Swift J053041.9-665426, a new Be/X-ray binary pulsar in the Large Magellanic Cloud

Abstract

Aims. We observed the newly discovered X-ray source Swift J053041.9-665426in the X-ray and optical regime to confirm its proposed nature as a high mass X-ray binary. Methods. We obtained XMM-Newton and Swift X-ray data, along with optical observations with the ESO Faint Object Spectrograph, to investigate the spectral and temporal characteristics of Swift J053041.9-665426. Results. The XMM-Newton data show coherent X-ray pulsations with a period of 28.77521(10) s (1σ). The X-ray spectrum can be modelled by an absorbed power law with photon index within the range 0.76 to 0.87. The addition of a black body component increases the quality of the fit but also leads to strong dependences of the photon index, black-body temperature and absorption column density. We identified the only optical counterpart within the error circle of XMM-Newton at an angular distance of ∼0.8′′, which is 2MASS J05304215-6654303. We performed optical spectroscopy from which we classify the companion as a B0-1.5Ve star. Conclusions. The X-ray pulsations and long-term variability, as well as the properties of the optical counterpart, confirm that Swift J053041.9-665426 is a new Be/X-ray binary pulsar in the Large Magellanic Cloud. © 2013 ESO.