{
  "bibcode": "2023GCN.33527....1G",
  "body": "J.D. Gropp (PSU), S. Dichiara (PSU),\nR. A. J. Eyles-Ferris (U Leicester), N. P. M. Kuin (UCL-MSSL),\nF. E. Marshall (NASA/GSFC), M. J. Moss (GWU),\nK. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU)\nreport on behalf of the Neil Gehrels Swift Observatory Team:\n\nAt 14:54:48 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 230328B (trigger=1162001).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 290.986, +80.016 which is \n   RA(J2000) = 19h 23m 57s\n   Dec(J2000) = +80d 00' 58\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed a complex GRB\nstructure with a duration of about 20 sec, followed by a bright flaring\nafterglow visible below 25 keV for at least 200 s.  The peak count rate\nwas ~4375 counts/sec (15-350 keV), at ~0 sec after the trigger. \n\nThe XRT began observing the field at 14:56:38.8 UT, 110.3 seconds after\nthe BAT trigger. Using promptly downlinked data we find a fading,\nuncatalogued X-ray source located at RA, Dec 291.00418, 80.00951 which\nis equivalent to:\n   RA(J2000)  = 19h 24m 01.00s\n   Dec(J2000) = +80d 00' 34.2\"\nwith an uncertainty of 3.6 arcseconds (radius, 90% containment). This\nlocation is 25 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 in excess of the Galactic value (6.28 x\n10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.6\n(+1.76/-1.56) x 10^21 cm^-2 (90% confidence). \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 114 seconds after the BAT trigger. There is a candidate afterglow in\nthe rapidly available 2.7'x2.7' sub-image at\n  RA(J2000)  =\t19:24:01.84 = 291.00765\n  DEC(J2000) = +80:00:34.5  =  80.00959\nwith a 90%-confidence error radius of about 0.62 arc sec. This position is 0.7\narc sec. from the center of the XRT error circle. The estimated magnitude is\n18.22 with a 1-sigma error of about  0.15. No correction has been made for the\nexpected extinction corresponding to E(B-V) of 0.070. \n\nBurst Advocate for this burst is J.D. Gropp (jdg44 AT psu.edu). \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": 33527,
  "createdOn": 1680015995000,
  "email": "palmer@lanl.gov",
  "subject": "GRB 230328B: Swift detection of a burst with an optical afterglow",
  "submitter": "David Palmer at LANL  <palmer@lanl.gov>",
  "eventId": "GRB 230328B"
}