TITLE:   GCN CIRCULAR
NUMBER:  45690
SUBJECT: GRB 260922A: Swift detection of a burst
DATE:    26/09/22 10:19:04 GMT
FROM:    K.L. Page at U Leicester <klp5@leicester.ac.uk>

K. L. Page (U Leicester), P. A. Evans (U Leicester) and
A. Y. Lien (U Tampa) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 10:00:39.44 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 260922A (trigger=1512686).  Swift slewed immediately to the
burst.
The BAT on-board calculated location is
RA, Dec = 227.904, +14.207 deg,  which is
   RA(J2000) = 15h 11m 37s
   Dec(J2000) = 14d 12' 26"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of about 50 sec.  The peak count rate
was ~3000 counts/sec (15-350 keV), at ~1 sec after the trigger.

The XRT began observing the field at 10:02:28.3 UT, 108.9 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
227.90885, 14.21924 which is equivalent to:
   RA(J2000)  = 15h 11m 38.12s
   Dec(J2000) = +14d 13' 09.3"
with an uncertainty of 2.4 arcseconds (radius, 90% containment). This
location is 47 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 in excess of the Galactic value (2.88 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 5.1
(+2.88/-2.57) x 10^21 cm^-2 (90% confidence).

The initial flux in the 2.5 s image was 2.31e-09 erg cm^-2 s^-1 (0.2-10
keV).

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 122 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 19.6 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 mag. No correction has been made
for extinction.

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/)