[vsnet-grb-info 3398] GRB 060607: Swift detection of a burst with bright optical counterpart

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  5233
SUBJECT: GRB 060607: Swift detection of a burst with bright optical counterpart
DATE:    06/06/07 05:43:28 GMT
FROM:    Jamie A. Kennea at PSU/Swift-XRT  <kennea at astro.psu.edu>

H. Z. Ziaeepour (UCL-MSSL), S. D. Barthelmy (GSFC),
N. Gehrels (NASA/GSFC), M. R. Goad (U Leicester), J. A. Kennea (PSU),
H. A. Krimm (GSFC/USRA), K. M. McLean (LANL/UTD),
S.R. Oates (UCL-MSSL), K. L. Page (U Leicester) and
M. Stamatikos (NASA/ORAU) report on behalf of the Swift Team:

At 05:12:13 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 060607 (trigger=213823).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA,Dec 329.712, -22.506 {21h 58m 51s, -22d 30' 20"} (J2000)
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a double-peaked
structure with a duration of about 40 sec.  The peak count rate
was ~3000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 05:13:18 UT, 65 seconds after the
BAT trigger. XRT found a bright, variable, uncatalogued X-ray source
located at RA(J2000) = 21h 58m 50.1s, Dec(J2000) = -22d 29' 49.9", with an
estimated uncertainty of 4.7 arcseconds (90% confidence radius). 
This location is 33 arcseconds from the BAT on-board position, within
the BAT error circle. The initial flux in the 2.5s image was
3.3e-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 75 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 (329.7100,-22.4963) or
(21h58m50.40s,-22o29'46.7")  with a 1-sigma error radius of about 0.5
arc sec. This position is 4.7 arc sec. from the center of the XRT
error circle. The estimated magnitude is 15.7 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.