GCN Circular 11754

M. Stamatikos (OSU/NASA/GSFC), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
S. Campana (INAF-OAB), P. A. Evans (U Leicester), J. M. Gelbord (PSU),
C. Guidorzi (U Ferrara), S. T. Holland (CRESST/USRA/GSFC),
E. A. Hoversten (PSU), J. A. Kennea (PSU),
H. A. Krimm (CRESST/GSFC/USRA), N. P. M. Kuin (UCL-MSSL),
F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester),
C. Pagani (U Leicester), K. L. Page (U Leicester),
D. M. Palmer (LANL), J. L. Racusin (NASA/GSFC),
E. Sonbas (GSFC/USRA/Adiyaman Univ.), R. L. C. Starling (U Leicester),
C. A. Swenson (PSU) and E. Troja (NASA/GSFC/ORAU) report on behalf of
the Swift Team:

At 21:25:48 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 110223B (trigger=446677).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 150.276, -68.329 which is 
   RA(J2000) = 10h 01m 06s
   Dec(J2000) = -68d 19' 44"
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 5 sec.  The peak count rate
was ~2000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 21:27:00.0 UT, 72.0 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 150.2339,
-68.3019 which is equivalent to:
   RA(J2000)  = 10h 00m 56.15s
   Dec(J2000) = -68d 18' 06.7"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 112 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 1.29
x 10^21 cm^-2 (Kalberla et al. 2005). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 77 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 none of
the XRT error circle. The coverage of the XRT error circle by the 8'x8' region
for the list of sources generated on-board is uncertain because the large
number of sources filled the available telemetry. No correction has been made
for the expected extinction corresponding to E(B-V) of 0.23. 

Burst Advocate for this burst is M. Stamatikos (Michael.Stamatikos-1 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/too.html.)