GLAST testing of a pulsar model matching H.E.S.S. observations of LS 5039

TL;DR

This paper models the gamma-ray emission of LS 5039 assuming a pulsar companion, successfully explaining H.E.S.S. observations and predicting testable signals for the GLAST satellite to validate the pulsar hypothesis.

Contribution

The study introduces a pulsar-based model for LS 5039's high-energy emission that matches H.E.S.S. data and provides predictions for future GLAST observations.

Findings

H.E.S.S. phenomenology is fully explained by the pulsar model.

The model predicts detectable signals for GLAST within one year.

Different spectral parameters are associated with orbital phases.

Abstract

LS 5039 is one of a handful of X-ray binaries that have been recently detected at high-energy $\gamma$-rays, in this case, by the High-Energy Stereoscopy Array (H.E.S.S.). The nature of this system is unknown: both a black hole and a pulsar have been invoked as possible compact object companions. Here we work with a model of the high energy phenomenology of the system in which it is assumed that the companion object is a pulsar rotating around an O6.5V star in the $\sim 3.9$ days orbit. The model assumes two different sets of power-law spectral parameters of the interacting primary leptons corresponding to the two orbital phase intervals defined by H.E.S.S. as having different gamma-ray spectra and very-high-energy (VHE) cutoffs. We show the H.E.S.S. phenomenology is completely explained by this model. We present predictions for photons with lower energies (for $E>1 $ GeV), subject to test in the forthcoming months with the GLAST satellite. We find that GLAST is able to judge on this model within one year.