New orbital solution for LS 5039 and search for period variability

Abstract

In recent decades, the study of high-energy gamma-ray emitting astrophysical objects has led to the discovery of a new type of object called gamma-ray emitting binaries (GREB). Among the approximately 30 known GREBs, several consist of a compact object and a massive star. The ones characterised by having the peak of their spectral energy distribution at >∼ 1 MeV are called gamma-ray binaries (γBs). So far, ten γBs, including LS 5039, have been confirmed as sources of high and/or very high-energy γ-ray emission. Understanding the physical processes of binary systems like LS 5039 is crucial. As their behaviour depends on the orbital phase, obtaining comprehensive information about the orbital parameters and their potential evolution is of great importance. In this work, we report the study of the evolution of the orbital period of LS 5039 through the fitting of orbital solutions to radial velocities using the program Spectroscopy Binary Orbit Program (SBOP). Our study revealed no significant variation within the observed time frame. The new orbital solution we derived, Porb = 3.90599 ± 0.00002 day, is an order of magnitude more precise than the previous solution. Additionally, we assessed the potential impact of energy loss due to the emission of gravitational waves on the orbital period evolution, concluding that it was too small to significantly influence the results