Modulation Mechanism of TeV, GeV, and X-ray Emission in LS5039

TL;DR

This study models the gamma-ray, GeV, and X-ray emissions in LS5039, explaining observed flux correlations and anticorrelations through anisotropic inverse Compton scattering and gamma-ray absorption, suggesting the compact object is a black hole.

Contribution

The paper introduces a Monte Carlo simulation incorporating electromagnetic cascades to reproduce observed multi-band emissions and flux variations in LS5039, providing new insights into emission mechanisms.

Findings

TeV-GeV anticorrelation explained by anisotropic IC scattering and gamma-ray absorption.

TeV-X-ray correlation due to IC cooling time dependence on orbital phase.

Constraints on inclination angle suggest the compact object is a black hole.

Abstract

The emission mechanism of the gamma-ray binary LS5039 in energy bands of TeV, GeV, and X-ray is investigated. Observed light curves in LS5039 show that TeV and GeV fluxes anticorrelate and TeV and X-ray fluxes correlate. However, such correlated variations have not been explained yet reasonably at this stage. Assuming that relativistic electrons are injected constantly at the location of the compact object as a point source, and that they lose energy only by the inverse Compton (IC) process, we calculate gamma-ray spectra and light curves by the Monte Carlo method, including the full electromagnetic cascade process. Moreover, we calculated X-ray spectra and light curves by using the resultant electron distribution. As a result, we are able to reproduce qualitatively spectra and light curves observed by HESS, Fermi, and Suzaku for the inclination angle i = 30 dig and the index of injected electron distribution p = 2.5. We conclude that TeV-GeV anticorrelation is due to anisotropic IC scattering and anisotropic gamma-gamma absorption, and that TeV-X correlation is due to the dependence of IC cooling time on orbital phases. In addition, the constraint on the inclination angle implies that the compact object in LS5039 is a black hole.