The Orbits of the Gamma-ray Binaries LS I +61 303 and LS 5039

TL;DR

This paper refines the orbital parameters of two gamma-ray binaries, LS I +61 61 303 and LS 5039, using new optical spectra, which enhances understanding of their high-energy emission regions.

Contribution

The study provides improved orbital solutions for LS I +61 61 303 and LS 5039, resolving previous discrepancies and aiding high-energy emission analysis.

Findings

Updated orbital elements for LS I +61 61 303 and LS 5039.

Resolution of previous orbital solution discrepancies.

Enhanced understanding of high-energy emission regions.

Abstract

LS I +61 303 and LS 5039 are two of only a handful of known high mass X-ray binaries (HMXBs) that exhibit very high energy emission in the MeV-TeV range, and these "gamma-ray binaries" are of renewed interest due to the recent launch of the Fermi Gamma-ray Space Telescope. Here we present new radial velocities of both systems based on recent red and blue optical spectra. Both systems have somewhat discrepant orbital solutions available in the literature, and our new measurements result in improved orbital elements and resolve the disagreements. The improved geometry of each orbit will aid in studies of the high energy emission region near each source.