ROSAT Observations of Blazars from a Polarized Radio Selected Sample

Abstract

We have observed with ROSAT six blazars from the sample of 31 polarized objects constructed by Impey and Tapia (1988). Results of the spectral analysis in the ROSAT band of three objects, PKS 0301-243, PKS 1055+018 and PG 1424+240 are presented here and compared with the three previously published objects. Using a simple power law model with free absorption a wide range of spectral slopes is found. Objects with emission lines have flatter X-ray spectra than lineless objects. Indication of spectral curvature within the X-ray band is found in the sense of a concavity (soft excess) for the flattest spectrum and a convexity (soft deficiency) for the steepest one. The X-ray spectral shape is discussed in relation to the overall energy distribution for the six objects. The results are compared with other samples of blazars. The X-ray spectral index, alpha_X, is found to be anticorrelated with the broad band spectral index alpha_RO and with bolometric luminosity and redshift. It is suggested that the different spectra of quasar-like and BL Lac-like blazars represent extremes in a continuous distribution rather than two distinct populations.