TITLE: GCN CIRCULAR NUMBER: 40894 SUBJECT: GRB 250702F: Swift detection of a burst with an optical counterpart DATE: 25/07/02 21:42:54 GMT FROM: Mike Siegel at PSU/Swift MOC <siegel@swift.psu.edu> N. J. Klingler (GSFC/UMBC/CRESSTII), A. D'Ai (INAF-IASFPA), R. Gupta (NASA GSFC), A. Y. Lien (U Tampa), T. M. Parsotan (GSFC) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 21:06:43.27 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250702F (trigger= 1329888). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 212.933, +16.699 which is RA(J2000) = 14h 11m 44s Dec(J2000) = 16d 41' 57" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multi-peaked structure with a duration of about 70 sec. The peak count rate was ~4000 counts/sec (15-350 keV), at ~38 sec after the trigger. The XRT began observing the field at 21:08:11.7 UT, 88.5 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 212.9378, 16.7475 which is equivalent to: RA(J2000) = 14h 11m 45.07s Dec(J2000) = +16d 44' 51.0" with an uncertainty of 4.8 arcseconds (radius, 90% containment). This location is 175 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy. The initial flux in the 2.5 s image was 5.48e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 97 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 14:11:44.69 = 212.93622 DEC(J2000) = +16:44:55.0 = 16.74861 with a 90%-confidence error radius of about 0.74 arc sec. This position is 6.7 arc sec. from the center of the XRT error circle. The estimated magnitude is 15.85 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.017. This burst is spatially and temporally coincident with the burst reported by Fermi GBM (GCN Circ. 40892). Burst Advocate for this burst is N. J. Klingler (noelklin AT umbc.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/40894. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...