  The eclipsing X-ray binary M33 X-7 was in the field of view during several
observations of our XMM-Newton M33 survey and in the archival Chanfdra
observation 1730 which cover a large part of the 3.45 d orbital period. We
detect emission of M33 X-7 during eclipse and a soft X-ray spectrum of the
source out of eclipse that can best be described by bremsstrahlung or disk
blackbody models. No significant regular pulsations of the source in the range
0.25-1000 s were found. The average source luminosity out of eclipse is 5E37
erg/s (0.5-4.5 keV). In a special analysis of DIRECT observations we identify
as optical counterpart a B0I to O7I star of 18.89 mag in V which shows the
ellipsoidal heating light curve of a high mass X-ray binary with the M33 X-7
binary period. The location of the X-ray eclipse and the optical minima allow
us to determine an improved binary period and ephemeris of mid-eclipse as HJD
(2451760.61+-0.09)+- N * (3.45376+-0.00021). The mass of the compact object
derived from orbital parameters and the optical companion mass, the lack of
pulsations, and the X-ray spectrum of M33 X-7 may indicate that the compact
object in the system is a black hole. M33 X-7 would be the first detected
eclipsing high mass black hole X-ray binary.
