* Astronomy

Title: GRB 081029: A Gamma-Ray Burst with a Multi-Component Afterglow
Authors: Stephen T. Holland, Massimiliano De Pasquale, Jirong Mao, Takanori Sakamoto, Patricia Schady, Stefano Covino, Yi-Zhong Fan, Zhi Ping Jin, Paolo D'Avanzo, Angelo Antonelli, Valerio D'Elia, Guido Chincarini, Fabrizio Fiore, Shashi Bhushan Pandey, Bethany E. Cobb

We present an analysis of the unusual optical light curve of the gamma-ray burst GRB 081029, a long-soft burst with 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 ground-based optical and infrared data obtained using the REM, ROTSE, and CTIO 1.3-m telescopes to construct a detailed data set extending from 86 s to approximately 100,000 s after the BAT trigger. Our data cover a wide energy range, from 10 keV to 0.77 eV (1.24 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 3000 s that does not correspond to any feature in the X-ray light curve. Our data are not consistent with synchrotron radiation from a jet interacting with an external medium, a two-component jet, or continuous energy injection from the central engine. We find that the optical light curves can be broadly explained by a collision between two ejecta shells within a two-component jet. A growing number of gamma-ray burst afterglows are consistent with complex jets, which suggests that some (or all) gamma-ray burst jets are complex and will require detailed modelling to fully understand them.

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