The unusual X-ray light-curve of GRB 080307: the onset of the afterglow?

TL;DR

This paper analyzes an unusual X-ray light-curve feature in GRB 080307, suggesting it may represent the onset of the afterglow, a rare observation in Swift data, or an alternative flare phenomenon.

Contribution

It introduces a two-component model to interpret the early X-ray emission as the afterglow onset, a rarely observed feature in Swift GRB light-curves.

Findings

The X-ray hump is longer and smoother than typical early flares.

The emission can be modeled as the onset of the afterglow.

Alternative explanations include a slow flare or reverse shock effects.

Abstract

Swift-detected GRB 080307 showed an unusual smooth rise in its X-ray light-curve around 100 seconds after the burst, at the start of which the emission briefly softened. This `hump' has a longer duration than is normal for a flare at early times and does not demonstrate a typical flare profile. Using a two component power-law-to-exponential model, the rising emission can be modelled as the onset of the afterglow, something which is very rarely seen in Swift-X-ray light-curves. We cannot, however, rule out that the hump is a particularly slow early-time flare, or that it is caused by upscattered reverse shock electrons.