Broadband study of the Be/X-ray binary pulsar eRASSU J012422.9-724248 in the Magellanic Bridge, near the Eastern Wing of the Small Magellanic Cloud

TL;DR

This study confirms eRASSU J012422.9-724248 as a persistent Be/X-ray binary pulsar in the Magellanic Bridge, providing broadband timing and spectral analysis that reveals its spin and orbital periods, and suggests a tentative cyclotron feature.

Contribution

First broadband timing and spectral analysis of the new Be/X-ray binary pulsar eRASSU J012422.9-724248, establishing its persistent nature and key system parameters.

Findings

Detected pulsation at 341.71 s in NuSTAR data.

Inferred orbital period of 63.65 days from OGLE data.

Tentative CRSF at ~12.3 keV with 1.8-sigma significance.

Abstract

The first four all-sky surveys with eROSITA the soft X-ray instrument on board the Spektrum-Roentgen-Gamma (SRG) satellite revealed a new X-ray source, eRASSU J012422.9-724248, in the Magellanic Bridge, near the Eastern Wing of the Small Magellanic Cloud (SMC). We performed a broadband timing and spectral analysis using the optical and X-ray data of eRASSU J012422.9-724248. Using the X-ray observations with eROSITA, Swift, NuSTAR and optical data from the optical Gravitational Lensing Experiment (OGLE) and the Las Cumbres Observatory (LCO), we confirm the nature of eRASSU J012422.9-724248 as a Be/X-ray binary (BeXRB) pulsar in the Magellanic bridge. The position is coincident with that of an early-type star (OGLE ID SMC732.10.7). We detect the spin period at 341.71 s in NuSTAR data and infer a period of 63.65 days from the 15 year monitoring with OGLE, that we interpret as the orbital period of the system. A tentative CRSF at ~12.3 keV is identified in NuSTAR spectra with ~1.8-sigma. The source appears to show a persistent X-ray luminosity and an optical magnitude transition on the long timescale. We propose eRASSU J012422.9-724248 is a new member of the class of persistent BeXRBs.