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GCN Circular 5544

GRB 060908: Swift detection of a burst with a bright optical counterpart
2006-09-08T09:16:22Z (18 years ago)
Scott Barthelmy at NASA/GSFC <>
P. A. Evans (U Leicester), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), D. N. Burrows (PSU),
N. Gehrels (NASA/GSFC), O. Godet (U Leicester),
C. Guidorzi (Univ Bicocca&INAF-OAB), J. A. Kennea (PSU),
A. N. Morgan (PSU), K. L. Page (U Leicester), D. M. Palmer (LANL),
P. Romano (INAF-OAB), G. Sato (GSFC/ISAS), M. Stamatikos (NASA/ORAU)
and H. Ziaeepour (UCL-MSSL) report on behalf of the Swift Team:

At 08:57:22 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 060908 (trigger=228581).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA,Dec 31.835, +0.370 {02h 07m 20s, +00d 22' 14"} (J2000)
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows 3 overlapping peaks
starting at ~T-10 sec and then a 4th peak lasting until T+12 sec. 
The peak count rate was ~3000 counts/sec (15-350 keV), at ~T+2 sec
after the trigger. 

The XRT began observing the field at 08:58:34 UT, 72 seconds after the
BAT trigger. XRT found a fading and uncatalogued X-ray source
located at RA(J2000) = 02h 07m 18.1s, Dec(J2000) = +00d 20' 29.1", with an
estimated uncertainty of 3.8 arcseconds (90% confidence radius). 
This location is 108 arcseconds from the BAT on-board position, within
the BAT error circle. The initial flux in the 2.5s image was
5.0e-10 erg/cm2/s (0.2-10 keV). 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 80 seconds after the BAT trigger. There
is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image
at (RA,DEC) (J2000) of (31.8265,0.3420) or (02h07m18.36s,+00o20'31.2")
 with a 1-sigma error radius of about 0.7 arc sec. This position is
3.8 arc sec. from the center of the XRT error circle. The estimated
magnitude is 15.1 with a 1-sigma error of about 0.5 mag. No
correction has been made for the expected extinction corresponding to
E(B-V) of 0.03.
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