{
  "bibcode": "2023GCN.33592....1B",
  "body": "A. P. Beardmore (U Leicester), C. Gronwall (PSU),\nA. Y. Lien (U Tampa), K. L. Page (U Leicester), T. Sakamoto (AGU),\nM. H. Siegel (PSU) and M. A. Williams (PSU) report on behalf of the\nNeil Gehrels Swift Observatory Team:\n\nAt 04:56:57 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 230409B (trigger=1163401). Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 329.530, +52.854 which is \n   RA(J2000) = 21h 58m 07s\n   Dec(J2000) = +52d 51' 15\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The immediately available BAT light curve\nstarts at ~ a few seconds after the BAT trigger time. The light \ncurve shows a small hump from ~50 to 100 s, however, further ground \ndata will be required to determine whether the hump is due to \nbackground fluctuation. \n\nThe XRT began observing the field at 04:58:38.0 UT, 101.2 seconds after\nthe BAT trigger. Using promptly downlinked data we find an uncatalogued\nX-ray source with an enhanced position: RA, Dec 329.51486, 52.83228\nwhich is equivalent to:\n   RA(J2000)  = 21h 58m 03.57s\n   Dec(J2000) = +52d 49' 56.2\"\nwith an uncertainty of 1.9 arcseconds (radius, 90% containment). This\nlocation is 84 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 consistent with the Galactic value of 7.56\nx 10^21 cm^-2 (Willingale et al. 2013). \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 386 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. No correction has been made for\nthe large, but uncertain, extinction expected. \n\nBurst Advocate for this burst is A. P. Beardmore (apb AT star.le.ac.uk). \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": 33592,
  "createdOn": 1681017705000,
  "email": "kimlpage1978@gmail.com",
  "subject": "GRB 230409B: Swift detection of a burst",
  "submitter": "Kim Page at U.of Leicester  <kimlpage1978@gmail.com>",
  "eventId": "GRB 230409B"
}