Identification of two new HMXBs in the LMC: a $\sim$2013 s pulsar and a probable SFXT

TL;DR

This study reports the discovery of two high-mass X-ray binary systems in the Large Magellanic Cloud, including a new pulsar and a probable supergiant fast X-ray transient, based on X-ray and optical observations.

Contribution

It identifies and characterizes two new HMXBs in the LMC, including the first confirmed pulsar and a rare SFXT candidate outside our Galaxy.

Findings

Detection of a 2013 s pulsar in the LMC.

Identification of a probable SFXT with flaring behavior.

Both systems classified as supergiant X-ray binaries.

Abstract

We report on the X-ray and optical properties of two high-mass X-ray binary systems located in the Large Magellanic Cloud (LMC). Based on the obtained optical spectra, we classify the massive companion as a supergiant star in both systems. Timing analysis of the X-ray events collected by XMM-Newton revealed the presence of coherent pulsations (spin period $\sim$2013 s) for XMMU J053108.3-690923 and fast flaring behaviour for XMMU J053320.8-684122. The X-ray spectra of both systems can be modelled sufficiently well by an absorbed power-law, yielding hard spectra and high intrinsic absorption from the environment of the systems. Due to their combined X-ray and optical properties we classify both systems as SgXRBs: the 19$^{\rm th}$ confirmed X-ray pulsar and a probable supergiant fast X-ray transient in the LMC, the second such candidate outside our Galaxy.