The origin of the early time optical emission of Swift GRB 080310

TL;DR

This study analyzes multi-wavelength data of GRB 080310, revealing the necessity of a spectral break and the complex interplay between prompt and afterglow emissions in early optical and IR observations.

Contribution

It introduces a model incorporating independent spectral indices for each pulse, improving the understanding of early optical emission in GRB 080310.

Findings

Spectral break needed between optical and 0.3 keV to match fluxes.

Prompt emission dominates early optical and IR in the model.

Both models suggest some pulses have self-absorbed low energy spectra.

Abstract

We present broadband multi-wavelength observations of GRB 080310 at redshift z = 2.43. This burst was bright and long-lived, and unusual in having extensive optical and near IR follow-up during the prompt phase. Using these data we attempt to simultaneously model the gamma-ray, X-ray, optical and IR emission using a series of prompt pulses and an afterglow component. Initial attempts to extrapolate the high energy model directly to lower energies for each pulse reveal that a spectral break is required between the optical regime and 0.3 keV to avoid over predicting the optical flux. We demonstrate that afterglow emission alone is insufficient to describe all morphology seen in the optical and IR data. Allowing the prompt component to dominate the early-time optical and IR and permitting each pulse to have an independent low energy spectral indices we produce an alternative scenario which better describes the optical light curve. This, however, does not describe the spectral shape of GRB 080310 at early times. The fit statistics for the prompt and afterglow dominated models are nearly identical making it difficult to favour either. However one enduring result is that both models require a low energy spectral index consistent with self absorption for at least some of the pulses identified in the high energy emission model.