GCN Circular 18912

L. M. Z. Hagen (PSU), D. N. Burrows (PSU), P.A. Evans (U Leicester),
J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA),
F. E. Marshall (NASA/GSFC), L. M. McCauley (PSU),
K. L. Page (U Leicester) and B. Sbarufatti (INAF-OAB/PSU) report on
behalf of the Swift Team:

At 13:50:37 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 160121A (trigger=671231).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 109.079, -23.578 which is 
   RA(J2000) = 07h 16m 19s
   Dec(J2000) = -23d 34' 40"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single FRED-
shaped peak with a duration of about 15 sec.  The peak count rate
was ~1700 counts/sec (15-350 keV), at ~2 sec after the trigger. 

The XRT began observing the field at 13:52:08.7 UT, 91.0 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 109.0890, -23.5920
which is equivalent to:
   RA(J2000)  = 07h 16m 21.35s
   Dec(J2000) = -23d 35' 31.3"
with an uncertainty of 2.4 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 consistent with the Galactic value of 5.26
x 10^21 cm^-2 (Willingale et al. 2013). 

UVOT took a finding chart exposure of nominal 250.000 seconds with the U filter
starting 151 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 18.0 mag. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.66. 

Burst Advocate for this burst is L. M. Z. Hagen (lea.zernow.hagen AT gmail.com). 
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.)