GCN Circular 5044

D. B. Fox (Penn State) and S. B. Cenko (Caltech) report on behalf of a
larger collaboration:

"The robotic Palomar 60-inch telescope (P60) has imaged the
localization region of GRB060501 (Swift trigger 208050; La Parola et
al., GCN 5040
Not found
 
 
) in a series of exposures beginning 08:48 UT (33 minutes
after the burst).  We have compared our i-band images to the
second-epoch digitized sky survey (XDSS) in a search for new sources
consistent with the XRT localization (La Parola et al., GCN 5042
Not found
 
 
).  We
estimate the XDSS limit in this region, by reference to USNO-B1.0
catalog photometry, as I~19.5 mag.  We note that due to the location
of this field close to the Galactic plane, the background stellar
density is large and the estimated Galactic extinction (E_(B-V)~0.3
mag) is substantial.  In particular, there are three star-like objects
in XDSS consistent with the XRT localization.

We find no new i-band sources within or near the XRT localization, to
a limit of I~19 mag in a coaddition of 4x60s images with mean epoch
08:58 UT (43 minutes after the burs).

A deeper coaddition of 5x150s images with mean epoch 09:47 UT (92
minutes after the burst) reveals no new source within the XRT
localization to I~21 mag.  However, we do identify a single new
point-like source with I~19.3 mag, 8.1" from the center of the XRT
localization, at coordinates:

     R.A. 21:53:29.52, Dec. +43:59:49.9 (J2000)

(estimated uncertainty of 0.3" in each coordinate).  There is no
evidence of this source in XDSS survey images.

The source is not resolved from a neighboring star in our earlier
images, which have poorer seeing; however, these images do constrain
the object to not be significantly brighter at 43 minutes post-burst
than at our first detection, 92 minutes post-burst.

Given the absence of evidence for variability, and the distance of the
source from the XRT position, we consider the association of this
source with GRB060501 tentative at this point."