{
  "bibcode": "2016GCN.19343....1K",
  "body": "H. A. Krimm (CRESST/GSFC/USRA), A. D'Ai (INAF-IASFPA),\nN. Gehrels (NASA/GSFC), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL),\nA. Y. Lien (GSFC/UMBC), A. Maselli (INAF-IASFPA), D. M. Palmer (LANL),\nJ. L. Racusin (NASA/GSFC) and M. H. Siegel (PSU) report on behalf of\nthe Swift Team:\n\nAt 23:26:11 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 160425A (trigger=684098).  Swift slewed to the burst\nafter a short delay due to an observing constraint. \nThe BAT on-board calculated location is \nRA, Dec 280.313, -54.359 which is \n   RA(J2000) = 18h 41m 15s\n   Dec(J2000) = -54d 21' 33\"\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 2 sec, followed by a \n50 second-long peak at T+250s.  There may also be a\nprecursor peak of ~100 s duration at T-380s. The peak count rate\nwas ~6000 counts/sec (15-350 keV), at ~0.2 sec after the trigger. \n\nThe XRT began observing the field at 23:29:34.7 UT, 203.4 seconds after\nthe BAT trigger. Using promptly downlinked data we find a fading,\nuncatalogued X-ray source with an enhanced position: RA, Dec 280.3274,\n-54.3601 which is equivalent to:\n   RA(J2000)  = 18h 41m 18.56s\n   Dec(J2000) = -54d 21' 36.2\"\nwith an uncertainty of 2.0 arcseconds (radius, 90% containment). This\nlocation is 30 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 (7.74 x\n10^20 cm^-2, Willingale et al. 2013), with an excess column of 4.5\n(+2.72/-2.31) x 10^21 cm^-2 (90% confidence). \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 208 seconds after the BAT trigger. There is a candidate afterglow in\nthe rapidly available 2.7'x2.7' sub-image at\n  RA(J2000)  =\t18:41:18.57 = 280.32738\n  DEC(J2000) = -54:21:36.1  = -54.36004\nwith a 90%-confidence error radius of about 0.68 arc sec. This position is 2.6\narc sec. from the center of the XRT error circle. The estimated magnitude is\n19.91 with a 1-sigma error of about  0.17. No correction has been made for the\nexpected extinction corresponding to E(B-V) of 0.06. \n\nIt is extremely unusual for a short GRB to have a long pulse\na few minutes later with much more fluence. \nIt is more common for a long GRB to have a short precursor pulse. \nFurther characterization of this event will require the full\ndownlinked data set. \n\nBurst Advocate for this burst is H. A. Krimm (hans.krimm 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": 19343,
  "createdOn": 1461629122000,
  "email": "hans.krimm@nasa.gov",
  "subject": "GRB 160425A: Swift detection of an unusual burst with an optical afterglow",
  "submitter": "Hans Krimm at NASA-GSFC  <hans.krimm@nasa.gov>",
  "eventId": "GRB 160425A"
}