Gamma‐Ray Burst afterglows: theory and observations

Abstract

I discuss some theoretical expectations for the synchrotron emission from a relativistic blast‐wave interacting with the ambient medium, as a model for GRB afterglows, and compare them with observations. An afterglow flux evolving as a power‐law in time, a bright optical flash during and after the burst, and light‐curve breaks owing to a tight ejecta collimation are the major predictions that were confirmed observationally, but it should be recognized that light‐curve decay indices are not correlated with the spectral slopes (as would be expected), optical flashes are quite rare, and jet‐breaks harder to find in Swift X‐ray afterglows.X‐ray light‐curve plateaus could be due to variations in the average energy‐per‐solid‐angle of the blast‐wave, confirming to two other anticipated features of GRB outflows: energy injection and angular structure. The latter is also the more likely origin of the fast‐rises seen in some optical light‐curves. To account for the existence of both chromatic and achromatic aftergl...