The eclipsing X-ray pulsar X-7 in M33

Using our extensive ROSAT X-ray observations of M33, we confirm a 3.45-d ec lipse period for the Einstein source X-7 proposed by Larson & Schulman and discover evidence for a 0.31-s pulse period. The orbital period, pulse peri od and observed X-ray luminosity are remarkably similar to those of the Sma ll Magellanic Cloud high-mass X-ray binary SMC X-l, We therefore suggest th at M33 X-7 is a neutron star high-mass X-ray binary with a 15-40 M. O/B com panion and a binary separation of 25-33 R. if the companion is almost filli ng its Roche lobe.