TITLE:   GCN CIRCULAR
NUMBER:  19098
SUBJECT: GRB 160227A: Swift detection of a burst with an optical counterpart
DATE:    16/02/27 19:46:27 GMT
FROM:    David Palmer at LANL  <palmer@lanl.gov>

M. H. Siegel (PSU), D. N. Burrows (PSU), N. Gehrels (NASA/GSFC),
N. P. M. Kuin (UCL-MSSL), A. Y. Lien (GSFC/UMBC),
L. M. McCauley (PSU), D. M. Palmer (LANL),
B. Sbarufatti (INAF-OAB/PSU) and T. N. Ukwatta (LANL) report on behalf
of the Swift Team:

At 19:32:08 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 160227A (trigger=676423).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 194.788, +78.639 which is 
   RA(J2000) = 12h 59m 09s
   Dec(J2000) = +78d 38' 21"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a early complex
structure followed by a stronger peak at around 100 s after the trigger,
for a total duration of at least 160 s.  The peak count rate
was ~700 counts/sec (15-350 keV), at ~100 sec after the trigger. 

The XRT began observing the field at 19:34:39.9 UT, 151.8 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 194.7974, 78.6768 which is equivalent to:
   RA(J2000)  = +12h 59m 11.38s
   Dec(J2000) = +78d 40' 36.5"
with an uncertainty of 5.0 arcseconds (radius, 90% containment). This
location is 136 arcseconds from the BAT onboard position, within the
BAT error circle. No event data are yet available to determine the
column density using X-ray spectroscopy. 

The initial flux in the 2.5 s image was 2.67e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 161 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	12:59:13.84 = 194.80767
  DEC(J2000) = +78:40:44.9  =  78.67913
with a 90%-confidence error radius of about 0.77 arc sec. This position is 11.1
arc sec. from the center of the XRT error circle. The estimated magnitude is
19.32 with a 1-sigma error of about  0.15. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.05. 

Burst Advocate for this burst is M. H. Siegel (siegel AT swift.psu.edu). 
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.)