[vsnet-grb-info 17508] GRB 160127A: Swift detection of a burst with an optical counterpart

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18938
SUBJECT: GRB 160127A: Swift detection of a burst with an optical counterpart
DATE:    16/01/27 09:05:29 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

A. Amaral-Rogers (U Leicester), A. P. Beardmore (U Leicester),
P.A. Evans (U Leicester), A. Y. Lien (GSFC/UMBC),
P. T. O'Brien (U Leicester), K. L. Page (U Leicester) and
D. M. Palmer (LANL) report on behalf of the Swift Team:

At 08:43:07 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 160127A (trigger=671828).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 225.956, +0.089 which is 
   RA(J2000) = 15h 03m 49s
   Dec(J2000) = +00d 05' 20"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multiple-peaked
structure with a duration of about 20 sec.  The peak count rate
was ~800 counts/sec (15-350 keV), at ~3 sec after the trigger. 

The XRT began observing the field at 08:44:25.9 UT, 78.6 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 225.98136, 0.07222 which is equivalent
to:
   RA(J2000)  = 15h 03m 55.53s
   Dec(J2000) = +00d 04' 20.0"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 109 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 consistent with the Galactic value of 5.71
x 10^20 cm^-2 (Willingale et al. 2013). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 81 seconds after the BAT trigger. There is a candidate afterglow in
the list of sources generated on-board at
  RA(J2000)  =	15:03:55.70 = 225.98209
  DEC(J2000) = +00:04:23.0  =	0.07305
with a 90%-confidence error radius of about 1.10 arc sec. This position is 3.9
arc sec. from the center of the XRT error circle. The estimated magnitude is
18.13. No correction has been made for the expected extinction corresponding to
E(B-V) of 0.06. 

Burst Advocate for this burst is A. Amaral-Rogers (aar14 AT le.ac.uk). 
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.)