A quantitative model of coherent, stimulated emission in astrophysical jets

Abstract

On the basis of issues raised by observations of BL Lac objects and the qualitative jet model proposed by Baker et al. in 1988, we have been led to consider the quantitative role of coherent, stimulated emission in jets and construct a new jet model of blazars in which a relativistic electron beam with an axial symmetric, power-law distribution is injected from the central engine into the jet plasma. We study quantitatively the synchrotron emission of the relativistic electron beams. Using the weak turbulent theory of plasma, we discuss the interaction between relativistic electron beams and jet plasma, and the roles of stimulated emission. The main results are: (1) The synchrotron emission increases sensitively with the increase of the angle between the direction of the beam and the magnetic field. When the direction of the beam is vertical to the magnetic field, the synchrotron emission reaches its maximum, i.e. the emitted waves are beamed in the direction of the jet axis. We suggest that radio selected BL Lac objects belong to this extreme classification. (2) The synchrotron emission of the relativistic beam increases rapidly with the increase of the Lorentz factor of the relativistic electron, gamma, when gamma less-than-or-equal-to 22.5, then decreases rapidly with increase of (3) The stimulated emission also increases with increasing Lorentz factor gamma of the relativistic electrons when gamma less-than-or-equal-to 35 and then decreases with the increasing gamma. The maximum stimulated emission and the maximum synchrotron emission occur at different frequencies. Stimulated emission is probably very important and reasonable flare mechanism in blazars. (4) The rapid polarization position angle (PA) swings may arise from the interaction between the relativistic electron beam and the turbulent plasma.