GCN Circular 8764

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

We analyzed images of GRB 090102 detected by SWIFT
(trigger 338895) with the TAROT at the Calern
observatory, France.

In our previous GCN Circ. (9761) we made a mistake
in the celestial coordinates of the optical afterglow.
TAROT position is compatible with UVOT (Mangano et
al. GCNC 8762).

The first image is trailed with a duration of 60.0s
(see the description in Klotz et al., 2006, A&A 451, L39)
and we detect the growth of the optical light curve
that culminates at t0+60s (+/- 3s) with a brightness R=13.4
(i.e. ~40s after the end of the gamma activity).
We calibrated magnitudes in R band using
NOMAD1 1231-0209716 (R=13.31).

After t0+60s, the decay of the afteglow is classic with
a decay of alpha=1.6 +/- 0.2. Hereafter, TAROT Calern
data (tstart and tend are expressed in seconds after
the BAT trigger t0):

tstart tend  R      dR
  40.8  46.8  14.3   0.2
  46.8  52.8  13.6   0.1
  52.8  58.8  13.4   0.1
  58.8  64.8  13.4   0.1
  64.8  70.8  13.5   0.1
  70.8  76.8  13.7   0.1
  76.8  82.8  13.7   0.1
  82.8  88.8  14.0   0.1
  88.8  94.8  14.1   0.1
  94.8 100.8  14.3   0.1
107.6 137.6  14.4   0.2
144.6 174.6  14.9   0.2
181.6 211.6  15.5   0.3

Further observations are in progress