GCN Circular 23648

B. Sbarufatti (PSU), S. D. Barthelmy (GSFC), J.D. Gropp (PSU),
J. A. Kennea (PSU) and K. L. Page (U Leicester) report on behalf of
the Neil Gehrels Swift Observatory Team:

At 11:56:09 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 190109B (trigger=882809).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 55.595, +63.578, which is 
   RA(J2000)  =  03h 42m 23s
   Dec(J2000) = +63d 34' 40"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single peak
with a duration of about 10 sec.  The peak count rate
was ~1700 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 11:57:36.3 UT, 87.1 seconds after
the BAT trigger. No source was detected in the 2.5-s promptly available
image. We are waiting for the full dataset to detect and localise the
XRT counterpart. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 90 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 25% of
the BAT 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
BAT 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
0.70. 

Even without an XRT detection, we believe this event to be a real GRB
given an 8.6 sigma detection in BAT and that there is a temporal coincidence
with a Fermi-GBM event.  However there still is a possibility that this
is not real.  We will have to wait for the full data set to be downlinked. 

Burst Advocate for this burst is B. Sbarufatti (bxs60 AT 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.)