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GCN Circular 6706

Swift detection of a outburst from SAX J1810.8-2609
2007-08-05T12:11:10Z (17 years ago)
Scott Barthelmy at NASA/GSFC <>
A. M. Parsons (GSFC), S. D. Barthelmy (GSFC), N. Gehrels (NASA/GSFC),
C. Guidorzi (Univ Bicocca&INAF-OAB), H. A. Krimm (GSFC/USRA),
V. La Parola (INAF-IASFPA), V. Mangano (INAF-IASFPA),
C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC),
D. M. Palmer (LANL), P. Romano (Univ. Bicocca & INAF-OAB),
G. Sato (GSFC/ISAS), B. Sbarufatti (INAF-IASFPA),
R. L. C. Starling (U Leicester), E. Troja (INAF-IASFPA),
D. E. Vanden Berk (PSU) and H. Ziaeepour (UCL-MSSL) report on behalf
of the Swift Team:

At 2007-08-05 11:27:26 UT, the Swift Burst Alert Telescope (BAT) 
triggered on a burst source not in its onboard catalog (trigger=287042).  
Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec = 272.651, -26.153 which is 
   RA(J2000)  =  18h 10m 36s
   Dec(J2000) = -26d 09' 10"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  This source location is consistent (1.8 arcmin)
with the known Low Mass X-ray Binary V* V4722 Sgr (=SAX J1810.8-2609). 
The BAT light curve shows a single peak with a duration of roughly 5 sec.  
The peak count rate was ~600 counts/sec (15-350 keV), at ~0 sec after 
the trigger. 

The XRT began observing the field at 11:28:25 UT, 59 seconds after the
BAT trigger. XRT found a bright, variable X-ray source
whose position, determined from downlinked data, 
is RA, Dec 272.68594, -26.15055 which is
   RA(J2000)  =  18h 10m 44.63s
   Dec(J2000) = -26d 09' 02.0"
with an uncertainty of 4.5 arcseconds (radius, 90% containment). 
This location is 112 arcseconds from the BAT on-board position,
within the BAT error circle. The initial flux in the 2.5s image
was 4.9e-09 erg/cm2/s (0.2-10 keV). 
The position is 3.69 arcseconds from the LMXB V* V4722 Sgr. 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 70 seconds after the BAT trigger. 
No afterglow candidate has been found in the initial data products. 
There is a high density of sources in the image.  The extinction
toward the field is high, with E(B-V)=0.95. 

Burst Advocate for this burst is A. M. Parsons (parsons AT 
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:
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