Discovery of SXP265, a Be/X-ray binary pulsar in the Wing of the Small Magellanic Cloud

TL;DR

This paper reports the discovery and detailed characterization of SXP 265, a new Be/X-ray binary pulsar in the Small Magellanic Cloud, including its spectral properties, pulsation period, and optical counterpart.

Contribution

The study provides the first identification and comprehensive analysis of SXP 265 as a Be/X-ray binary pulsar with multi-wavelength observations and spectral classification.

Findings

Detected X-ray pulsations with a 264.516 s period.

Identified the optical counterpart as a B1-2II-IVe star.

Estimated orbital period of approximately 146 days.

Abstract

We identify a new candidate for a Be/X-ray binary in the XMM-Newton slew survey and archival Swift observations that is located in the transition region of the Wing of the Small Magellanic Cloud and the Magellanic Bridge. We investigated and classified this source with follow-up XMM-Newton and optical observations. We model the X-ray spectra and search for periodicities and variability in the X-ray observations and the OGLE I-band light curve. The optical counterpart has been classified spectroscopically, with data obtained at the SAAO 1.9 m telescope, and photometrically, with data obtained using GROND at the MPG 2.2 m telescope. The X-ray spectrum is typical of a high-mass X-ray binary with an accreting neutron star. We detect X-ray pulsations, which reveal a neutron-star spin period of P = (264.516+-0.014) s. The source likely shows a persistent X-ray luminosity of a few 10^35 erg/s and in addition type-I outbursts that indicate an orbital period of ~146 d. A periodicity of 0.867 d, found in the optical light curve, can be explained by non-radial pulsations of the Be star. We identify the optical counterpart and classify it as a B1-2II-IVe star. This confirms SXP 265 as a new Be/X-ray binary pulsar originating in the tidal structure between the Magellanic Clouds.