Swift detection of a new SGR 1830-0645 or a short GRB 201010A

ATel #14083; K. L. Page (U Leicester), S. D. Barthelmy (GSFC), N. J. Klingler (PSU), N. P. M. Kuin (UCL-MSSL) and A. Y. Lien (GSFC/UMBC) report on behalf of the Neil Gehrels Swift Observatory Team
on 10 Oct 2020; 16:02 UT
Credential Certification: David M. Palmer (palmer@lanl.gov)

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This is a courtesy copy of GCN #28594 which is the publication of record for citation

At 14:49:24 UT on 2020-10-10, the Swift Burst Alert Telescope (BAT) triggered and located SGR 1830-0645 or GRB 201010A (trigger=999571). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 277.675, -6.758, which is
RA(J2000) = 18h 30m 42s
Dec(J2000) = -06d 45' 30"
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a single peak structure with a duration of no more than 0.128 sec. The peak count rate was ~1600 counts/sec (15-350 keV), at ~0 sec after the trigger.

The XRT began observing the field at 14:50:30.9 UT, 67.0 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 277.6702, -6.7550 which is equivalent to:
RA(J2000) = 18h 30m 40.85s
Dec(J2000) = -06d 45' 18.0" with an uncertainty of 2.2 arcseconds (radius, 90% containment). This location is 20 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.

A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 1.11 x 10^22 cm^-2 (Willingale et al. 2013).

UVOT took a finding chart exposure of 150 seconds with the White filter starting 71 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. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the sub-image. 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.

Due to its short duration (BAT trigger duration of 8 ms, although the immediately available lightcurve is only available at 128 ms resolution), the soft spectrum (not visible above 50 keV) and its location in the Galactic bulge near the plane (lon,lat) = (24.5, 1.5) we suspect that this event may be a new Soft Gamma Repeater, which we would name SGR 1830-0645.

Burst Advocate for this burst is K. L. Page (klp5 AT leicester.ac.uk). 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/ )

This is a courtesy copy of GCN #28594 which is the publication of record for citation