Abstract
We present a high-quality X-ray spectrum in the 3-53 keV rest frame band of the radio-loud quasar 1508+5714, which is by far the brightest known X-ray source at z > 4. A simple power-law model with an absorption column density equal to the Galactic value in the direction of the source provides an excellent and fully adequate fit to the data; the measured power-law photon index ? = 1.42 -->+ 0.13?0.10. Upper limits to Fe K? line-emission and Compton-reflection components are derived. We offer evidence for both X-ray and radio variability in this object and provide the first contemporaneous radio spectrum (? = -0.25). The data are all consistent with a picture in which the emission from this source is dominated by a relativistically beamed component in both the X-ray and radio bands.
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