X-RAY-SPECTRUM OF THE HIGH-POLARIZATION QUASAR PKS-1510-089

We present results from the X-ray spectra of the radio-loud, high-pola rization quasar PKS 1510-089, based on new data obtained using ASCA an d from archival ROSAT data. We find the X-ray spectrum obtained by ASC A to be unusually hard, with the photon index Gamma = 1.30 +/- 0.06, w hile the (nonsimultaneous) ROSAT data indicate a steeper spectrum with Gamma = 1.9 +/- 0.3. However, we find the X-ray flux at 1 keV to be w ithin similar to 10% during both observations. Thus, we suggest the mo st likely explanation is that there is a break (with Delta Gamma great er than or equal to 0.6) in the underlying continuum at similar to 0.7 keV. Although the sample of high-polarization quasars for which high- duality X-ray spectra are available is small, flat X-ray spectra seem to be characteristic of these objects, and they also appear to be hard er than that of the other radio-loud but low-polarization quasars. The multiwavelength spectrum of PKS 1510-089 is similar to many other gam ma-ray blazars, suggesting the emission is dominated by that from a re lativistic jet. A big blue bump is also seen in its multiwavelength sp ectrum, suggesting the presence of a strong thermal component as well.