TITLE: GCN CIRCULAR NUMBER: 27254 SUBJECT: GRB 200228B: Swift detection of a burst DATE: 20/02/28 11:27:30 GMT FROM: Scott Barthelmy at NASA/GSFC S. Laha (GSFC/UMBC/CRESST), S. D. Barthelmy (GSFC), P. A. Evans (U Leicester), C. Gronwall (PSU), J.D. Gropp (PSU) and K. L. Page (U Leicester) report on behalf of the Neil Gehrels Swift Observatory Team: At 11:14:41 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 200228B (trigger=958733). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 252.026, +16.960, which is RA(J2000) = 16h 48m 06s Dec(J2000) = +16d 57' 37" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a single peak with a duration of about 25 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~5 sec after the trigger. The XRT began observing the field at 11:16:56.8 UT, 135.7 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 252.04730, 16.98505 which is equivalent to: RA(J2000) = 16h 48m 11.35s Dec(J2000) = +16d 59' 06.2" with an uncertainty of 5.7 arcseconds (radius, 90% containment). This location is 116 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. No spectrum from the promptly downlinked event data is yet available to determine the column density. UVOT data are unavailable at this time. Burst Advocate for this burst is S. Laha (sib.laha 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/)