150 keV Emission from PKS 2149−306 withBEPPOSAX

A BeppoSAX observation of the z=2.34 quasar PKS2149-306 produced a strongsignal in the high energy PDS instrument up to a maximum observed energy ofnearly 50 keV, 150 keV in the quasar frame. The Beppo-SAX spectrum spans almost3 decades (0.3-150 keV, quasar frame) and shows an extremely hard(alpha=0.4+/-0.05) X-ray spectrum above 3 keV (comparable to the X-raybackground slope), and either a softer (alpha=1.0(+0.6, -0.3)) low energycomponent, or an ionized absorber at zero redshift. No evidence is seen of anFe-K emission line (EW<167 eV at 6.5 keV quasar frame) or a Compton hump(R<0.3). A bremsstrahlung fit gives kT(rest)=46(+32, -16) keV, similar to theX-ray background value, and a high energy cut-off power law requires E(cut)>120keV (quasar frame). The SED of PKS 2149-306 shows two peaks at ~ 10(12+/-0.5}Hz and\~10(21+/-1.0)Hz (~ 0.3 mm and ~ 4 MeV), strongly resembling a low energycutoff BL~Lac object (LBL). The ratio of the two peaks shows an extreme Comptondominance (C_D=1.4+/- 0.4), as in flat spectrum radio quasars (FSRQs). Thepresence of an additional `optical/UV big bump' component may provide photonsthat cool the jet, suppressing the radio emission.Comment: 18 pages, 3 figures. LaTeX, with AAS .sty file aasms4. Revised to correct a stupid mistake affecting the Fe-K EW. The results now agree with the ASCA data from Yaqoob et a