[vsnet-grb-info 17497] GRB 160123A: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18926
SUBJECT: GRB 160123A: Swift detection of a burst
DATE:    16/01/23 09:18:57 GMT
FROM:    Boris Sbarufatti at INAF-OAB/IASFPA  <boris.sbarufatti at brera.inaf.it>

D. Malesani (DARK/NBI), S. D. Barthelmy (GSFC), T. Sakamoto (AGU) and
B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team:

At 08:58:20 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 160123A (trigger=671447).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 150.286, -33.779 which is 
   RA(J2000) = 10h 01m 09s
   Dec(J2000) = -33d 46' 43"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a double-peaked 
structure with a duration of about 25 sec.  The peak count rate
was ~1500 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 08:59:38.1 UT, 78.0 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 150.3125, -33.7754
which is equivalent to:
   RA(J2000)  = 10h 01m 14.99s
   Dec(J2000) = -33d 46' 31.3"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 80 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 in excess of the Galactic value (1.31 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 2.9
(+2.66/-2.30) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 250 seconds with the U filter starting
295 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 19.2 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 18.0 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.10. 

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.)