{
  "bibcode": "2015GCN.17766....1P",
  "body": "K. L. Page (U Leicester), M. M. Chester (PSU),\nF. E. Marshall (NASA/GSFC), T. Sakamoto (AGU) and M. H. Siegel (PSU)\nreport on behalf of the Swift Team:\n\nAt 03:12:03 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 150428B (trigger=639278).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 292.654, +4.116 which is \n   RA(J2000) = 19h 30m 37s\n   Dec(J2000) = +04d 06' 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 30 sec.  The peak count rate\nwas ~1800 counts/sec (15-350 keV), at ~3 sec after the trigger. \n\nThe XRT began observing the field at 03:13:50.9 UT, 107.5 seconds after\nthe BAT trigger. Using promptly downlinked data we find a bright,\nfading, uncatalogued X-ray source located at RA, Dec 292.63764, 4.12529\nwhich is equivalent to:\n   RA(J2000)  = 19h 30m 33.03s\n   Dec(J2000) = +04d 07' 31.0\"\nwith an uncertainty of 3.7 arcseconds (radius, 90% containment). This\nlocation is 67 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 3.26\nx 10^21 cm^-2 (Willingale et al. 2013). \n\nThe initial flux in the 2.5 s image was 8.91e-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 117 seconds after the BAT trigger. No credible afterglow candidate has\nbeen found in the initial data products. The 2.7'x2.7' sub-image covers 100% of\nthe XRT error circle. Because of the density of catalogued stars, further\nanalysis is required to report an upper limit for any afterglow in the\nsub-image. The 8'x8' region for the list of sources generated on-board covers\n100% of the XRT error circle. Because of the density of catalogued stars,\nfurther analysis is required to report an upper limit for any afterglow in the\nregion. No correction has been made for the expected extinction corresponding\nto E(B-V) of 0.40. \n\nBurst Advocate for this burst is K. L. Page (klp5 AT leicester.ac.uk). \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": 17766,
  "createdOn": 1430192268000,
  "email": "klp5@leicester.ac.uk",
  "subject": "GRB 150428B: Swift detection of a burst",
  "submitter": "Kim Page at U.of Leicester  <klp5@leicester.ac.uk>",
  "eventId": "GRB 150428B"
}