RADIO AND X-RAY BEAMING IN STEEP-SPECTRUM QUASARS

Soft X-ray fluxes have been drawn from the ROSAT All Sky Survey for an unbiased sample of low-frequency-selected radio quasars, the Molonglo Quasar Sample. In agreement with previous studies a close relationship is found between the radio-core and X-ray luminosities, with steep-spectrum quasars following a shallower correlation slope than flat-spectrum objects. Using the core-to-lobe flux density ratio, R, as an orientation indicator, we can study further the aspect dependence of the X-ray emission components in steep-spectrum quasars. In this way, we trace the presence of a highly anisotropic X-ray component, related to the radio core and consistent with Doppler-boosted models. The orientation dependence of this beamed component, together with sample selection effects, can explain fully the different behaviour of quasars in the radio-core-X-ray luminosity plane, which is found to be a strong function of R. A continuous variation of the relative strength of the beamed component with R is in agreement with the unified schemes which describe steep- and flat-spectrum quasars as members of the same population differing only in orientation.