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 Gamma = 1.02 +/- 0.07. Both components are affected by photoelectric absorption with an equivalent hydrogen column density N-H = (1.08 +/- 0.15) x 10(22) cm(-2). The observed unabsorbed flux is 1.4 x 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 similar to 10(35) erg s(-1)) may result from accretion via a low-velocity equatorial wind from the optical companion.