TITLE: GCN CIRCULAR NUMBER: 40988 SUBJECT: GRB 250706A: Swift detection of a burst DATE: 25/07/06 16:05:46 GMT FROM: Mike Moss at NASA GSFC <mikejmoss3@gmail.com> M. J. Moss (GSFC), E. Ambrosi (INAF-IASFPA), R. Gupta (NASA GSFC), J. A. Kennea (PSU), A. Melandri (INAF-OAR), K. L. Page (U Leicester) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 15:48:30.96 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250706A (trigger=1330958). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 284.007, +32.287 which is RA(J2000) = 18h 56m 1.6s Dec(J2000) = +32d 17' 13" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 35 sec. The peak count rate was ~750 counts/sec (15-350 keV), at ~7 sec after the trigger. The XRT began observing the field at 15:50:53.1 UT, 142.2 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 284.01755, 32.32120 which is equivalent to: RA(J2000) = 18h 56m 04.21s Dec(J2000) = +32d 19' 16.3" with an uncertainty of 3.5 arcseconds (radius, 90% containment). This location is 127 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. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 1.20 x 10^21 cm^-2 (Willingale et al. 2013). The initial flux in the 2.5 s image was 5.25e-10 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 250 seconds with the U filter starting 147 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 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.2 mag. 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 18.0 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.093. Burst Advocate for this burst is M. J. Moss (mikejmoss3 AT gmail.com). 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/40988. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...