{
  "bibcode": "2023GCN.33378....1D",
  "body": "S. Dichiara (PSU), J.D. Gropp (PSU), D. M. Palmer (LANL) and\nT. M. Parsotan (GSFC/UMBC/CRESSTII) report on behalf of the Neil\nGehrels Swift Observatory Team:\n\nAt 05:50:50 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 230228A (trigger=1156572).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 18.403, +44.489 which is \n   RA(J2000) = 01h 13m 37s\n   Dec(J2000) = +44d 29' 19\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed a single symmetrical\npeak structure with a duration of about 1.5 sec.  The peak count rate\nwas ~2000 counts/sec (15-350 keV), at ~0 sec after the trigger. \n\nThe XRT began observing the field at 05:52:49.2 UT, 119.0 seconds after\nthe BAT trigger. Using promptly downlinked data we find a fading,\nuncatalogued X-ray source located at RA, Dec 18.37776, 44.48321 which\nis equivalent to:\n   RA(J2000)  = 01h 13m 30.66s\n   Dec(J2000) = +44d 28' 59.6\"\nwith an uncertainty of 3.7 arcseconds (radius, 90% containment). This\nlocation is 68 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. \n\nA power-law fit to a spectrum formed from promptly downlinked event\ndata gives a column density consistent with the Galactic value of 9.72\nx 10^20 cm^-2 (Willingale et al. 2013). \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 122 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\n0.085. \n\nBurst Advocate for this burst is S. Dichiara (simonedichiara55 AT gmail.com). \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": 33378,
  "createdOn": 1677564209000,
  "email": "palmer@lanl.gov",
  "subject": "GRB 230228A: Swift detection of a possibly short burst",
  "submitter": "David Palmer at LANL  <palmer@lanl.gov>",
  "eventId": "GRB 230228A"
}