{
  "bibcode": "2019GCN.26601....1B",
  "body": "M. G. Bernardini (INAF-OAB), S. D. Barthelmy (GSFC),\nP. D'Avanzo (INAF-OAB), J.D. Gropp (PSU), J. A. Kennea (PSU),\nN. J. Klingler (PSU), S Laha (GSFC/UMBC/CRESST),\nA. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC),\nA. Melandri (INAF-OAB), M. J. Moss (GWU) and A. Tohuvavohu (U Toronto)\nreport on behalf of the Neil Gehrels Swift Observatory Team:\n\nAt 00:01:19 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 191228A (trigger=946476).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 5.339, -8.670, which is \n   RA(J2000)  =  00h 21m 21s\n   Dec(J2000) = -08d 40' 12\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve is typically plain for an image trigger. \n\nThe XRT began observing the field at 00:03:23.2 UT, 123.4 seconds after\nthe BAT trigger. Using promptly downlinked data we find a bright,\nuncatalogued X-ray source located at RA, Dec 5.34755, -8.68313 which is\nequivalent to:\n   RA(J2000)  = 00h 21m 23.41s\n   Dec(J2000) = -08d 40' 59.3\"\nwith an uncertainty of 3.7 arcseconds (radius, 90% containment). This\nlocation is 56 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 https://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 in excess of the Galactic value (3.80 x\n10^20 cm^-2, Willingale et al. 2013), with an excess column of 4.4\n(+5.17/-3.93) x 10^21 cm^-2 (90% confidence). \n\nThe initial flux in the 0.1 s image was 1.26e-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 131 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. The typical 3-sigma upper limit has been about 19.6 mag. \nThe 8'x8' region for the list of sources generated on-board covers 100% of the\nXRT error circle. The list of sources is typically complete to about 18 mag. No\ncorrection has been made for the expected extinction corresponding to E(B-V) of\n0.04. \n\nBurst Advocate for this burst is M. G. Bernardini (grazia.bernardini 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/)",
  "circularId": 26601,
  "createdOn": 1577492313000,
  "email": "scott@milkyway.gsfc.nasa.gov",
  "subject": "GRB 191228A: Swift detection of a burst",
  "submitter": "Scott Barthelmy at NASA/GSFC  <scott@milkyway.gsfc.nasa.gov>",
  "eventId": "GRB 191228A"
}