TITLE:   GCN CIRCULAR
NUMBER:  19075
SUBJECT: GRB 160225A: Swift detection of a burst
DATE:    16/02/25 14:42:58 GMT
FROM:    David Palmer at LANL  <palmer@lanl.gov>

M. H. Siegel (PSU), A. P. Beardmore (U Leicester),
P.A. Evans (U Leicester), N. Gehrels (NASA/GSFC), J. A. Kennea (PSU),
N. P. M. Kuin (UCL-MSSL), L. M. McCauley (PSU),
K. L. Page (U Leicester), D. M. Palmer (LANL),
T. G. R. Roegiers (PSU), T. Sakamoto (AGU),
B. Sbarufatti (INAF-OAB/PSU) and T. N. Ukwatta (LANL) report on behalf
of the Swift Team:

At 14:20:56 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 160225A (trigger=675998).  Swift's slew was briefly
delayed due to an observing constraint. 
The BAT on-board calculated location is 
RA, Dec 164.242, +53.655 which is 
  RA(J2000) = 10h 56m 58s
  Dec(J2000) = +53d 39' 19"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed multiple spikes
over a 50 second interval.  The peak count rate
was ~1500 counts/sec (15-350 keV) at ~3 sec after the trigger. 

The XRT began observing the field at 14:34:50.6 UT, 834.2 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 164.22846, 53.66991 which is equivalent
to:
   RA(J2000)  = 10h 56m 54.83s
   Dec(J2000) = +53d 40' 11.7"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 60 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 (9.69 x
10^19 cm^-2, Willingale et al. 2013), with an excess column of 3.8
(+4.26/-3.38) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 839 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
0.01. 

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.)