Taxonomy of GRB optical light-curves: identification of a salient class of early afterglows

TL;DR

This paper classifies early optical light-curves of Gamma-Ray Burst afterglows into four categories, identifying a new salient class and exploring their physical origins and potential as standard candles.

Contribution

It introduces a taxonomy of GRB optical afterglows, highlighting a new salient class and analyzing their physical mechanisms and correlations.

Findings

Four classes of early optical afterglows identified

Correlations suggest structured outflow seen off-axis for fast-rising afterglows

Potential use of light-curve relations as standard candles

Abstract

The temporal behaviour of the early optical emission from Gamma-Ray Burst afterglows can be divided in four classes: fast-rising with an early peak, slow-rising with a late peak, flat plateaus, and rapid decays since first measurement. The fast-rising optical afterglows display correlations among peak flux, peak epoch, and post-peak power-law decay index that can be explained with a structured outflow seen off-axis, but the shock origin (reverse or forward) of the optical emission cannot be determined. The afterglows with plateaus and slow-rises may be accommodated by the same model, if observer location offsets are larger than for the fast-rising afterglows, or could be due to a long-lived injection of energy and/or ejecta in the blast-wave. If better calibrated with more afterglows, the peak flux-peak epoch relation exhibited by the fast and slow-rising optical light-curves could provide a way to use this type of afterglows as standard candles.