The TeV emitter structure in LS 5039

TL;DR

This paper investigates the structure and location of TeV gamma-ray emission in LS 5039, considering electromagnetic cascades, jet-like flows, and pulsar scenarios to explain observed high-energy emissions despite gamma-ray absorption.

Contribution

It proposes a detailed analysis of the emission region in LS 5039, exploring scenarios that reconcile gamma-ray detection with absorption effects and observational constraints.

Findings

Electromagnetic cascades are inefficient for typical magnetic fields.

A jet-like flow can transport energy to less opaque regions.

The standard pulsar scenario faces constraints from X-ray observations.

Abstract

LS 5039 is an X-ray binary detected at very high energies. Along the orbit, there is a significant detection even during the superior conjunction of the compact object, when very large gamma-ray opacities are expected. Electromagnetic cascades, which may make the system more transparent to gamma-rays, are hardly efficient for reasonable magnetic fields in the massive star surroundings. A jet-like flow could transport energy to regions where the photon-photon absorption is much lower and the TeV radiation is not so severely absorbed. Otherwise, in the standard pulsar scenario for LS 5039, the emitter would be located between the star and the compact object, which would imply the violation of the observational constraints at X-rays.