TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  5260
SUBJECT: GRB 060605, optical observations
DATE:    06/06/15 15:55:39 GMT
FROM:    Peter Garnavich at U of Notre Dame  <pgarnavi@nd.edu>

Agata Karska and Peter Garnavich (Notre Dame)

We observed the position of GRB 060605 (Rykoff et al., GCN 5220)
with the Vatican Advanced Technology Telescope (VATT) and 2KCCD
camera on 2006 June 6.44 UT (16.3 hours after the burst).
Three R-band images, each with an exposure time of 300s, were
combined and a source detected at the Swift/UVOT position
(Page et al., GCN 5221).

Using an average of five USNO-B1.0 stars (magR1) to set the
zero-point we estimate the brightness of the afterglow at
R=21.5 +/- 0.2 mag.

We note that the USNO-B1.0 magR2 values for the star used
by Khamitov et al. (GCN 5224, 5235) and for other stars in the field
provide an inconsistent zero-point with variations of 0.6 mag
when compared to the instrumental magnitudes of our R-band image.
However, the magR1 estimates for the five star are consistent
to 0.1 mag.

Assuming the same calibration as Khamitov et al. (shifting our
GRB magnitude fainter by 0.7 mag) provides a power law decay index
of 2.1 between 6 and 16 hours after the burst. Adding the Khamitov et al.
observation 31 hours after the burst significantly decreases the
decay slope and may indicate contamination from the host galaxy.

This burst was observed by the Spitzer Space Telescope and any additional
photometry would be useful in interpreting the infrared data.

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