Broadband study and the discovery of pulsations from the Be/X-ray binary eRASSU J052914.9−662446 in the Large Magellanic Cloud

Abstract

Context. The Magellanic Clouds are our nearest star-forming galaxies. While the population of high-mass X-ray binaries (HMXBs) in the Small Magellanic Cloud is relatively well studied, our knowledge about the Large Magellanic Cloud (LMC) is far from complete given its large angular extent and the insufficient coverage with X-ray observations. Aims. We conducted a search for new HMXBs in the LMC using data from eROSITA, the soft X-ray instrument on board the Spektrum-Roentgen-Gamma satellite. Methods. After confirming the nature of eRASSU J052914.9−662446 as a hard X-ray source that is positionally coincident with an early-type star, we followed it up with optical spectroscopic observations from the South African Large Telescope (SALT) and a dedicated NuSTAR observation. Results. We study the broadband timing and spectral behaviour of the newly discovered HMXB eRASSU J052914.9−662446 through eROSITA, Swift, and NuSTAR data in X-rays and the Optical Gravitational Lensing Experiment (OGLE) and SALT RSS data at the optical wavelength. We report the detection of a spin period at 1412 s and suggest that the orbital period of the system is ∼151 days. We thereby establish that eRASSU J052914.9−662446 is an accreting pulsar. Furthermore, through optical spectroscopic observations and the detection of Hα emission, the source is identified as a Be X-ray binary pulsar in the LMC. We also investigated the variability of the source in the optical and X-ray regime over the past decades and provide estimates of the possible magnetic field strength of the neutron star.