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GCN Circular 30986

Subject
GRB 211025A: Swift detection of a burst
Date
2021-10-25T05:29:36Z (2 years ago)
From
Aaron Tohuvavohu at U Toronto <aaron.tohu@gmail.com>
J.D. Gropp (PSU), D. M. Palmer (LANL), B. Sbarufatti (PSU) and
A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 05:10:20 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 211025A (trigger=1081113).  Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 162.377, +31.557 which is
   RA(J2000) = 10h 49m 30s
   Dec(J2000) = +31d 33' 26"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty).  As is usual for an image trigger, the
immediately available BAT lightcurve is unclear, but there does
appear to be a peak between T+30 and T+64, with a peak count rate
of ~300 counts/s (15-350 kev) at ~38 s after the nominal trigger time.

The XRT began observing the field at 05:12:23.2 UT, 123.3 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 162.38427, 31.51343 which
is equivalent to:
   RA(J2000)  = 10h 49m 32.22s
   Dec(J2000) = +31d 30' 48.3"
with an uncertainty of 4.1 arcseconds (radius, 90% containment). This
location is 158 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. No spectrum from the promptly downlinked
event data is yet available to determine the column density.

The initial flux in the 2.5 s image was 5.36e-09 erg cm^-2 s^-1 (0.2-10
keV).

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 131 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image processing
FAILED because of no aspect solution. Results from the list of sources
generated on-board are not available at this time. No correction has been made
for the expected extinction corresponding to E(B-V) of 0.027.

Burst Advocate for this burst is J.D. Gropp (jdg44 AT psu.edu).
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/)
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