Gamma-ray emission from binaries in context

TL;DR

This paper reviews the diverse mechanisms and recent discoveries of gamma-ray emission from various binary systems, highlighting their significance in high-energy astrophysics and comparing them with similar astrophysical objects.

Contribution

It provides a comprehensive overview of gamma-ray emission mechanisms in binaries and updates on recent observational discoveries and classifications.

Findings

Multiple binary types emit variable gamma rays.

Discovery of gamma-ray emission from novae was unexpected.

Different systems share similar high-energy processes.

Abstract

More than a dozen binary systems are now established as sources of variable, high energy (HE, 0.1-100 GeV) gamma rays. Five are also established sources of very high energy (VHE, >100 GeV) gamma rays. The mechanisms behind gamma-ray emission in binaries are very diverse. My current understanding is that they divide up into four types of systems: gamma-ray binaries, powered by pulsar rotation; microquasars, powered by accretion onto a black hole or neutron star; novae, powered by thermonuclear runaway on a white dwarf; colliding wind binaries, powered by stellar winds from massive stars. Some of these types had long been suspected to emit gamma rays (microquasars), others have taken the community by surprise (novae). My purpose here is to provide a brief review of the current status of gamma-ray emission from binaries, in the context of related objects where similar mechanisms are at work (pulsar wind nebulae, active galactic nuclei, supernova remnants).