Mass and orbit constraints of the gamma-ray binary LS 5039

TL;DR

This study refines the orbital parameters of the gamma-ray binary LS 5039, indicating a lower eccentricity and suggesting the compact object has a mass exceeding 1.8 solar masses, based on combined photometric and spectroscopic data.

Contribution

It provides updated orbital and physical parameters for LS 5039, including a lower eccentricity and a higher mass estimate for the compact object, using new observational data.

Findings

Lower orbital eccentricity than previous estimates

Optical variability at the orbital period is below 2 mmag

Mass of the compact object is greater than 1.8 solar masses

Abstract

We present the results of space-based photometric and ground-based spectroscopic observing campaigns on the gamma-ray binary LS 5039. The new orbital and physical parameters of the system are similar to former results, except we found a lower eccentricity. Our MOST-data show that any broad-band optical photometric variability at the orbital period is below the 2 mmag level. Light curve simulations support the lower value of eccentricity and imply that the mass of the compact object is higher than 1.8 solar masses.