{
  "bibcode": "2015GCN.18425....1M",
  "body": "A. Melandri (INAF-OAB), S. D. Barthelmy (GSFC),\nP. D'Avanzo (INAF-OAB), H. A. Krimm (CRESST/GSFC/USRA),\nN. P. M. Kuin (UCL-MSSL), D. M. Palmer (LANL) and\nB. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team:\n\nAt 01:29:12 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 151021A (trigger=660671).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 337.611, -33.199 which is \n   RA(J2000) = 22h 30m 27s\n   Dec(J2000) = -33d 11' 55\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed a complex multi-peaked\nstructure with a duration of at least 100 sec.  The peak count rate\nwas 2500 counts/sec (15-350 keV), at 10 sec after the trigger,\nalthough the lightcurve around the time of trigger is not\nimmediately available. \n\nThe XRT began observing the field at 01:30:43.2 UT, 90.7 seconds after\nthe BAT trigger. Using promptly downlinked data we find a bright,\nuncatalogued X-ray source located at RA, Dec 337.64619, -33.19907 which\nis equivalent to:\n   RA(J2000)  = 22h 30m 35.09s\n   Dec(J2000) = -33d 11' 56.7\"\nwith an uncertainty of 3.6 arcseconds (radius, 90% containment). This\nlocation is 106 arcseconds from the BAT onboard position, within the\nBAT error circle. This position may be improved as more data are\nreceived; the latest position is available at\nhttp://www.swift.ac.uk/sper. \n\nA power-law fit to a spectrum formed from promptly downlinked event\ndata gives a column destiny in excess of the Galactic value (1.13 x\n10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.9\n(+2.55/-2.23) x 10^21 cm^-2 (90% confidence). \n\nThe initial flux in the 0.1 s image was 2.76e-08 erg cm^-2 s^-1 (0.2-10\nkeV). \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 99 seconds after the BAT trigger. No credible afterglow candidate has\nbeen found in the initial data products. The 8'x8' region for the list of \nsources generated on-board covers 100% of the XRT error circle. The list \nof sources is typically complete to about 18 mag. No correction has \nbeen made for the expected extinction corresponding to E(B-V) of 0.01. \n\nBurst Advocate for this burst is A. Melandri (andrea.melandri AT brera.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": 18425,
  "createdOn": 1445393125000,
  "email": "scott@milkyway.gsfc.nasa.gov",
  "subject": "GRB 151021A: Swift detection of a burst",
  "submitter": "Scott Barthelmy at NASA/GSFC  <scott@milkyway.gsfc.nasa.gov>",
  "eventId": "GRB 151021A"
}