{
  "bibcode": "2010GCN.10712....1M",
  "body": "J. Mao (INAF-OAB), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),\nA. de Ugarte Postigo (INAF-OAB), J. M. Gelbord (PSU),\nS. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),\nH. A. Krimm (CRESST/GSFC/USRA), F. E. Marshall (NASA/GSFC),\nP. T. O'Brien (U Leicester), D. M. Palmer (LANL),\nP. Romano (INAF-IASFPA), B. Sbarufatti (INAF-OAB/IASFPA),\nM. H. Siegel (PSU), M. Stamatikos (OSU/NASA/GSFC),\nG. Tagliaferri (INAF-OAB) and E. Troja (NASA/GSFC/ORAU) report on\nbehalf of the Swift Team:\n\nAt 19:20:59 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 100504A (trigger=421124).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 255.572, -35.599 which is \n   RA(J2000) = 17h 02m 17s\n   Dec(J2000) = -35d 35' 55\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed a double-peaked\nstructure with a duration of about 30 sec.  The peak count rate\nwas ~2500 counts/sec (15-350 keV), at ~0 and ~10 sec after the trigger. \n\nThe XRT began observing the field at 19:22:02.1 UT, 62.6 seconds after\nthe BAT trigger. Using promptly downlinked data we find a bright, fading,\nuncatalogued X-ray source located at RA, Dec 255.57053, -35.58712 which\nis equivalent to:\n   RA(J2000)  = 17h 02m 16.93s\n   Dec(J2000) = -35d 35' 13.6\"\nwith an uncertainty of 4.1 arcseconds (radius, 90% containment). This\nlocation is 42 arcseconds from the BAT onboard position, within the BAT\nerror circle. This position may be improved as more data are received;\nthe latest position is available at http://www.swift.ac.uk/sper.  We\ncannot determine whether the source is fading at the present time. \n\nA power-law fit to a spectrum formed from promptly downlinked event\ndata gives a column density consistent with the Galactic value of\n3.61e+21 cm^-2 (Kalberla et al. 2005). \n\nThe initial flux in the 2.5 s image was 5.58e-09 erg cm^-2 s^-1 (0.2-10\nkeV). \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 71 seconds after the BAT trigger. No credible afterglow candidate has\nbeen found in the initial data products. The 2.7'x2.7' sub-image covers 100% of\nthe XRT error circle. Because of the density of catalogued stars, further\nanalysis is required to report an upper limit for any afterglow in the\nsub-image. The coverage of the XRT error circle by the 8'x8' region for the\nlist of sources generated on-board is uncertain because the large number of\nsources filled the available telemetry. Because of the density of catalogued\nstars, further analysis is required to report an upper limit for any afterglow\nin the region. No correction has been made for the large, but uncertain\nextinction expected. \n\nBurst Advocate for this burst is J. Mao (jirong.mao AT brera.inaf.it). \nPlease contact the BA by email if you require additional information\nregarding Swift followup of this burst. In extremely urgent cases, after\ntrying the Burst Advocate, you can contact the Swift PI by phone (see\nSwift TOO web site for information: http://www.swift.psu.edu/too.html.)",
  "circularId": 10712,
  "createdOn": 1273004943000,
  "email": "kennea@astro.psu.edu",
  "subject": "GRB 100504A: Swift detection of a burst",
  "submitter": "Jamie A. Kennea at PSU/Swift-XRT  <kennea@astro.psu.edu>",
  "eventId": "GRB 100504A"
}