The TAROT telescopes (Télescopes à Action Rapide pour les Objets Transitoires) are two robotic observatories designed to observe the prompt optical emission counterpart and the early afterglow of gamma ray bursts (GRBs). We present data acquired between 2001 and 2008 and discuss the properties of the optical emission of GRBs, noting various interesting results. The optical emission observed dur...

Postburst evolution of adiabatic fireballs that produce γ-ray bursts is studied. Emphasis has been put on the transition from the highly relativistic phase to the non-relativistic phase, which, according to our calculation, should happen much earlier than previously expected. The theoretical light curves decline a little sharper at the nonrelativistic stage than at early times, but still can fi...

We report on a complete set of early optical afterglows of gamma-ray bursts (GRBs) obtained with the ROTSE-III telescope network from March 2005 through June 2007. This set is comprised of 12 afterglows with early optical and Swift/XRT observations, with a median ROTSE-III response time of 45 s after the start of γ-ray emission (8 s after the GCN notice time). These afterglows span four orders ...

The CCD magnitudes in Cousins R and I photometric passbands are determined for GRB 991216 and GRB 991208 afterglows respectively ∼ 1 and ∼ 3 day after trigger of the corresponding γ−ray bursts. Light curves of the afterglow emissions are obtained by combining the published data with the present measurements in R and I passbands for GRB 991208 and in R, Gunn i and J passbands for GRB 991216. The...

We present photometric multiband spectral energy distributions for the GRB host galaxies: GRB 971214, GRB 970508, GRB 980613, GRB 980703 and GRB 990123 obtained with the 6-m telescope of SAO RAS. Using SEDs for the starburst galaxies, we made estimates of K-correction values and estimated the absolute magnitudes of the GRB host galaxies within the range of cosmological parameters. The compariso...

Context. Before the launch of the Swift satellite, the majority of the gamma-ray burst (GRB) afterglows for which Lyα was redshifted into the observable spectrum showed evidence for a damped Lyα absorber. This small sample indicated that GRBs explode either in galaxies, or regions within them, having high neutral hydrogen column densities. Aims. To increase the spectroscopic sample of GRBs with...

Although observations of circumstellar shock interactions around supernovae are generally consistent with a ρ ∝ r wind surrounding the progenitor star, this is not true for GRB (gamma-ray burst) afterglows. However, GRB 991208 and GRB 000301C may be consistent with wind interaction if the injection particle spectrum is a broken power law. Circumstellar dust echos can place constraints on supern...