Inverse Compton Emission from Relativistic Jets in Binary Systems

TL;DR

This paper investigates how particle transport influences gamma-ray emission modeling in relativistic jets of binary systems like Cygnus X-3, emphasizing the importance of detailed spectral analysis for understanding emission regions.

Contribution

It demonstrates that particle transport significantly impacts gamma-ray lightcurves and challenges one-zone models in compact binary systems, highlighting the need for detailed spectral studies.

Findings

Particle transport affects GeV lightcurves unless jet speed is below 0.7c.

In extended systems, particle transport's impact is nearly unavoidable.

Gamma-gamma attenuation strongly influences the gamma-ray spectrum above 5 GeV.

Abstract

The gamma-ray emission detected from several microquasars can be produced by relativistic electrons emitting through inverse Compton scattering. In particular, the GeV emission detected from Cygnus X-3, and its orbital phase dependence, strongly suggest that the emitting electrons are accelerated in a relativistic jet, and that the optical companion provides the dominant target. Here, we study the effects related to particle transport in the framework of the relativistic jet scenario. We find that even in the most compact binary systems, with parameters similar to Cygnus X-3, particle transport can have a substantial influence on the GeV lightcurve unless the jet is slow, $\beta < 0.7$. In more extended binary systems, strong impact of particle transport is nearly unavoidable. Thus, even for a very compact system such as Cygnus X-3, particle transport significantly affects the ability of one-zone models to infer the properties of the gamma-ray production site based on the shape on the GeV lightcurve. We conclude that a detailed study of the gamma-ray spectrum can further constrain the structure and other properties of the gamma-ray emitter in Cygnus X-3, although such a study should account for gamma-gamma attenuation, since it may strongly affect the spectrum above $5\rm\,GeV$.