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Conference Paper

Synchrotron X-ray Emission from Flat-spectrum Radio Quasars


Costamante,  L.
Division Prof. Dr. Werner Hofmann, MPI for Nuclear Physics, Max Planck Society;

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Padovani, P., Costamante, L., Ghisellini, G., Giommi, P., & Perlman, E. (2003). Synchrotron X-ray Emission from Flat-spectrum Radio Quasars. In L. O. Takalo, & E. Valtaoja (Eds.), High Energy Blazar Astronomy, ASP Conference Proceedings. San Francisco: Astronomical Society of the Pacific.

Cite as: http://hdl.handle.net/11858/00-001M-0000-0011-8E87-B
We present new BeppoSAX observations of four flat-spectrum radio quasars (FSRQ) with spectral energy distributions similar to those of high-energy peaked BL Lacs. In one of our sources the BeppoSAX band is dominated by synchrotron emission peaking at ∼ 2 × 1016 Hz, as also shown by its steep (energy index αx ∼ 1.5) spectrum. This makes this object the first known FSRQ whose X-ray emission is not due to inverse Compton radiation. Two other sources display a flat X-ray spectrum (αx ∼ 0.7) but with indications of steepening at low energies. In these objects, the combination of BeppoSAX and ROSAT observations, (non-simultaneous) multifrequency data, and a synchrotron inverse Compton model suggest synchrotron peak frequencies ≈ 1015 Hz, although a better coverage of the spectral energy distributions is needed to provide firmer values. Our sources, although firmly in the radio--loud regime, have powers more typical of high--energy peaked BL Lacs than of FSRQ, and indeed their radio powers put them near the low--luminosity end of the FSRQ luminosity function. We discuss this in terms of an anti-correlation between synchrotron peak frequency and total power, based on physical arguments, and also as possibly due to a selection effect.