The bright optical/NIR afterglow of the faint GRB 080710 – evidence of a jet viewed off-axis*
Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany e-mail: firstname.lastname@example.org
2 Universe Cluster, Technische Universität München, Boltzmannstrasse 2, 85748 Garching, Germany
3 Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
4 European Southern Observatory, 85748 Garching, Germany
5 School of Physics, University College Dublin, Dublin 4, Ireland
6 Center for Astrophysics and Cosmology, University of Iceland, Dunhagi 5, 107 Reykjavík, Iceland
7 Institute of Physics, Eötvös University, Pázmány P. s. 1/A, 1117 Budapest, Hungary
8 Department of Physics and Astronomy, Clemson University, Clemson, SC 29634, USA
Accepted: 21 July 2009
Aims. We investigate the optical/near-infrared light curve of the afterglow of GRB 080710 in the context of rising afterglows.
Methods. Optical and near-infrared photometry was performed using the seven-channel imager GROND and the Tautenburg Schmidt telescope. X-ray data were provided by the X-ray Telescope onboard the Swift satellite. We construct an empirical light curve model using the available broadband data, which is well-sampled in the time and frequency domains.
Results. The optical/NIR light curve of the afterglow of GRB 080710 is dominated by an initial increase in brightness, which smoothly turns over into a shallow power law decay. At around 10 ks post-burst, there is an achromatic break from shallow to steeper decline in the afterglow light curve with a change in the power law index of .
Conclusions. The initially rising achromatic light curve of the afterglow of GRB 080710 can be accounted for with a model of a burst viewed off-axis or a single jet in its pre-deceleration phase and in an on-axis geometry. A unified picture of the afterglow light curve and prompt emission properties can be obtained with an off-axis geometry, suggesting that late and shallow rising optical light curves of GRB afterglows might be produced by geometric effects.
Key words: gamma rays: bursts / techniques: photometric
© ESO, 2009