GCN Circular 21976

J. K. Cannizzo (NASA/UMBC), S. D. Barthelmy (GSFC),
J. R. Cummings (NASA/UMBC), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester) and M. H. Siegel (PSU) report on behalf of
the Swift Team:

At 11:57:38 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 171007A (trigger=777215).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 135.544, +42.849, which is 
   RA(J2000)   = 09h 02m 10s
   Dec(J2000) = +42d 50' 57"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows several peaks
with a total duration of about 25 sec.  The peak count rate
was ~2000 counts/sec (15-350 keV), at ~3 sec after the trigger. 

The XRT began observing the field at 11:58:47.2 UT, 68.9 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
135.6006, 42.8195 which is equivalent to:
   RA(J2000)  = 09h 02m 24.15s
   Dec(J2000) = +42d 49' 10.3"
with an uncertainty of 2.3 arcseconds (radius, 90% containment). This
location is 183 arcseconds from the BAT onboard position, at the edge of 
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 2.05
x 10^20 cm^-2 (Willingale et al. 2013). 

The initial flux in the 2.5 s image was 6.22e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 77 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
0.02. 

Burst Advocate for this burst is J. K. Cannizzo (cannizzo AT milkyway.gsfc.nasa.gov). 
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.)