The nature of the nuclear X-ray emission of radio-loud quasars

The X-ray luminosities of radio-loud quasars (RLQs) are higher than those of radio-quiet quasars (RQQs) at a matched L_uv by a factor of ≈3 on average. Using a uniform sample of 729 optically selected RLQs, we found that the L_x-L_uv relation for steep-spectrum RLQs is quantitatively similar in slope to that of RQQs, which supports the idea that the coronae of RLQs are intrinsically X-ray brighter than those of RQQs; this result challenges previous thinking about the nature of the nuclear X-ray emission of RLQs over the past ≈35 years where the excess X-ray emission of RLQs is caused by a distinct, jet-linked X-ray component. We also investigated the X-ray spectral and variability properties of these RLQs using serendipitous Chandra and XMM-Newton observations that minimize potential selection biases. The X-ray spectral shape of RLQs is not significantly different from that of RQQs, supporting a common “coronal” origin of their X-ray emission. Furthermore, the X-ray variability amplitude is generally smaller than that of RQQs, the implications of which are also discussed.