{
  "bibcode": "2013GCN.14460....1M",
  "body": "A. Maselli (INAF-IASFPA), S. D. Barthelmy (GSFC),\nW. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU),\nN. Gehrels (NASA/GSFC), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL),\nA. Y. Lien (NASA/GSFC/ORAU), V. Mangano (INAF-IASFPA),\nC. B. Markwardt (NASA/GSFC), F. E. Marshall (NASA/GSFC),\nC. J. Mountford (U Leicester), D. M. Palmer (LANL) and\nM. H. Siegel (PSU) report on behalf of the Swift Team:\n\nAt 13:20:41 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 130427B (trigger=554635).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 314.891, -22.530 which is \n   RA(J2000)  =  20h 59m 34s\n   Dec(J2000) = -22d 31' 49\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve shows 3 peaks\nwith a total duration of about 40 sec.  The peak count rate\nwas ~2000 counts/sec (15-350 keV), at ~2 sec after the trigger. \n\nThe XRT began observing the field at 13:21:59.1 UT, 77.4 seconds after\nthe BAT trigger. Using promptly downlinked data we find a bright,\nuncatalogued X-ray source located at RA, Dec 314.89766, -22.54548 which\nis equivalent to:\n   RA(J2000)  = 20h 59m 35.44s\n   Dec(J2000) = -22d 32' 43.7\"\nwith an uncertainty of 4.4 arcseconds (radius, 90% containment). This\nlocation is 59 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 4.41\nx 10^20 cm^-2 (Kalberla et al. 2005). \n\nThe initial flux in the 2.5 s image was 1.15e-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 87 seconds after the BAT trigger. There is a candidate afterglow in\nthe list of sources generated on-board at\n  RA(J2000)  =\t20:59:35.64 = 314.89848\n  DEC(J2000) = -22:32:46.5  = -22.54626\nwith a 90%-confidence error radius of about 1.10 arc sec. This position is 7.6\narc sec. from the center of the XRT error circle. The estimated magnitude is\n17.19. No correction has been made for the expected extinction corresponding to\nE(B-V) of 0.07. \n\nBurst Advocate for this burst is A. Maselli (maselli AT ifc.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": 14460,
  "createdOn": 1367069518000,
  "email": "scott@milkyway.gsfc.nasa.gov",
  "subject": "GRB 130427B: Swift detection of a burst with optical counterpart",
  "submitter": "Scott Barthelmy at NASA/GSFC  <scott@milkyway.gsfc.nasa.gov>",
  "eventId": "GRB 130427B"
}