Swift Trigger 1033144: Detection of SGR 1830-0645

At 08:11:21 UT, the Swift Burst Alert Telescope (BAT) triggered and located the soft gamma repeater SGR 1830-0645 (trigger=1033144). Swift slewed immediately to the source. The BAT on-board calculated location is RA, Dec 277.646, -6.735 which is RA(J2000) = 18h 30m 35s Dec(J2000) = -06d 44' 05" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single-peaked structure with a duration of about 0.1 sec. The peak count rate was ~10000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 08:12:33.2 UT, 71.9 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 277.67287, -6.75438 which is equivalent to: RA(J2000) = 18h 30m 41.49s Dec(J2000) = -06d 45' 15.8" with an uncertainty of 4.2 arcseconds (radius, 90% containment). This location is 118 arcseconds from the BAT onboard position, within the BAT error circle, and consistent with the known location of SGR 1830-0645. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (1.11 x 10^22 cm^-2, Willingale et al. 2013), with an excess column of 2.7 (+4.47/-2.40) x 10^22 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 76 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 large, but uncertain, extinction expected. BAT most recently triggered on SGR 1830-0645 on 2021 Feb 13 (GCN 29500).