150 keV Emission from PKS 2149−306 withBEPPOSAX

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Abstract
A BeppoSAX observation of the z = 2.34 quasar PKS 2149-306 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 BeppoSAX spectrum spans almost three decades (0.3-150 keV, quasar frame) and shows an extremely hard (α = 0.4 ± 0.05) X-ray spectrum above 3 keV (comparable to XJB the X-ray background slope), and either a softer (α = 1.0) low-energy component, or an ionized absorber at zero redshift. No evidence is seen of an Fe-K emission line (EW < 167 eV at 6.5 keV quasar frame), a Compton hump (R < 0.3). A bremsstrahlung fit gives kT(rest) = 46 keV, similar to the X-ray background value, and a high-energy cut off power law requires Ecut > 120 keV (quasar frame). The SED of PKS 2149-306 shows two peaks at ~1012±0.5 Hz and ~1021±1.0 Hz (~0.3 mm and ~4 MeV), strongly resembling a low-energy cut off 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.

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