TITLE: GCN CIRCULAR NUMBER: 26953 SUBJECT: GRB 200131A: Swift detection of a burst with an optical counterpart DATE: 20/01/31 22:53:30 GMT FROM: Jamie A. Kennea at PSU/Swift-XRT B. Sbarufatti (PSU), D. N. Burrows (PSU), J.D. Gropp (PSU), J. A. Kennea (PSU), N. J. Klingler (PSU), S. Laha (GSFC/UMBC/CRESST), A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC), M. H. Siegel (PSU) and A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift Observatory Team: At 22:41:15 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 200131A (trigger=953689). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 3.095, +51.124 which is RA(J2000) = 00h 12m 23s Dec(J2000) = +51d 07' 25" 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 5 sec. There might be a small pulse at T+30 s. The peak count rate was ~60000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 22:42:24.7 UT, 68.7 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 3.0942, 51.1158 which is equivalent to: RA(J2000) = 00h 12m 22.61s Dec(J2000) = +51d 06' 56.9" with an uncertainty of 4.9 arcseconds (radius, 90% containment). This location is 29 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 3.76e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 77 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 00:12:22.57 = 3.09403 DEC(J2000) = +51:07:00.4 = 51.11678 with a 90%-confidence error radius of about 0.61 arc sec. This position is 3.6 arc sec. from the center of the XRT error circle. The estimated magnitude is 15.44 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.17. Burst Advocate for this burst is B. Sbarufatti (bxs60 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/)