Nonrelativistic phase in gamma-ray burst afterglows

TL;DR

This paper reviews gamma-ray burst afterglows, emphasizing the significance of the nonrelativistic phase, introduces a unified dynamical model for all phases, and discusses the deep Newtonian phase's role in afterglow evolution.

Contribution

It presents a generic dynamical model applicable to both relativistic and nonrelativistic phases of gamma-ray burst afterglows, including the deep Newtonian phase.

Findings

Unified model for afterglow evolution from early to late stages

Highlighting the importance of the nonrelativistic phase

Introduction of the deep Newtonian phase concept

Abstract

The discovery of multiband afterglows definitely shows that most $\gamma$-ray bursts are of cosmological origin. $\gamma$-ray bursts are found to be one of the most violent explosive phenomena in the Universe, in which astonishing ultra-relativistic motions are involved. In this article, the multiband observational characteristics of $\gamma$-ray bursts and their afterglows are briefly reviewed. The standard model of $\gamma$-ray bursts, i.e. the fireball model, is described. Emphasis is then put on the importance of the nonrelativistic phase of afterglows. The concept of deep Newtonian phase is elaborated. A generic dynamical model that is applicable in both the relativistic and nonrelativistic phases is introduced. Based on these elaborations, the overall afterglow behaviors, from the very early stages to the very late stages, can be conveniently calculated.