{
  "bibcode": "2009GCN.10256....1P",
  "body": "C. Pagani (PSU), A. P. Beardmore (U Leicester),\nP. A. Evans (U Leicester), C. Gronwall (PSU),\nS. T. Holland (CRESST/USRA/GSFC), N. P. M. Kuin (MSSL),\nC. B. Markwardt (CRESST/GSFC/UMD), P. T. O'Brien (U Leicester),\nK. L. Page (U Leicester), A. Rowlinson (U Leicester),\nM. Stamatikos (OSU/NASA/GSFC), G. Tagliaferri (INAF-OAB) and\nL. Vetere (PSU) report on behalf of the Swift Team:\n\nAt 09:49:57 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 091208B (trigger=378559).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 29.410, +16.883 which is \n   RA(J2000) = 01h 57m 39s\n   Dec(J2000) = +16d 52' 57\"\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 15 sec.  The peak count rate\nwas ~9100 counts/sec (15-350 keV), at ~8 sec after the trigger. \n\nThe XRT began observing the field at 09:51:53.1 UT, 115.2 seconds after\nthe BAT trigger. Using promptly downlinked data we find a fading,\nuncatalogued X-ray source with an enhanced position: RA, Dec 29.3920,\n16.8899 which is equivalent to:\n   RA(J2000)  = 01h 57m 34.09s\n   Dec(J2000) = +16d 53' 23.6\"\nwith an uncertainty of 2.1 arcseconds (radius, 90% containment). This\nlocation is 66 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. \n\nA power-law fit to a spectrum formed from promptly downlinked event\ndata gives a column density in excess of the Galactic value (4.85e+20\ncm^-2, Kalberla et al. 2005), with an excess column of 3.3\n(+1.52/-1.28) x 10^21 cm^-2 (90% confidence). \n\nUVOT took a finding chart exposure of 150 seconds with the White\nfilter  starting 119 seconds after the BAT trigger.    There is an\nafterglow in the rapidly available 2.7'x2.7' sub-image at \n   RA(J2000)  =    01:57:34.06 = 29.39193 \n   DEC(J2000) =   +16:53:22.7  = 16.88963  with a 90%-confidence\nerror radius of about 0.6 arc sec. This position  is 0.67 arc sec. \nfrom the center of the XRT error circle. The estimated  magnitude is\n17.9. No correction has been made for the expected extinction\ncorresponding to E(B-V) of 0.05.     There is a bright afterglow\ncandidate consistent with the XRT position. \n\nBurst Advocate for this burst is C. Pagani (pagani AT astro.psu.edu). \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": 10256,
  "createdOn": 1260267239000,
  "email": "pagani@astro.psu.edu",
  "subject": "GRB 091208B: Swift detection of a burst with an optical afterglow",
  "submitter": "Claudio Pagani at PSU/Swift-XRT  <pagani@astro.psu.edu>",
  "eventId": "GRB 091208B"
}