GCN Circular 10336

M. De Pasquale (UCL-MSSL), S. D. Barthelmy (GSFC),
D. N. Burrows (PSU), S. Campana (INAF-OAB), P.A. Curran (MSSL-UCL),  
N. Gehrels (NASA/GSFC), S. T. Holland (CRESST/USRA/GSFC),
J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA),
V. Mangano (INAF-IASFPA), R. Margutti (Univ Bicocca&OAB),
C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC),
C. Pagani (PSU), D. M. Palmer (LANL), P. Romano (INAF-IASFPA),
T. Sakamoto (NASA/UMBC), B. Sbarufatti (INAF-OAB/IASFPA),
M. H. Siegel (PSU), M. Stamatikos (OSU/NASA/GSFC) and
T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team:

At 21:06:19 UT, the Swift Burst Alert Telescope (BAT) triggered and  
located GRB 100117A (trigger=382941).  Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 11.260, -1.594 which is
   RA(J2000)  =  00h 45m 02s
   Dec(J2000) = -01d 35' 38"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty).  The BAT light curve shows a single spike   
structure with a duration of about 0.4 sec.  The peak count rate
was ~4500 counts/sec (15-350 keV), at T_zero.

The XRT began observing the field at 21:07:39.6 UT, 80.1 seconds after   
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 11.26946, -1.59620 which
is equivalent to:
   RA(J2000)  = 00h 45m 4.67s
   Dec(J2000) = -01d 35' 46.3"
with an uncertainty of 4.6 arcseconds (radius, 90% containment). This
location is 34 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 in excess of the Galactic value (2.66e+20
cm^-2, Kalberla et al. 2005), with an excess column of 4 (+3.65/-2.58)
x 10^21 cm^-2 (90% confidence).

The initial flux in the 2.5 s image was 1.24e-09 erg cm^-2 s^-1 (0.2-10
keV).


UVOT took a finding chart exposure of 150 seconds with the White filter
starting 88 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 M. De Pasquale (mdp AT mssl.ucl.ac.uk).
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.)