{
  "bibcode": "2022GCN.31820....1K",
  "body": "N. J. Klingler (GSFC/UMBC/CRESSTII), E. Ambrosi (INAF-IASFPA),\nV. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), J.D. Gropp (PSU),\nH. A. Krimm (NSF), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL),\nT. M. Parsotan (GSFC/UMBC/CRESSTII) and T. Sakamoto (AGU) report on\nbehalf of the Neil Gehrels Swift Observatory Team:\n\nAt 20:42:42 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 220403B (trigger=1101053).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 191.025, +89.170 which is \n   RA(J2000) = 12h 44m 06s\n   Dec(J2000) = +89d 10' 13\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed a single-peaked\nstructure with a duration of about 30 sec and a possible precursor just before. \nThe peak count rate was ~2800 counts/sec (15-350 keV), at ~0 sec after the trigger. \n\nThe XRT began observing the field at 20:44:18.9 UT, 96.3 seconds after\nthe BAT trigger. Using promptly downlinked data we find a bright,\nuncatalogued X-ray source located at RA, Dec 191.50031, 89.18362 which\nis equivalent to:\n   RA(J2000)  = 12h 46m 00.07s\n   Dec(J2000) = +89d 11' 01.0\"\nwith an uncertainty of 3.9 arcseconds (radius, 90% containment). This\nlocation is 54 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 consistent with the Galactic value of 1.20\nx 10^21 cm^-2 (Willingale et al. 2013). \n\nThe initial flux in the 2.5 s image was 4.65e-10 erg cm^-2 s^-1 (0.2-10\nkeV). \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 105 seconds after the BAT trigger. There is a candidate afterglow in\nthe rapidly available 2.7'x2.7' sub-image at\n  RA(J2000)  =\t12:45:53.30 = 191.47207\n  DEC(J2000) = +89:11:06.6  =  89.18518\nwith a 90%-confidence error radius of about 0.67 arc sec. This position is 6.0\narc sec. from the center of the XRT error circle. The estimated magnitude is\n19.80 with a 1-sigma error of about  0.17. No correction has been made for the\nexpected extinction corresponding to E(B-V) of 0.208. \n\nBurst Advocate for this burst is N. J. Klingler (noelklin AT umbc.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": 31820,
  "createdOn": 1649019286000,
  "email": "hkrimm@nsf.gov",
  "subject": "GRB 220403B: Swift detection of a burst with an optical counterpart",
  "submitter": "Hans Krimm at NSF/NASA-GSFC  <hkrimm@nsf.gov>",
  "eventId": "GRB 220403B"
}