First characterization of a new High Mass X-ray Binary in LMC eRASSU J050810.4$-$660653 with SRG/ART-XC, NuSTAR and Swift

TL;DR

This paper presents the first detailed spectral and timing analysis of the new Be/X-ray binary eRASSU J050810.4-660653 in the LMC, revealing pulsations, spectral characteristics, and an estimated orbital period using data from multiple X-ray observatories.

Contribution

It provides the first comprehensive spectral and timing characterization of the newly discovered high-mass X-ray binary in the LMC, including pulsation detection and spectral modeling.

Findings

Detected 40.5781 s pulsations with energy-dependent pulsed fraction.

Estimated orbital period of approximately 38 days.

Spectral analysis indicates a power-law with exponential cutoff, no cyclotron line detected.

Abstract

We report results of the first detailed spectral and temporal studies of the recently discovered Be/X-ray binary eRASSU J050810.4$-$660653 in LMC based on the data from the SRG/ART-XC, NuSTAR and Swift/XRT instruments obtained in December 2021 - May 2022 in a wide energy range of 0.5-79 keV. Pulsations with the period of $40.5781 \pm 0.0004$ s were found in the source light curve with the pulsed fraction monotonically increasing with the energy. An estimate of the orbital period of $\sim38$ days was obtained based on the long-term monitoring of the system. The source spectrum can be well approximated with a power-law model modified by an exponential cutoff at high energies. The pulse phase-resolved spectroscopy shows a strong variation of spectral parameters depending on the phase of a neutron star rotation. We have not found any features connected with the cyclotron absorption line both in the phase-averaged and phase-resolved spectra of eRASSU J050810.4$-$660653. However, the neutron star magnetic field was estimated around several $10^{13}$ G using different indirect methods. Discovered variations of the hardness ratio over the pulse phase is discussed in terms of physical and geometrical properties of the emitting region.