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

Abstract

In this paper we further investigate the relationship, reported by Oates et al., 2012, between the optical/UV afterglow luminosity (measured at restframe 200s) and average afterglow decay rate (measured from restframe 200s 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: $\log {\mathrm{L}}_{\mathrm{O},200\mathrm{s}}$ and $\log {\mathrm{L}}_{\mathrm{X},200\mathrm{s}}$; ${\alpha }_{O,>200\mathrm{s}}$ and ${\alpha }_{X,>200\mathrm{s}}$, consistent with simulations. The model also predicts relationships between $\log {\mathrm{E}}_{\mathrm{iso}}$ and $\log {\mathrm{L}}_{200\mathrm{s}}$, however, while we find such relationships in the observed sample, the slope of the linear regression is shallower than that simulated and inconsistent at $\gtrsim 3\sigma$. Simulations also do not agree with correlations observed between $\log {\mathrm{L}}_{200\mathrm{s}}$ and ${\alpha }_{>200\mathrm{s}}$, or $\log {\mathrm{E}}_{\mathrm{iso}}$ and ${\alpha }_{>200\mathrm{s}}$. 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.

17 pages, 5 figures, accepted for publication in MNRAS

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• A Correlation Between the Intrinsic Brightness and Average Decay Rate of Gamma-ray Burst X-ray Afterglow Light Curves
• Swift/UVOT: 18 Years of Long GRB Discoveries and Advances
• Plasmas in Gamma-Ray Bursts: particle acceleration, magnetic fields, radiative Processes and environments