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GCN Circular 5212

Subject
GRB 060604: Swift detection of a burst with possible optical counterpart
Date
2006-06-04T18:46:18Z (18 years ago)
From
Jamie A. Kennea at PSU/Swift-XRT <kennea@astro.psu.edu>
M. J. Page (UCL-MSSL), A. J. Blustin (UCL-MSSL),
J. R. Cummings (NASA/ORAU), N. Gehrels (NASA/GSFC),
O. Godet (U Leicester), J. A. Kennea (PSU), K. M. McLean (LANL/UTD),
K. L. Page (U Leicester), G. Sato (GSFC/JSPS/USRA) and
M. Stamatikos (NASA/ORAU) report on behalf of the Swift Team:

At 18:19:00 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 060604 (trigger=213486).  Swift slewed immediately to the 
burst.  The BAT on-board calculated location is 
RA,Dec 337.242, -10.905 {22h 28m 58s, -10d 54' 17"} (J2000)
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single FRED
peak with a duration of about 8 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~3 sec after the trigger. 

The XRT began observing the field at 18:20:48 UT, 109 seconds after the
BAT trigger. XRT found a variable, uncatalogued X-ray source
located at RA(J2000) = 22h 28m 54.9s, Dec(J2000) = -10d 55' 03.0", with an
estimated uncertainty of 4.7 arcseconds (90% confidence radius). 
During the first 100s of data, the source shows bright flaring activity. 
This location is 65 arcseconds from the BAT on-board position, within
the BAT error circle. The initial flux in the 2.5s image was
2.9e-09 erg/cm2/s (0.2-10 keV). 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 117 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 (337.2292,-10.9155) or
(22h28m55.01s,-10o54'55.8")  with a 1-sigma error radius of about 0.6
arc sec. This position is 7.2 arc sec. from the center of the XRT
error circle. The estimated magnitude is 18.0 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  0.04.
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