TITLE: GCN CIRCULAR NUMBER: 39938 SUBJECT: GRB 250330A: Swift detection of a burst DATE: 25/03/30 06:28:16 GMT FROM: K.L. Page at U Leicester S. B. Cenko (GSFC), K. L. Page (U Leicester) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 06:07:38 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250330A (trigger=1299776). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 252.790, -86.870 which is RA(J2000) = 16h 51m 10s Dec(J2000) = -86d 52' 11" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single peak structure with a duration of about 10 sec. The peak count rate was ~5800 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 06:08:51.3 UT, 73.2 seconds after the BAT trigger. Due to the proximity of Swift to the SAA, XRT centroided on a cosmic ray. Given the short visibility window, no other data are available at this time. UVOT data are not available at this time. Although this trigger occurred while Swift was close to the SAA, the BAT light-curve shows a definite peak, and Fermi-GBM also triggered at the same time. Burst Advocate for this burst is S. B. Cenko (brad.cenko AT nasa.gov). 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/)