GCN Circular 21946

A. Y. Lien (GSFC/UMBC), P. D'Avanzo (INAF-OAB), J.D. Gropp (PSU),
J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL), D. M. Palmer (LANL),
M. H. Siegel (PSU) and A. Tohuvavohu (PSU) report on behalf of the
Swift Team:

At 18:25:40 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 171001A (trigger=775553).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 22.088, -11.893 which is 
   RA(J2000) = 01h 28m 21s
   Dec(J2000) = -11d 53' 35"
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 30 sec.  The peak count rate
was ~900 counts/sec (15-350 keV), at ~20 sec after the trigger. 

The XRT began observing the field at 18:28:53.9 UT, 193.7 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 22.0774, -11.8940 which
is equivalent to:
   RA(J2000)  = 01h 28m 18.59s
   Dec(J2000) = -11d 53' 38.5"
with an uncertainty of 2.2 arcseconds (radius, 90% containment). This
location is 37 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.  We
cannot determine whether the source is fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (3.56 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.9
(+3.76/-3.10) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 197 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
0.03. 

Burst Advocate for this burst is A. Y. Lien (amy.y.lien AT 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.)