GCN Circular 6332

Klotz, A. (CESR-OMP), Boer M. (OHP), Atteia J.L. (LATT-OMP) report:

We imaged the field of GRB 070420 detected by SWIFT
(trigger 276321) with the TAROT robotic telescope (D=25cm)
located at the European Southern Observatory,
La Silla observatory, Chile.

The observations started 34s after the GRB trigger
(8s after the notice) when the GRB was still active.
The elevation of the field decreased from
from 7 degrees above horizon and weather conditions
were good but with some thin clouds in the sky.

The date of trigger : t0 = 2007-04-20T06:18:13.824

The first image is trailed with a duration of 60.0s
(see the description in Klotz et al., 2006, A&A 451, L39).
We do not detect the OT mentioned by Stamatikos et
al. (GCNC 6330) with a limiting magnitude of:
t0+34s to t0+94s : R > 16.1

The second image is 30.0s exposure in tracking mode.
We detect the OT:
t0+100s to t0+130s : R = 16.2

The third image is 30.0s exposure in tracking mode:
t0+136s to t0+166s : R = 16.4

Magnitudes were estimated with the nearby USNO-B1 stars
and are not corrected for galactic dust extinction.

It seems that this afterglow is very red compared to
values published by Stamatikos et al. (GCNC 6330)
and by D'Avanzo et al. GCNC 6331).

N.B. Galactic coordinates are lon=260.8667 lat= -7.4088
and the galactic extinction in R band is 0.7 magnitudes
estimated from D. Schlegel et al. 1998ApJ...500..525S.

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