GRB 081029: Understanding Multiple Afterglow Components

Abstract

We present an analysis of the unusual optical light curve of the gamma-ray burst GRB 081029, which occurred at a redshift of z = 3.8479. We combine X-ray and optical observations from the Swift X-Ray Telescope and the Swift UltraViolet Optical Telescope with optical and infrared data obtained using the REM and ROTSE telescopes to construct a detailed data set extending from 86 s to similar to 100 000 s after the BAT trigger. Our data also cover a wide energy range, from 10 keV to 0.77 eV (1.24 angstrom to 16 000 angstrom). The X-ray afterglow shows a shallow initial decay followed by a rapid decay starting at about 18 000 s. The optical and infrared afterglow, however, shows an uncharacteristic rise at about 5000 s that does not correspond to any feature in the X-ray light curve. Our data are not consistent with synchrotron radiation from a single-component jet interacting with an external medium. We do, however, find that the observed light curve can be explained using multi-component model for the jet.