{
  "submitter": "Jamie Kennea at Penn State U <jak51@psu.edu>",
  "eventId": "GRB 230420A",
  "subject": "GRB 230420A: Swift detection of a burst",
  "circularId": 33658,
  "body": "\nN. J. Klingler (GSFC/UMBC/CRESSTII), R. Brivio (INAF-OAB),\nR. A. J. Eyles-Ferris (U Leicester), J.D. Gropp (PSU),\nJ. A. Kennea (PSU), K. L. Page (U Leicester),\nT. M. Parsotan (GSFC/UMBC/CRESSTII), C. Salvaggio (INAF-OAB) and\nB. Sbarufatti (INAF-OAB) report on behalf of the Neil Gehrels Swift\nObservatory Team:\n\nAt 10:19:01 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 230420A (trigger=1164980).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 161.013, +32.087 which is \n   RA(J2000) = 10h 44m 03s\n   Dec(J2000) = +32d 05' 11\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed a complex\nstructure with a duration of about 30 sec.  The peak count rate\nwas ~800 counts/sec (15-350 keV), at ~1 sec after the trigger. \n\nThe XRT began observing the field at 10:20:32.9 UT, 91.8 seconds after\nthe BAT trigger. Using promptly downlinked data we find a bright,\nuncatalogued X-ray source with an enhanced position: RA, Dec 161.04899,\n32.10766 which is equivalent to:\n   RA(J2000)  = 10h 44m 11.76s\n   Dec(J2000) = +32d 06' 27.6\"\nwith an uncertainty of 1.9 arcseconds (radius, 90% containment). This\nlocation is 132 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\nhttps://www.swift.ac.uk/sper.  We cannot determine whether the source\nis 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 (1.71 x\n10^20 cm^-2, Willingale et al. 2013), with an excess column of 2.1\n(+2.19/-1.93) x 10^21 cm^-2 (90% confidence). \n\nThe initial flux in the 2.5 s image was 3.05e-09 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 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\n0.017. \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/)\n\n",
  "bibcode": "2023GCN.33658....1K",
  "createdOn": 1681986981951
}