GCN Circular 26112

V. D'Elia (SSDC), E. Ambrosi (INAF-IASFPA), A. D'Ai (INAF-IASFPA),
J.D. Gropp (PSU), J. A. Kennea (PSU), N. J. Klingler (PSU),
H. A. Krimm (NSF), D. M. Palmer (LANL) and A. Tohuvavohu (U Toronto)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 21:23:31 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 191031D (trigger=932608).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 283.275, +47.639 which is 
   RA(J2000) = 18h 53m 06s
   Dec(J2000) = +47d 38' 19"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single peak
structure with a duration of about 0.4 sec.  The peak count rate
was ~18000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 21:24:59.8 UT, 88.8 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 283.2890,
47.6438 which is equivalent to:
   RA(J2000)  = 18h 53m 09.37s
   Dec(J2000) = +47d 38' 37.7"
with an uncertainty of 2.3 arcseconds (radius, 90% containment). This
location is 38 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 http://www.swift.ac.uk/sper. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 92 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 the expected extinction corresponding to E(B-V) of
0.08. 

This GRB was also detected by Fermi/GBM (trignum=191031891, GCN
26111
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 ), and the INTEGRAL/SPIACS event (trignum=8402). We note that the
Fermi automated circular has misnamed this event GRB 191031C. 

Burst Advocate for this burst is V. D'Elia (delia AT ssdc.asi.it). 
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/)