Gamma-ray binaries as non-accreting pulsar systems

TL;DR

This paper reviews gamma-ray binaries as potential non-accreting pulsar systems, analyzing multi-frequency observations and models to understand their TeV and GeV emissions and the challenges in detecting pulsar signatures.

Contribution

It provides a comprehensive overview of gamma-ray binaries as non-accreting pulsar systems, discussing observational evidence, models, and the potential for multi-component emission explanations.

Findings

Gamma-ray binaries show correlated TeV and GeV emissions.

Current observations face challenges in detecting pulsar signatures.

A two-component model could explain the observed spectral and orbital variations.

Abstract

The gamma-ray binaries LS 5039 and LS I +61 303 have been detected by Cerenkov telescopes at TeV energies, exhibiting periodic behavior correlated with the orbital period. These gamma-ray binary systems have also been recently detected by the Fermi Gamma-ray Telescope at GeV energies, and combination of GeV and TeV observations are providing both, expected and surprising results. We summarize these results, also considering the multi-frequency scenario, from the perspective of pulsar systems. We discuss similarities and differences of models in which pulsar wind/star wind shocks, or pulsar wind zone processes lead to particles accelerated enough to emit TeV photons. We discuss in detail the caveats of the current observations for detecting either accretion lines or pulsations from these objects. We also comment on the possibility for understanding the GeV to TeV emission from these binaries with a 2-components contribution to their spectrum. We show that it would be possible to accommodate both, normal pulsar emission and GeV / TeV fluxes that vary with orbital phase. We point out several aspects of this idea that are subject to test with data being currently taken.