  We report on the first pointed X-ray observations with XMM-Newton and RXTE
satellites of the X-ray source RXJ0757.0+6306=HT Cam. We detect a strong 515s
X-ray modulation confirming the optical photometric period found in 1998, which
definitively assigns this source to the intermediate polar class of magnetic
cataclysmic variables. The lack of orbital sidebands in the X-rays indicates
that the X-ray period is the spin period of the accreting white dwarf.
Simultaneous ultraviolet and optical B-band photometry acquired with the
XMM-Newton Optical Monitor and coordinated optical UBVRI photometric data
acquired at the Nordic Optical Telescope (La Palma) show that the optical pulse
is in phase with the X-rays and hence originates in the magnetically confined
accretion flow. The lack of ultraviolet spin modulation suggests that
accretion-induced heating on the white dwarf surface is not important in this
source. Spectral analyses of XMM-Newton EPIC and RGS spectra show that HT Cam
has a multi-temperature spectrum and, contrary to most intermediate polars, it
does not suffer from strong absorption. With its 86min orbital period, HT Cam
is then the third confirmed system of this class below the 2-3hr period gap
accreting at a low rate.
