GCN Circular 4429

H. Ziaeepour (UCL-MSSL), A. Blustin (UCL-MSSL), D. Burrows (PSU),
J. Cummings (GSFC/ORAU), N. Gehrels (GSFC), O. Godet (U. Leicester),
J. Kennea (PSU), C. Markwardt (GSFC/UMd), K. Page (U. Leicester), and
D. Palmer (LANL)
on behalf of the Swift team:

At 06:49:28 UT, Swift-BAT triggered and located GRB 060105
(trigger=175942).   The spacecraft slewed immediately.  The BAT
on-board  calculated location is RA,Dec 297.474d, +46.362d
{19h 49m 54s, +46d 21' 45"} (J2000), with an  uncertainty of
3 arcmin (radius, 90% containment, stat+sys). The BAT light curve
shows a multi-peaked structure with a total
duration of 60 sec, beginning around T-20s.  The peak count
rate is ~20000 counts/sec (15-350 keV), at ~10 seconds after
the trigger.

XRT began observing the field at 06:50:55.3 UT, 87 sec after the BAT
trigger. Onboard centroiding found a bright fading uncatalogued X-ray
source in the field of view at the following coordinates:
RA(J2000):   19h 50m 01.1s
Dec(J2000):  +46d 21' 01.0"
We estimate the uncertainty of this position to be 7 arcsec (radius,
90% containment).  This uncertainty includes a systematic error of
about 5 arcseconds in the on-board calculated positions due to
the XRT boresight offset. This position is 87 arcsec from the BAT
position above. The initial source flux is 6.8e-9 erg/cm2/sec.
We note that the automated GCN notice identified this as a
probable cosmic ray.  The XRT image at the position given above is
definitely a bright celestial source, not a cosmic ray.

UVOT took a finding chart exposure of 200 seconds with the V filter
starting 91 seconds after the BAT trigger. The 2.7'x2.7' sub-image
covers 100% of the XRT error circle. The 8'x8' region for the list
of sources  generated on-board covers 100% of the XRT error circle.
No unambiguous afterglow  candidate has been found in the initial
data products, although there is a potential  low-significance UVOT
counterpart on the edge of the XRT error circle, at
RA=19h 50m 01s DEC=+46d 20m 56s, with a V magnitude of ~19.
The typical 3-sigma upper limit has been about 18th mag.
No correction has  been  made for the expected visual
extinction of about 0.6 magnitudes. The XRT position is very close
to a bright (B mag ~ 12.8) star.

We are currently in the portion of the orbits where the spacecraft
does  not pass over the Malindi downlink station. Therefore, it will
be ~8 hours before we have access to the full data set for the
refined analyses.