TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  2829
SUBJECT: GRB041006, late-time optical photometry
DATE:    04/11/04 03:51:19 GMT
FROM:    Peter Garnavich at U of Notre Dame  <pgarnavi@nd.edu>

A. Garg, C. Stubbs, P. Challis, K. Z. Stanek (CfA), and
       P. Garnavich (Notre Dame)

We imaged the field of the GRB 041006 afterglow (Da Costa, Noel,
& Price, GCN 2765) with the 6.5m Clay telescope of the Magellan
Observatory on Nov. 3.1 (UT). A total exposure of 900s in
the R filter was obtained with the MagIC instant imager in
0.6 arcsec seeing. We compared the Magellan image to data taken with
the Vatican Advanced Technology Telescope (VATT) less than 2 days
after the burst (GCN 2792) and detect a source at the
position of the afterglow. Assuming the star 9" west and 4" north
of the afterglow has a brightness of R=21.9 mag (based on the VATT
calibration), we estimate the source in the Magellan images
to be R=24.4 +/- 0.2 mag.

This is approximately 2 mags brighter than the extrapolation of
first 4 days of the afterglow light curve. It is also marginally
fainter than the brightness estimate of Bikmaev et al. (GCN 2826)
on Oct. 18, implying that the source is variable and is not a structure
on the host galaxy. We conclude that the light is dominated by
a supernova that reached its peak brightness in the past two weeks.

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