TITLE: GCN CIRCULAR NUMBER: 29226 SUBJECT: GRB 210102C: Swift detection of a burst DATE: 21/01/02 20:47:29 GMT FROM: David Palmer at LANL E. Troja (NASA/GSFC/UMCP), M. G. Bernardini (INAF-OAB), C. Gronwall (PSU), A. Y. Lien (GSFC/UMBC), A. Melandri (INAF-OAB), D. M. Palmer (LANL) and T. Sbarrato (INAF-OAB) report on behalf of the Neil Gehrels Swift Observatory Team: At 20:38:11 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 210102C (trigger=1015728). Swift did not slew due to an observing constraint. The BAT on-board calculated location is RA, Dec 235.737, -37.222 which is RA(J2000) = 15h 42m 57s Dec(J2000) = -37d 13' 19" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a double-peaked structure with a duration of about 100 sec. The peak count rate was ~3000 counts/sec (15-350 keV), at ~65 sec after the trigger. Due to a Sun observing constraint, Swift cannot slew to the BAT position until 15:14 UT on 2021 January 06. There will thus be no XRT or UVOT data for this trigger before this time. Burst Advocate for this burst is E. Troja (eleonora.troja 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/)