Exploring the canonical behaviour of long gamma-ray bursts using an intrinsic multiwavelength afterglow correlation

Abstract

In this paper, we further investigate the relationship, reported by Oates et al., between the optical/UV afterglow luminosity (measured at restframe 200 s) and average afterglow decay rate (measured from restframe 200 s onwards) of long duration gamma-ray bursts (GRBs). We extend the analysis by examining the X-ray light curves, finding a consistent correlation. We therefore explore how the parameters of these correlations relate to the prompt emission phase and, using a Monte Carlo simulation, explore whether these correlations are consistent with predictions of the standard afterglow model. We find significant correlations between: log L-O,L- 200 s and log L-X,L- 200 (s); alpha(O,> 200) (s) and alpha(X,> 200) (s), consistent with simulations. The model also predicts relationships between log E-iso and log L-200 (s); however, while we find such relationships in the observed sample, the slope of the linear regression is shallower than that simulated and inconsistent at greater than or similar to 3 sigma. Simulations also do not agree with correlations observed between log L-200 (s) and alpha(>200) (s), or log E-iso and alpha(>200) (s). Overall, these observed correlations are consistent with a common underlying physical mechanism producing GRBs and their afterglows regardless of their detailed temporal behaviour. However, a basic afterglow model has difficulty explaining all the observed correlations. This leads us to briefly discuss alternative more complex models.