keV Emission from PKS 2149 − 306 with BeppoSAX

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 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 −0.3) low energy component, or an ionized absorber at zero redshift. No evidence is seen of an Fe-K emission line (EW<50 eV at 6.5 keV quasar frame), a Compton hump (R < 0.3) or the strong 17 keV (quasar frame) emission line (EW<20 eV, quasar frame) previously reported by Yaqoob et al. (1999). A bremsstrahlung fit gives kT(rest)=46 −16 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 ∼10Hz and ∼10Hz (∼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. Subject headings: quasars – emission mechanisms X-rays Gamma-rays