Multi-wavelength properties of IGR J05007-7047 (LXP 38.55) and identification as a Be X-ray binary pulsar in the LMC

TL;DR

This study presents a detailed multi-wavelength analysis of the Be X-ray binary IGR J05007-7047 in the LMC, confirming its pulsar nature, orbital period, and spectral properties through X-ray and optical observations.

Contribution

It is the first to identify the system as a pulsar with a 38.55 s period and determine its orbital period using combined X-ray and optical data.

Findings

Detected coherent X-ray pulsations at 38.55 s.

Confirmed the orbital period as approximately 30.78 days.

Characterized the X-ray spectrum with an absorbed power law and high-temperature black-body.

Abstract

We report on the results of a $\sim$40 d multi-wavelength monitoring of the Be X-ray binary system IGR J05007-7047 (LXP 38.55). During that period the system was monitored in the X-rays using the Swift telescope and in the optical with multiple instruments. When the X-ray luminosity exceeded $10^{36}$ erg/s we triggered an XMM-Newton ToO observation. Timing analysis of the photon events collected during the XMM-Newton observation reveals coherent X-ray pulsations with a period of 38.551(3) s (1 {\sigma}), making it the 17$^{th}$ known high-mass X-ray binary pulsar in the LMC. During the outburst, the X-ray spectrum is fitted best with a model composed of an absorbed power law ($\Gamma =0.63$) plus a high-temperature black-body (kT $\sim$ 2 keV) component. By analysing $\sim$12 yr of available OGLE optical data we derived a 30.776(5) d optical period, confirming the previously reported X-ray period of the system as its orbital period. During our X-ray monitoring the system showed limited optical variability while its IR flux varied in phase with the X-ray luminosity, which implies the presence of a disk-like component adding cooler light to the spectral energy distribution of the system.