IS THE HIGH-ENERGY EMISSION FROM CENTAURUS A COMPTON-SCATTERED JET RADIATION

We consider whether the hard X-ray and soft gamma-ray emission from Centaurus A is beamed radiation from the active nucleus that is Compton-scattered into our line of sight. We derive the spectrum and degree of polarization of scattered radiation when incident beamed radiation is scattered from a cold (kT much less than m(e)c2) electron cloud moving with bulk relativistic motion along the jet axis, and calculate results for an unpolarized, highly beamed incident power-law photon source. We fit the OSSE data from Centaurus A with this model and find that if the scatterers are not moving relativistically, then the angle the jet makes with respect to our line of sight is 61-degrees + 5-degrees. We predict a high degree of polarization of the scattered radiation below approximately 300 keV. Future measurements with X-ray and gamma-ray polarimeters could be used to constrain or rule out such a scenario.