TITLE:   GCN CIRCULAR
NUMBER:  20618
SUBJECT: GRB 170206B: Swift detection of a burst
DATE:    17/02/06 22:29:11 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@milkyway.gsfc.nasa.gov>

A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC),
A. Cholden-Brown (PSU), J. A. Kennea (PSU),
F. E. Marshall (NASA/GSFC), B. Mingo (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL), P. Romano (INAF-OAB),
B. Sbarufatti (INAF-OAB/PSU) and E. Troja (NASA/GSFC/UMCP) report on
behalf of the Swift Team:

At 21:57:25 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 170206B (trigger=737125).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 271.786, +11.223, which is 
  RA(J2000) = 18h 07m 09s
  Dec(J2000) = +11d 13' 23"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  Due to a processing outage, the real-time light curve
is not available at this time. 

Using promptly downlinked data we find an uncatalogued X-ray source
with an enhanced position: RA, Dec 271.7708, 11.1943 which is
equivalent to:
   RA(J2000)  = 18h 07m 04.98s
   Dec(J2000) = +11d 11' 39.4"
with an uncertainty of 2.2 arcseconds (radius, 90% containment). 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 in excess of the Galactic value (1.13 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 2.8
(+2.82/-2.42) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 250 seconds with the U filter. 
No credible afterglow candidate has been found in the initial data products. 
The 2.7'x2.7' sub-image covers none of the
XRT error circle. 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 of E(B-V) = 0.146. 

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.)