ROSAT SPECTRA OF QUASARS

X-ray observations of AGN with Einstein, EXOSAT and Ginga have shown t hat the spectra of quasars in the energy range from 2 to 10 keV can be approximately described by a single power law model with a photon ind ex of 1.7 - 2.0. They also suggested that a soft X-ray excess componen t (below approximate to 1 keV) is a common feature in many quasars. In order to investigate the properties of the soft excess in radio-loud quasars we analysed the data of the pointed ROSAT/PSPC observations of the six radio-loud quasars PG 0007+106, PKS 0135-247, QSO 0537-286, Q SO 0923+392, PG 1225+317, 3C 273. To these objects we added also the d ata of the radio-quiet quasar PG 0804+761. In four cases (including th e radio-quiet object) we find that the spectra in the PSPC sensitivity hand are considerably steeper than the spectra above 2 keV, a clear s ignature for a soft X-ray excess. In the ether three objects the soft component could be hidden by the interstellar absorption or by the lar ge redshift (z > 2) and can not be excluded. We point out the limits o f the detectability of a soft component with the ROSAT/PSPC detector d ue to these effects. The comparison of different spectral models for t he soft component (power law, thermal bremsstrahlung, black body) sugg est that the soft component must decline very rapidly towards the high er energies.