Discovery of the new intermediate polar RXJ0558.0+5353.

We report the discovery of a new intermediate polar, detected during the ROSAT all-sky survey. In the course of an optical identification program for galactic plane sources with |b|<20deg a V=14.6mag cataclysmic variable was found as optical counterpart of a soft ROSAT source. A follow-up pointed observation revealed a modulation in the soft X-ray flux with a pulse period of 272.74s indicating the spin period of the white dwarf. The modulation depth increases with decreasing energy and pulse phase resolved spectroscopy shows the X-ray spectrum consists of a variable blackbody component with kT around 57eV and a weak hard tail. The variations in the blackbody component are consistent with changes in the normalization only, suggesting geometric effects as origin. Optical follow-up spectroscopy revealed a binary period of 4.15 hours.