GCN Circular 16904

S. D. Barthelmy (GSFC), M. G. Bernardini (INAF-OAB),
D. N. Burrows (PSU), P. D'Avanzo (INAF-OAB), D. Malesani (DARK/NBI),
V. Mangano (PSU), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL),
P. Romano (INAF-IASFPA), B. Sbarufatti (INAF-OAB/PSU),
M. H. Siegel (PSU) and T. N. Ukwatta (LANL) report on behalf of the
Swift Team:

At 15:04:19 UT, the Swift Burst Alert Telescope (BAT) triggered and
located a transient (trigger=614903).  Swift slewed immediately to the transient. 
The BAT on-board calculated location is 
RA, Dec 268.607, -26.330 which is 
   RA(J2000) = 17h 54m 26s
   Dec(J2000) = -26d 19' 48"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty). This is an image trigger so details of the
lightcurve can not yet be determined. 

The XRT began observing the field at 15:06:31.7 UT, 132.4 seconds after
the BAT trigger. XRT found a bright X-ray source located at RA, Dec
268.6054, -26.3282 which is equivalent to:
   RA(J2000)  = +17h 54m 25.30s
   Dec(J2000) = -26d 19' 41.5"
with an uncertainty of 5.8 arcseconds (radius, 90% containment). This
location is 8.3 arcseconds from the BAT onboard position, within the
BAT error circle. This position is 11.1 arcseconds from that of the 
Supergiant Fast X-ray Transient IGR J17544-2619, which is likely to be 
the transient that triggered the BAT.  No event data are yet available 
to determine the column density using X-ray spectroscopy. 

The initial flux in the 0.1 s image was 2.08e-08 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 168 seconds with the U filter
starting  138 seconds after the BAT trigger. The 2.7'x2.7' sub-image
reveals the known  optical counterpart at a U magnitude of 15.27
approximately 10.6" from the XRT source. No other source is detected
to a typical 3-sigma upper limit of about  19.2 mag.  No correction
has been made for the large, but uncertain extinction expected.