{
  "circularId": 35602,
  "createdOn": 1706009696825,
  "submittedHow": "email",
  "eventId": "GRB 240123A",
  "subject": "GRB 240123A: Swift detection of a burst with a possible optical counterpart",
  "body": "\nA. D'Ai (INAF-IASFPA), E. Ambrosi (INAF-IASFPA),\nV. D'Elia (SSDC & INAF-OAR), J.D. Gropp (PSU), J. A. Kennea (PSU),\nA. Y. Lien (U Tampa), A. Melandri (INAF-OAR),\nK. L. Page (U Leicester), T. M. Parsotan (GSFC/UMBC/CRESSTII) and\nB. Sbarufatti (INAF-OAB) report on behalf of the Neil Gehrels Swift\nObservatory Team:\n\nAt 11:05:46 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 240123A (trigger=1210276).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 199.319, +60.632 which is \n   RA(J2000) = 13h 17m 16s\n   Dec(J2000) = +60d 37' 53\"\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 25 sec.  The peak count rate\nwas ~500 counts/sec (15-350 keV), at ~5 sec after the trigger. \n\nThe XRT began observing the field at 11:08:08.6 UT, 141.8 seconds after\nthe BAT trigger. Using promptly downlinked data we find a bright,\nfading, uncatalogued X-ray source located at RA, Dec 199.34797,\n60.61894 which is equivalent to:\n   RA(J2000)  = 13h 17m 23.51s\n   Dec(J2000) = +60d 37' 08.2\"\nwith an uncertainty of 3.8 arcseconds (radius, 90% containment). This\nlocation is 69 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 (1.45 x\n10^20 cm^-2, Willingale et al. 2013), with an excess column of 2.7\n(+2.69/-2.33) x 10^21 cm^-2 (90% confidence). \n\nThe initial flux in the 2.5 s image was 7.30e-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 151 seconds after the BAT trigger. There is a candidate afterglow in\nthe rapidly available 2.7'x2.7' sub-image at\n  RA(J2000)  =\t13:17:23.25 = 199.3468\n  DEC(J2000) = +60:37:04.4  = 60.6179\nwith a 90%-confidence error radius of about 0.2 arc sec. This position is 4.3\narc sec. from the center of the XRT error circle. The estimated magnitude is\n19.9 with a 1-sigma error of about 0.2. No correction has been made for the\nexpected extinction. \n\nBurst Advocate for this burst is A. D'Ai (antonino.dai AT 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/)\n\n",
  "submitter": "Antonino D'Ai' at IASF-PA <antonino.dai@inaf.it>",
  "bibcode": "2024GCN.35602....1D"
}