The identification of the long-period X-ray pulsar 1WGA J1958.2+323 with a Be-star/X-ray binary

Abstract

We present the results of optical observations performed between May and September 1998 of the stars within the position error circle of the recently discovered 12min pulsating X-ray source 1WGA J1958.2+3232. Based on photometry and slitless spectroscopy, we selected a likely optical counterpart, which was subsequently determined to be a m_V=15.7 B0Ve star, the spectral properties of which are in good agreement with the X-ray results. The proposed optical counterpart shows several H, He and Fe emission-lines, while the interstellar absorption spectral features place the star at a distance of about 800 pc.The inferred X-ray luminosity for this distance is about 10^33 erg s^-1 in the 2--10 keV band. We conclude that 1WGA J1958.2+3232 is a likely new long-period low-luminosity accreting neutron star in a Be-star/X-ray binary system.