ROSAT PSPC SPECTRA OF 6 PG QUASARS AND PHL-1657

We report results from the spectral analysis of pointed ROSAT PSPC obs ervations of six PG quasars and the weak-bump quasar PHL 1657. Disrega rding other frequency bands, the PSPC data are represented best by sim ple power-law source spectra (dN/dE proportional to E(Gamma)) with a s lope Gamma = -2.5 +/- 0.4 and do not show evidence for a more complex structure. However, within the limits given by statistics and systemat ical errors, a superposition of two power-law spectra, which allows a connection to the observed UV fluxes and to the generally flatter hard -X-ray spectra observed by EXOSAT and Ginga, is found to be indistingu ishable from a simple power-law in the PSPC energy band. For the PG qu asars, a direct connection to the observed UV flux is obtained with a steep soft-X-ray slope Gamma(sx) = -3.1 +/- 0.3, fixing the hard-X-ray slope. For PHL 1657, the soft-X-ray spectrum seen by ROSAT is much st eeper than the Ginga spectrum, rising towards the EUV in nu F-nu, and it can not be extrapolated down to meet the exceptionally weak UV flux . A Wien-shaped thermal UV/soft-X-ray bump with a temperature of simil ar to 50 eV connects the UV and soft-X-ray spectra in all cases, but g ives only a poor representation of the high signal-to-noise PSPC spect ra. We discuss implications of our results for models of the X-ray emi ssion in quasars. Three more pointed PSPC observations, covering the r adio galaxies 3C3433, 3C83.1 and the quasar PG2214+139 (Mkn 304), did not yield enough counts for a spectral analysis. sis. For these source s, and four high redshift quasars from the Hewitt & Burbidge catalogue located in the observation fields, we present brief results or limits for their soft-X-ray fluxes.