{
  "submittedHow": "email",
  "submitter": "Simone Dichiara at Pennsylvania State University <sbd5667@psu.edu>",
  "eventId": "GRB 240418A",
  "subject": "GRB 240418A: Swift detection of a burst",
  "circularId": 36162,
  "body": "\nM. H. Siegel (PSU), S. Dichiara (PSU), J.D. Gropp (PSU),\nF. E. Marshall (NASA/GSFC), D. M. Palmer (LANL) and\nM. A. Williams (PSU) report on behalf of the Neil Gehrels Swift\nObservatory Team:\n\nAt 20:24:08 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 240418A (trigger=1222885).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 239.322, +23.607 which is \n   RA(J2000) = 15h 57m 17s\n   Dec(J2000) = +23d 36' 26\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed a complex\nstructure with a duration of at least 20 sec.  The peak count rate\nwas ~700 counts/sec (15-350 keV), at ~7 sec after the trigger. \n\nThe XRT began observing the field at 20:26:10.4 UT, 122.2 seconds after\nthe BAT trigger. Using promptly downlinked data we find an uncatalogued\nX-ray source located at RA, Dec 239.37228, 23.59581 which is equivalent\nto:\n   RA(J2000)  = 15h 57m 29.35s\n   Dec(J2000) = +23d 35' 44.9\"\nwith an uncertainty of 6.5 arcseconds (radius, 90% containment). This\nlocation is 170 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 consistent with the Galactic value of 5.26\nx 10^20 cm^-2 (Willingale et al. 2013). \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 125 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 none of\nthe XRT error circle. The 8'x8' region for the list of sources generated\non-board covers 100% of the XRT error circle. The list of sources is typically\ncomplete to about 18 mag. No correction has been made for the expected\nextinction corresponding to E(B-V) of 0.058. \n\nBurst Advocate for this burst is M. H. Siegel (siegel AT swift.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/)\n\n",
  "bibcode": "2024GCN.36162....1S",
  "createdOn": 1713472604472
}