{
  "bibcode": "2015GCN.17515....1L",
  "body": "A. Y. Lien (GSFC/UMBC), D. N. Burrows (PSU), M. M. Chester (PSU),\nJ. R. Cummings (NASA/UMBC), M. De Pasquale (INAF-IASFPA),\nA. Maselli (INAF-IASFPA), K. L. Page (U Leicester),\nD. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the\nSwift Team:\n\nAt 19:38:04 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 150301B (trigger=633180).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 89.157, -57.977 which is \n   RA(J2000) = 05h 56m 38s\n   Dec(J2000) = -57d 58' 37\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed a single-peaked\nstructure with a duration of about 20 sec.  The peak count rate\nwas ~4000 counts/sec (15-350 keV), at ~1 sec after the trigger. \n\nThe XRT began observing the field at 19:39:26.4 UT, 82.4 seconds after\nthe BAT trigger. Using promptly downlinked data we find an uncatalogued\nX-ray source located at RA, Dec 89.16636, -57.97051 which is equivalent\nto:\n   RA(J2000)  = 05h 56m 39.93s\n   Dec(J2000) = -57d 58' 13.8\"\nwith an uncertainty of 3.6 arcseconds (radius, 90% containment). This\nlocation is 29 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 consistent with the Galactic value of 6.16\nx 10^20 cm^-2 (Willingale et al. 2013). \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 85 seconds after the BAT trigger. There is a candidate afterglow in\nthe rapidly available 2.7'x2.7' sub-image at\n  RA(J2000)  =\t05:56:39.86 =  89.16608\n  DEC(J2000) = -57:58:10.4  = -57.96956\nwith a 90%-confidence error radius of about 0.61 arc sec. This position is 31.9\narc sec. from the center of the BAT error circle. The estimated magnitude is\n16.22 with a 1-sigma error of about  0.14. No correction has been made for the\nexpected extinction corresponding to E(B-V) of 0.08. \n\nBurst Advocate for this burst is A. Y. Lien (amy.y.lien AT 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": 17515,
  "createdOn": 1425239401000,
  "email": "palmer@lanl.gov",
  "subject": "GRB 150301B: Swift detection of a burst with an optical afterglow",
  "submitter": "David Palmer at LANL  <palmer@lanl.gov>",
  "eventId": "GRB 150301B"
}