An emission mechanism for extragalactic radio jets

Abstract

The observed emtsswns of radio waves from extragalactic radio jets are customarily interpreted in terms of the incoherent synchrotron radiation produced by a nonthermal population of relativistic electrons (or positrons) gyrating in a magnetic field. Such an interpretation requires, by necessity, a mechanism (or mechanisms) to constantly reenergize the particles in directions transverse to the magnetic field in momentum space. This paper, on the other hand, presents a possible alternative mechanism for radiation emission that does not require transverse reacceleration, albeit the theory is only preliminary at this stage. The emission mechanism described in the present paper is an induced plasma process that results from a nonlinear coupling of the electrostatic beam mode with the transverse electromagnetic mode. The beam mode is excited when a stream of ultrarelativistic electron-positron pair plasma nonlinearly interacts with low-frequency intrinsic turbulence. The only source of free energy for the instability is the streaming motion of the pair plasma. Therefore, as opposed to the incoherent synchrotron model, this mechanism (if, indeed, it is operative) has an advantage of not having to rely on the concept of constant renenergization of particles in the transverse direction.