Investigating the Potential of LS 5039 as a Triple System Using Fermi-LAT Data

TL;DR

This study analyzes 16 years of Fermi-LAT data on LS 5039, discovering two new periodic signals that suggest the system may be a triple system with a third body influencing the observed gamma-ray periodicities.

Contribution

The paper provides the first evidence of additional periodic signals in LS 5039, indicating the potential presence of a third body in the system, based on long-term gamma-ray data analysis.

Findings

Discovered two new periodic signals at 3.63819 and 4.21654 days.

Signals suggest possible third body orbiting LS 5039.

Supports the triple system hypothesis through frequency analysis.

Abstract

LS 5039 is one of a handful of $\gamma$-ray binary systems in the Milky Way, comprising a pulsar and a massive O-type companion star with an orbital period of 3.9 day. Recently, we conducted a data analysis using approximately 16 year of Fermi-LAT observations, spanning from 2008 August 4 to 2024 July 8. In our timing analysis, we discovered two new periodic signals with frequencies higher and lower than the known orbital period. The higher-frequency signal has a period of 3.63819 day with a 7.1$\sigma$ confidence level, while the lower-frequency signal has a period of 4.21654 day with a 6.3$\sigma$ confidence level. Additionally, in data from the High Energy Stereoscopic System of Cherenkov Telescopes, two potential signals with periods similar to the two newly discovered ones. Considering that these two signals fall within the same frequency interval as the orbital period, we suggest the possibility of a third body orbiting the barycenter of the LS 5039 binary system, with the new periodic signals arising from specific frequency combinations of the two orbital periods.