The X-ray spectral and variability properties of typical radio-loud quasars

Abstract

We present X-ray spectral and long-term variability analyses of an unbiased sample of 361 optically selected radio-loud quasars (RLQs) utilizing sensitive serendipitous X-ray data from the Chandra and XMM-Newton archives. The spectral and temporal properties of RLQs are compared with those of radio-quiet quasars (RQQs) matched in 𝐿 2500Å and 𝑧. The median power-law photon index (Γ) of RLQs is 1.84 +0.01 −0.01 , which is close to that of matched RQQs (1.90 +0.02 −0.01 ). No significant correlations between Γ and radio-loudness, 𝐿 x /𝐿 x,rqq (the X-ray luminosity over that expected from the 𝐿 x -𝐿 uv relation for RQQs), redshift, or Eddington ratio are found for our RLQs. The stacked X-ray spectra of our RLQs show strong iron-line emission and a possible Compton-reflection hump. The intrinsic X-ray variability amplitude is ≈ 40% for RLQs on timescales of months-to-years in the rest frame, which is somewhat smaller than for the matched RQQs (≈ 60%) on similar timescales, perhaps due to the larger black-hole masses and lower Eddington ratios in our RLQ sample. The X-ray spectral and variability results for our RLQs generally support the idea that the X-ray emission of typical RLQs is dominated by the disk/corona, as is also indicated by a recent luminosity correlation study.