TITLE: GCN CIRCULAR NUMBER: 37397 SUBJECT: GRB 240905E: Swift detection of a burst DATE: 24/09/05 18:46:08 GMT FROM: Tyler Parsotan at NASA GSFC <tyler.parsotan@nasa.gov> S. Dichiara (PSU), J. J. DeLaunay (PSU), R. Gupta (NASA GSFC), J. A. Kennea (PSU), K. L. Page (U Leicester), T. M. Parsotan (GSFC) and M. A. Williams (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 18:26:03 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 240905E (trigger=1252695). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 345.799, +35.495 which is RA(J2000) = 23h 03m 12s Dec(J2000) = +35d 29' 42" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex double-peaked structure with a duration of about 10 sec. The peak count rate was ~3000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 18:27:50.0 UT, 106.5 seconds after the BAT trigger. Using promptly downlinked data we find a bright X-ray source located at RA, Dec 345.80347, 35.52378 which is equivalent to: RA(J2000) = 23h 03m 12.83s Dec(J2000) = +35d 31' 25.6" with an uncertainty of 4.3 arcseconds (radius, 90% containment). This location is 104 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. We cannot determine whether the source is fading at the present time. This position is 22.7 arcseconds from that of a known X-ray source: 1RXS J230313.6+353105 in the ROSAT RASSFSC catalogue. Assuming a typical GRB power-law spectrum (NH=3e21 cm^-2, gamma=2), the catalogue entry for this object is equivalent to a 0.2-10 keV flux of 1.4e-12 erg cm^-2 s^-1; the flux in the 2.5 s XRT image was 1.11e-09 erg cm^-2 s^-1. No spectrum from the promptly downlinked event data is yet available to determine the column density. UVOT took a finding chart exposure of 150 seconds with the White filter starting 115 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers none of the XRT error circle. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.076. We note that the X-ray source is near to a catalogued X-ray source, 1RXS J230313.6+353105. However, this is not a known transient source, and is likely a chance coincidence. Therefore at this time, we believe that this is a GRB. Burst Advocate for this burst is S. Dichiara (sbd5667 AT psu.edu). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/) View this GCN Circular online at https://gcn.nasa.gov/circulars/37397. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...