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GCN Circular 8524

GRB 081118: Swift detection of a burst
2008-11-18T15:10:34Z (16 years ago)
Scott Barthelmy at NASA/GSFC <>
E. A. Hoversten (PSU), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
M. Capalbi (ASDC), P.A. Curran (MSSL-UCL), M. De Pasquale (UCL-MSSL),
P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC),
O. Godet (U Leicester), D. Grupe (PSU), C. Guidorzi (INAF-OAB),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
V. Mangano (INAF-IASFPA), J. Mao (INAF-OAB),
J. P. Osborne (U Leicester), C. Pagani (PSU), D. M. Palmer (LANL),
J. L. Racusin (PSU), P. Romano (INAF-IASFPA),
B. Sbarufatti (INAF-IASFPA), P. Schady (MSSL-UCL),
R. L. C. Starling (U Leicester), G. Tagliaferri (INAF-OAB),
E. Troja (INAF-IASFPA), T. N. Ukwatta (GSFC/GWU) and L. Vetere (PSU)
report on behalf of the Swift Team:

At 14:56:36 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 081118 (trigger=334877).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 82.590, -43.302 which is 
   RA(J2000)  =  05h 30m 22s
   Dec(J2000) = -43d 18' 07"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  Even though this is an image trigger,
there appears to be a peak of about 600 counts/sec starting 20 to 40 sec
after the start of the trigger integration. 

The XRT began observing the field at 14:59:10.0 UT, 153.3 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 82.59254, -43.30058 which
is equivalent to:
   RA(J2000)  = 05h 30m 22.21s
   Dec(J2000) = -43d 18' 02.1"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 8.4 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 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of
3.74e+20 cm^-2 (Kalberla et al. 2005). 

The initial flux in the 2.5 s image was 6.01e-10 erg cm^-2 s^-1 (0.2-10

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 164 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

Burst Advocate for this burst is E. A. Hoversten (hoversten 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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