:27 UT, 77 seconds after the BAT\ntrigger.  The XRT on-board centroid algorithm did not find a source in the\nimage and no prompt position is available.  However, the downlinked X-ray\nspectrum and lightcurve show that there is an X-ray object in the\nfield that appears to be fading. \nUsing prompt downlinked data, we find a position RA, Dec 242.6606, 30.2579 which is\n   RA(J2000)  = 16h10m 38.5s\n   Dec(J2000) = +30d 15' 28.3''\nwith an uncertainty of 4.0 arcsec (radius, 90% containment). \n\n\nUVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)\nfilter starting 81 seconds after the BAT trigger. No afterglow candidate has\nbeen found in the initial data products. The 2.7'x2.7' sub-image covers 25% of\nthe BAT error circle. The typical 3-sigma upper limit has been about 18.5 mag. \nThe 8'x8' region for the list of sources generated on-board covers 100% of the\nBAT error circle. The list of sources is typically complete to about 18 mag. No\ncorrection has been made for the expected extinction corresponding to E(B-V) of\n0.03.",
  "circularId": 6431,
  "createdOn": 1179731075000,
  "email": "scott@lheamail.gsfc.nasa.gov",
  "subject": "GRB 070521: Swift detection of a burst",
  "submitter": "Scott Barthelmy at NASA/GSFC  <scott@lheamail.gsfc.nasa.gov>",
  "eventId": "GRB 070521"
}