GRB 091029: At the limit of the fireball scenario

TL;DR

This study analyzes the complex afterglow of GRB 091029 using multi-wavelength data, proposing a two-component outflow model to explain decoupled light curves, but the model's numerous unknowns hinder definitive conclusions.

Contribution

It introduces a two-component outflow model to explain decoupled light curves in GRB 091029's afterglow, challenging the simplicity of the standard fireball scenario.

Findings

Two-component outflow explains decoupled light curves

Standard fireball model insufficient for this GRB

Model complexity limits definitive validation

Abstract

Using high-quality, broad-band afterglow data for GRB 091029, we test the validity of the forward-shock model for gamma-ray burst afterglows. We used multi-wavelength (NIR to X-ray) follow-up observations obtained with the GROND, BOOTES-3/YA and Stardome optical ground-based telescopes, and the UVOT and the XRT onboard the Swift satellite. To explain the almost totally decoupled light curves in the X-ray and optical/NIR domains, a two-component outflow is proposed. Several models are tested, including continuous energy injection, components with different electron energy indices and components in two different stages of spectral evolution. Only the last model can explain both the decoupled light curves with asynchronous peaks and the peculiar SED evolution. However, this model has so many unknown free parameters that we are unable to reliably confirm or disprove its validity, making the afterglow of GRB 091029 difficult to explain in the framework of the simplest fireball model.