[vsnet-grb-info 26494] Swift detection of a new SGR 1830-0645 or a short GRB 201010A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  28594
SUBJECT: Swift detection of a new SGR 1830-0645 or a short GRB 201010A
DATE:    20/10/10 15:16:16 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at milkyway.gsfc.nasa.gov>

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:

At 14:49:24 UT, 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/)