GCN Circular 2904

GRB 041218: Optical observations

Klotz, A., Boer M. (OHP), Atteia, J.L., and G. Stratta (LATT) report:

The field of GRB 041218 (Mereghetti, et al., GCNC 2858) was observed with
the TAROT 25 cm robotic telescope at Calern, France.
The unfiltered observations started at 2004 December 18 17:12 UT (beginning
of the night). Due to a technical problem images were slightly defocused.

We co-added 129 frames of 30s from 17:12 to 18:50 UT.
The associated OT described by Torii (GCNC 2860) is detected 0.5 mag fainter
than the nearby star USNO-B1 1613-0027278.
Hence, we estimate its magnitude, R = 19.4 +/- 0.2.

We analyzed the 2MASS catalogue to extract the galactic extinction through
the line of sight of GRB041218. We used the method described in Klotz et al.
(A&A 2004, vol 425, p427). From Earth to a distance modulus of about 8, the
visual extinction is Av=1.45. The 2MASS data doesn't allow probing farer
distances.

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