GCN Circular 19107

D. Malesani (DARK/NBI), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),
N. P. M. Kuin (UCL-MSSL), A. Y. Lien (GSFC/UMBC),
L. M. McCauley (PSU), D. M. Palmer (LANL), T. G. R. Roegiers (PSU) and
B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team:

At 17:34:32 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 160228A (trigger=676595).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 107.322, +26.956 which is 
   RA(J2000)  =  07h 09m 17s
   Dec(J2000) = +26d 57' 23"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows several separated peaks
with a total duration of about 30 sec.  The peak count rate
was ~4200 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 17:35:45.5 UT, 73.1 seconds after
the BAT trigger. Using promptly downlinked data we find a bright, fading,
uncatalogued X-ray source located at RA, Dec 107.31671, 26.93103 which
is equivalent to:
   RA(J2000)  = 07h 09m 16.01s
   Dec(J2000) = +26d 55' 51.7"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 91 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.   

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 9.03
x 10^20 cm^-2 (Willingale et al. 2013). 

The initial flux in the 2.5 s image was 1.37e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of nominal 150.000 seconds with the White
filter starting 83 seconds after the BAT trigger. No credible afterglow
candidate has been found in the initial data products. Data from the 2.7'x2.7'
sub-image are not available at this time. 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 0.06. 

Burst Advocate for this burst is D. Malesani (malesani AT dark-cosmology.dk). 
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.)