GCN Circular 11857

T. N. Ukwatta (MSU), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), N. Gehrels (NASA/GSFC),
J. M. Gelbord (PSU), S. T. Holland (CRESST/USRA/GSFC),
J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA),
C. B. Markwardt (NASA/GSFC), F. E. Marshall (NASA/GSFC),
A. Melandri (INAF-OAB), C. Pagani (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL),
C. J. Saxton (UCL-MSSL), M. C. Stroh (PSU), C. A. Swenson (PSU) and
E. Troja (NASA/GSFC/ORAU) report on behalf of the Swift Team:

At 00:12:57 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 110402A (trigger=450545).  Swift slewed to the burst at T+9 min. 
The BAT on-board calculated location is RA, Dec 197.419, +61.242 which is 
   RA(J2000) = 13h 09m 41s
   Dec(J2000) = +61d 14' 30"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed multiple short spikes
with a total duration of about 40 sec.  The peak count rate
was ~9000 counts/sec (15-350 keV), at ~5 sec after the trigger. 

The XRT began observing the field at 00:22:01.5 UT, 544.3 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 197.4014,
61.2527 which is equivalent to:
   RA(J2000)  = 13h 09m 36.33s
   Dec(J2000) = +61d 15' 09.6"
with an uncertainty of 2.3 arcseconds (radius, 90% containment). This
location is 49 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 consistent with the Galactic value of 1.62
x 10^20 cm^-2 (Kalberla et al. 2005). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 547 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 19.6 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 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.02. 

Burst Advocate for this burst is T. N. Ukwatta (tilan.ukwatta 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.)