GCN Circular 43359

T. M. Parsotan (GSFC), P. A. Evans (U Leicester),
R. Gupta (NASA GSFC), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL),
A. Mei (INAF-OAB), K. L. Page (U Leicester), C. Salvaggio (INAF-OAB)
and B. Sbarufatti (INAF-OAB) report on behalf of the Neil Gehrels
Swift Observatory Team:

At 12:47:15 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 260109C (trigger=1434591).  Swift slewed immediately to the burst.
The BAT on-board calculated location is 
RA, Dec 123.728, -35.258 which is 
   RA(J2000) = 08h 14m 55s
   Dec(J2000) = -35d 15' 27"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of about 15 sec.  The peak count rate
was ~4000 counts/sec (15-350 keV), at ~10 sec after the trigger.

The XRT began observing the field at 12:48:41.8 UT, 86.8 seconds after
the BAT trigger. No source was detected in 1.3 ks of promptly
downlinked data. We are waiting for the full dataset to detect and
localise the XRT counterpart.

UVOT took a finding chart exposure of 250 seconds with the U filter starting
146 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 19.2 mag. The
8'x8' region for the list of sources generated on-board covers 100% of the BAT
error circle. The limiting magnitude for the list of sources is expected to be
about 17.7. No correction has been made for extinction.

Burst Advocate for this burst is T. M. Parsotan (tyler.parsotan AT nasa.gov).
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/)