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

TL;DR

This paper models gamma-ray burst afterglows considering reverse shock emission in a pulsar-like wind, explaining features like flares, plateaus, and steep decays through wind dynamics.

Contribution

It introduces a model where reverse shock emission in a long-lasting wind explains complex afterglow features not accounted for by forward shock models.

Findings

Mild wind power (~10^{46} erg/s) can produce plateau phases.

Termination of the wind causes steep decays.

Variations in wind luminosity generate short flares.

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 (pulsar-like) 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 $\sim 10^{46}$ 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.