TITLE:   GCN CIRCULAR
NUMBER:  28666
SUBJECT: GRB 201017A: Swift detection of a burst
DATE:    20/10/17 10:03:23 GMT
FROM:    Boris Sbarufatti at PSU  <bxs60@psu.edu>

A. D'Ai (INAF-IASFPA), E. Ambrosi (INAF-IASFPA), V. D'Elia (SSDC),
J.D. Gropp (PSU), N. J. Klingler (PSU), A. Y. Lien (GSFC/UMBC),
F. E. Marshall (NASA/GSFC), T. Sakamoto (AGU) and B. Sbarufatti (PSU)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 09:46:31 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 201017A (trigger=1000613).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 36.633, +66.673 which is 
   RA(J2000) = 02h 26m 32s
   Dec(J2000) = +66d 40' 22"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of at least 10 sec. Data from ~T+10 s to
~T+100 s are currently unavailable. There might be additional 
burst emission during this interval. The peak count rate
was ~1000 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 09:48:15.1 UT, 103.8 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 36.6186,
66.6787 which is equivalent to:
   RA(J2000)  = 02h 26m 28.45s
   Dec(J2000) = +66d 40' 43.4"
with an uncertainty of 2.4 arcseconds (radius, 90% containment). This
location is 29 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 5.70
x 10^21 cm^-2 (Willingale et al. 2013). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 106 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
1.20. 

Burst Advocate for this burst is A. D'Ai (antonino.dai AT inaf.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/)