Wind-powered afterglows of gamma-ray bursts: flares, plateaus and steep decays

Abstract

Afterglows of gamma-ray bursts often show flares, plateaus, and sudden intensity drops: these temporal features are difficult to explain as coming from the forward shock. We calculate radiative properties of early GRB afterglows with the dominant contribution from the reverse shock (RS) propagating in an ultra-relativistic (pulsarlike) wind produced by the long-lasting central engine. RS emission occurs in the fast cooling regime -this ensures high radiative efficiency and allows fast intensity variations. We demonstrate that: (i) mild wind power, of the order of ∼ 10 46 erg s −1 , can reproduce the afterglows' plateau phase; (ii) termination of the wind can produce sudden steep decays; (iii) mild variations in the wind luminosity can produce short-duration afterglow flares.