TITLE: GCN CIRCULAR NUMBER: 29487 SUBJECT: GRB 210212A: Swift detection of a burst DATE: 21/02/12 04:50:37 GMT FROM: David Palmer at LANL E. Troja (NASA/GSFC/UMCP), J. A. Kennea (PSU), N. J. Klingler (PSU), H. A. Krimm (NSF), F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL), B. Sbarufatti (PSU), M. H. Siegel (PSU) and A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift Observatory Team: At 04:25:18 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 210212A (trigger=1032183). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 72.261, +7.234 which is RA(J2000) = 04h 49m 03s Dec(J2000) = +07d 14' 01" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a structure with a duration of about 50 sec. The peak count rate was ~1200 counts/sec (15-350 keV), at ~6 sec after the trigger. The XRT began observing the field at 04:27:00.9 UT, 103.0 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source with an enhanced position: RA, Dec 72.2666, 7.2693 which is equivalent to: RA(J2000) = 04h 49m 03.99s Dec(J2000) = +07d 16' 09.5" with an uncertainty of 3.8 arcseconds (radius, 90% containment). This location is 128 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. We cannot determine whether the source is fading at the present time. No spectrum from the promptly downlinked event data is yet available to determine the column density. The initial flux in the 2.5 s image was 9.74e-10 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 250 seconds with the U filter starting 270 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 0.094. 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/)