RXJ0123.4-7321, a Be/X-ray binary in the wing of the SMC

TL;DR

This study confirms RXJ0123.4-7321 as a Be/X-ray binary in the SMC wing by analyzing archival X-ray and optical data, revealing significant variability and periodic outbursts indicative of its binary nature.

Contribution

The paper identifies and characterizes a new Be/X-ray binary in the SMC wing through archival data analysis, highlighting its variability and orbital period.

Findings

X-ray flux varied by a factor of ~150 between ROSAT and XMM-Newton observations.

Detected a long-term optical variability with a 119.9-day period.

Confirmed the system as a Be/X-ray binary in the SMC wing.

Abstract

To confirm faint Be/X-ray binary candidates from the XMM-Newton survey of the Small Magellanic Cloud, we searched for X-ray outbursts in archival ROSAT observations. We found that RXJ0123.4-7321 was much brighter when detected with ROSAT than seen 16 years later by XMM-Newton. We analysed the ROSAT observations and the OGLE I-band light curve of the optical counterpart to investigate the nature of the system. High long-term variability in the X-ray flux of a factor of ~150 was found between the ROSAT and XMM-Newton detections, indicating strong outburst activity during the ROSAT observations. The I-band light curve reveals long-term variability and regular outbursts with a period of (119.9+-2.5) days indicating the orbital period of the binary system. The large X-ray flux variations and the properties of the optical counterpart confirm RXJ0123.4-7321 as a new Be/X-ray binary in the wing of the Small Magellanic Cloud.