GCN Circular 21321

V. D'Elia (ASDC), D. N. Burrows (PSU), A. Cholden-Brown (PSU),
A. D'Ai (INAF-IASFPA), H. A. Krimm (NSF/USRA), D. M. Palmer (LANL) and
B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team:

At 22:20:25 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 170711A (trigger=761622).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 45.786, +47.850 which is 
   RA(J2000) = 03h 03m 09s
   Dec(J2000) = +47d 51' 01"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  Due to a data gap, the BAT light curve is
currently available only until 8 seconds after the trigger. 
The available BAT lightcurve showed a single-peaked
structure with a duration of about 10 sec.  The peak count rate
was ~7000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 22:21:28.7 UT, 63.4 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source located at RA, Dec 45.79854, 47.84896 which
is equivalent to:
   RA(J2000)  = 03h 03m 11.65s
   Dec(J2000) = +47d 50' 56.3"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 30 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 3.23
x 10^21 cm^-2 (Willingale et al. 2013). 

UVOT took a finding chart exposure of 250 seconds with the U filter starting
123 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 19.2 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 18.0 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.31. 

Burst Advocate for this burst is V. D'Elia (delia AT asdc.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/too.html.)