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 $L_{2500A}$ and $z$. The median power-law photon index ($\Gamma$) 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 $\Gamma$ and radio-loudness, $L_{\mathrm{x}}/L_{\mathrm{x},\mathrm{rqq}}$ (the X-ray luminosity over that expected from the $L_{\mathrm{x}}$-$L_{\mathrm{uv}}$ 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 $\approx 40$% for RLQs on timescales of months-to-years in the rest frame, which is somewhat smaller than for the matched RQQs ($\approx 60$%) 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.

19 pages, 11 figures, accepted for publication in MNRAS

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