The nature of LS 5039 under the scrutiny of gamma-rays

TL;DR

This paper models the high-energy gamma-ray emission of LS 5039 assuming it contains a pulsar, successfully explaining current observations and predicting future detectable signals to determine the system's nature.

Contribution

It provides a detailed theoretical model of LS 5039's gamma-ray phenomenology assuming a pulsar companion, including system geometry and cascading processes, and offers testable predictions for upcoming observations.

Findings

Model reproduces H.E.S.S. spectra and lightcurves

Predicts detectable signals for E>1 GeV with GLAST

Provides future observational tests to identify the system's nature

Abstract

Several gamma-ray binaries have been recently detected by the High-Energy Stereoscopy Array (H.E.S.S.) and the Major Atmospheric Imaging Cerenkov (MAGIC) telescope. In two cases, their nature is unknown, since a final observational feature for a black hole or a pulsar compact object companion is still missing. One such system is LS 5039. Here we present results from a model (it includes a detailed account of the system geometry, the angular dependence of processes such as Klein-Nishina inverse Compton and gamma-gamma absorption, and a Monte Carlo simulation of cascading) of the high energy phenomenology of LS 5039 in which it is assumed that the companion object is a pulsar rotating around an O6.5V star in the 3.9 days orbit. We show that the H.E.S.S. phenomenology at all scales (spectra along the orbit in both broad and short phase-bins and lightcurve) is described within this model. We focus on presenting predictions for photons with lower energies (for E>1 GeV), subject to test in the forthcoming months with the GLAST satellite, and we also present predictions for future observations with high-energy arrays, such as H.E.S.S. II. Both set of predictions go beyond the description of the current data, and could provide a high-energy determination of the system's composition.