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Martin Elvis, Fabrizio Fiore, Aneta Siemiginowska, Smita Mathur, Jonathan McDowell (Harvard-Smithsonian Center for Astrophysics), Jill Bechtold (Steward Observatory, Univ. Arizona)
A BeppoSAX observation of the z=2.34 quasar PKS2149-306 produced a strong signal in the high energy PDS instrument up to a maximum observed energy of nearly 50~keV, 150~keV in the quasar frame. The Beppo-SAX spectrum spans almost 3 decades (0.3-150~keV, quasar frame) and shows a hard (\alpha=0.4±0.05) X-ray spectrum above 3~keV, and either a softer (\alpha=1.0+0.6-0.3) low energy component, or an ionized absorber at zero redshift. An ionized absorber may be blueshifted from the quasar frame with v=0.6c. No evidence is seen of an Fe-K emission line (EW<50~eV at 6.5~keV rest) or a Compton hump (R<0.3). A bremsstrahlung fit gives kT(rest)=46+32-16~keV, similar to the X-ray background value.
The SED of PKS~2149-306 shows two peaks at ~1012\pm 0.5Hz and ~1021\pm 1.0Hz (~0.3~mm and ~4~MeV), strongly resembling a low energy cutoff BL~Lac object (LBL). The ratio of the two peaks shows an extreme Compton dominance (CD=1.4±0.4), as in flat spectrum radio quasars (FSRQs).
The presence of an additional `optical/UV big bump' component may provide photons that cool the jet, suppressing the radio emission. Compton suppression amplifies changes in intrinsic jet power into a greater change in radio loudness. Hence a modest extension from conditions in PKS2149--306 may completely quench a radio jet. The result would be a radio-quiet quasar. Several predictions of the radio and X-ray properties of radio-quiet AGN follow from this picture.
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