TITLE: GCN CIRCULAR NUMBER: 29472 SUBJECT: GRB 210211A: Swift detection of a burst DATE: 21/02/11 09:00:56 GMT FROM: Phil Evans at U of Leicester E. Troja (NASA/GSFC/UMCP), P. A. Evans (U Leicester), H. A. Krimm (NSF), K. L. Page (U Leicester), B. Sbarufatti (PSU) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 08:43:18 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 210211A (trigger=1032024). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 269.433, -46.299 which is RA(J2000) = 17h 57m 44s Dec(J2000) = -46d 17' 57" 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 10 sec. The peak count rate was ~2500 counts/sec (15-350 keV), at ~4 sec after the trigger. The XRT began observing the field at 08:44:32.2 UT, 73.9 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 269.4374, -46.2660 which is equivalent to: RA(J2000) = 17h 57m 44.99s Dec(J2000) = -46d 15' 57.7" with an uncertainty of 3.4 arcseconds (radius, 90% containment). This location is 119 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. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (1.24 x 10^21 cm^-2, Willingale et al. 2013), with an excess column of 8.7 (+9.04/-6.57) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 77 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 none of the XRT error circle. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the region. No correction has been made for the expected extinction corresponding to E(B-V) of 0.126. 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/)