GCN Circular 6002

GRB 070107: Possible UVOT Afterglow

P. T. Boyd (GSFC), M. Chester (PSU), C. B. Markwardt (CRESST/GSFC/USRA)
and F. E. Marshall (GSFC) report on behalf of the Swift team:

In response to GRB 070107 (Stamatikos et al. GCN Circ. 5999
Not found
 
 
)
UVOT took a 100-s finding chart exposure with the White filter (160-650 nm)
starting 183 seconds after the BAT trigger, followed by a 400-s V
finding chart exposure. A second set of finding chart
exposures was obtained starting 868s post-trigger. We detect a
new variable source inside the XRT error region (Kennea et al. 
GCN Circ. 6000
Not found
 
 
) in the first exposure at

  RA(J2000)  =  10 37 36.35
  DEC(J2000) = -53 12 47.5

with a 1-sigma error radius of about 1 arcsec. However, we caution
that this source is in a crowded region at low galactic latitude, 
and only 4.1 arcsec from a bright V=15.9 cataloged star, which
causes the afterglow and the star to be blended in the UVOT image,
and complicates the position, magnitude, and significance estimates.
We estimate a White magnitude of ~19.5 for the new source. The source
is detected at a ~4-sigma significance level. The same source is
detected at a level of 2.7 sigma in the subsequent 400-s V finding chart. 
The new source is not significant in later White and V exposures.

We note that the extinction estimate in this region (whose galactic 
latitude is 4.56 degrees) is large, and uncertain.