Near-periodical spin period evolution in the binary system LMC X-4

TL;DR

This study analyzes over 43 years of X-ray data of LMC X-4, revealing near-periodical spin period variations approximately every 6.8 years, indicating long-term spin torque reversals in this high-mass X-ray binary.

Contribution

It is the first to identify near-periodical spin period variations in LMC X-4 over decades, highlighting long-term spin torque reversals in the system.

Findings

Detected 6.8-year near-periodical spin variations

LMC X-4 exhibits long-term spin torque reversals

First long-term analysis of spin evolution in LMC X-4

Abstract

In this paper we investigated the long-term evolution of the pulse-period in the high-mass X-ray binary LMC X-4 by taking advantage of more than 43~yrs of measurements in the X-ray domain. Our analysis revealed for the first time that the source is displaying near-periodical variations of its spin period on a time scale of roughly 6.8~yrs, making LMC X-4 one of the known binary systems showing remarkable long term spin torque reversals. We discuss different scenarios to interpret the origin of these torque reversals.