{
  "bibcode": "2009GCN.10283....1K",
  "body": "H. A. Krimm (CRESST/GSFC/USRA), D. N. Burrows (PSU),\nP.A. Curran (MSSL-UCL), A. de Ugarte Postigo (INAF-OAB),\nN. Gehrels (NASA/GSFC), D. Grupe (PSU), C. Guidorzi (U Ferrara),\nS. T. Holland (CRESST/USRA/GSFC), E. A. Hoversten (PSU),\nN. P. M. Kuin (MSSL), J. Mao (INAF-OAB),\nR. Margutti (Univ Bicocca&OAB), C. B. Markwardt (CRESST/GSFC/UMD),\nF. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester),\nD. M. Palmer (LANL), J. L. Racusin (NASA/GSFC),\nP. Romano (INAF-IASFPA), B. Sbarufatti (INAF-IASFPA),\nM. H. Siegel (PSU), M. C. Stroh (PSU), E. Troja (NASA/GSFC/ORAU) and\nT. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team:\n\nAt 20:52:52 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 091221 (trigger=380311).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 55.754, +23.212 which is \n   RA(J2000) = 03h 43m 01s\n   Dec(J2000) = +23d 12' 42\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve shows a peak from T+0 to T+15\nseconds with a second, larger peak from T+15 to T+40. There is\nsome complexity in the light curve from A0535+262 (currently in outburst\nat ~5 Crabs of flux) in the Field Of View, but the GRB peaks are\ndistinguishable from the softer A0535+262 emission.  The peak count\nrate was 3500 counts/sec at ~30 sec after the trigger. \n\nThe XRT began observing the field at 20:54:04.7 UT, 72.4 seconds after\nthe BAT trigger. Using promptly downlinked data we find a bright,\nfading, uncatalogued X-ray source located at RA, Dec 55.79831, 23.24030\nwhich is equivalent to:\n   RA(J2000)  = 03h 43m 11.59s\n   Dec(J2000) = +23d 14' 25.1\"\nwith an uncertainty of 4.2 arcseconds (radius, 90% containment). This\nposition may be improved as more data are received; the latest position\nis available at http://www.swift.ac.uk/sper.  This position is \n170 arcseconds from the BAT position. \n\nA power-law fit to a spectrum formed from promptly downlinked event\ndata gives a column density consistent with the Galactic value of\n1.09e+21 cm^-2 (Kalberla et al. 2005). \n\nThe initial flux in the 2.5 s image was 1.47e-09 erg cm^-2 s^-1 (0.2-10\nkeV). \n\nUVOT took a finding chart exposure of 150 seconds with the White\nfilter  starting 79 seconds after the BAT trigger. No credible\nafterglow candidate has  been found in the initial data products. The\n2.7'x2.7' sub-image covers 100% of  the XRT error circle. The typical\n3-sigma upper limit has been about 19.6 mag.  The 8'x8' region for the\nlist of sources generated on-board covers 100% of the  XRT error\ncircle. The list of sources is typically complete to about 18 mag. No \ncorrection has been made for the expected extinction corresponding to\nE(B-V) of  0.22.  We note the possibility of a faint source on the\nnorthern edge of the XRT error circle.  Further analysis is\nforthcoming. \n\nBurst Advocate for this burst is H. A. Krimm (krimm AT milkyway.gsfc.nasa.gov). \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": 10283,
  "createdOn": 1261430255000,
  "email": "palmer@lanl.gov",
  "subject": "GRB 091221: Swift detection of a burst",
  "submitter": "David Palmer at LANL  <palmer@lanl.gov>",
  "eventId": "GRB 091221"
}