Discovery of X-ray pulsations in the Be/X-ray binary IGR J21343+4738

We report on the discovery of X-ray pulsations in the Be/X-ray binary IGR J21343+4738 during an XMM-Newton observation. We obtained a barycentric corrected pulse period of 320.35 ± 0.06 s. The pulse profile displays a peak at low energy that flattens at high energy. The pulse fraction is 45 ± 3 per cent and independent of energy within the statistical uncertainties. The 0.2-12 keV spectrum is well fitted by a two-component model consisting of a blackbody with kT = 0.11 ± 0.01 keV and a power law with photon index Γ = 1.02 ± 0.07. Both components are affected by photoelectric absorption with an equivalent hydrogen column density N_H = (1.08 ± 0.15) × 10²² cm^-2. The observed unabsorbed flux is 1.4 × 10^-11 erg cm^-2 s^-1 in the 0.2-12 keV energy band. Despite the fact that the Be star's circumstellar disc has almost vanished, accretion continues to be the main source of high-energy radiation. We argue that the observed X-ray luminosity (L_X ∼ 10³⁵ erg s^-1) may result from accretion via a low-velocity equatorial wind from the optical companion.