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

Abstract

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 L2500Å 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 ($1.90_{-0.01}^{+0.02}$). No significant correlations between Γ and radio-loudness, Lx/Lx, rqq (the X-ray luminosity over that expected from the Lx–Luv 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 per cent for RLQs on time-scales of months-to-years in the rest frame, which is somewhat smaller than for the matched RQQs (≈60 per cent) on similar time-scales, 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 disc/corona, as is also indicated by a recent luminosity correlation study.