Deep Chandra observations of TeV binaries II: LS 5039

TL;DR

This study used deep Chandra X-ray observations of LS 5039 to search for pulsations, setting the most stringent upper limits to date and constraining the nature of potential pulsar contributions in this TeV binary system.

Contribution

It provides the deepest X-ray pulsation search for LS 5039, constraining the properties of a possible pulsar and its contribution to the system's emission.

Findings

No periodic signals detected in the 0.3-0.4 and 0.75-0.9 orbital phases.

Set an upper limit of ~15% on pulsed fraction for potential pulsar signals.

If a pulsar exists, it is either very fast-spinning, beamed away, or contributes minimally to X-ray emission.

Abstract

We report on Chandra observations of the TeV emitting High Mass X-ray Binary LS 5039, for a total exposure of ~70ks, using the ACIS-S camera in Continuos Clocking mode to search for a possible X-ray pulsar in this system. We did not find any periodic or quasi-periodic signal in the 0.3-0.4 and 0.75-0.9 orbital phases, and in a frequency range of 0.005-175 Hz. We derived an average pulsed fraction 3sigma upper limit for the presence of a periodic signal of ~15% (depending on the frequency and the energy band), the deepest limit ever reached for this object. If the X-ray emission of LS 5039 is due (at least in part) to a rotational powered pulsar, the latter is either spinning faster than ~5.6 ms, or having a beam pointing away from our line of sight, or contributing to ~15% of the total X-ray emission of the system in the orbital phases we observed.