X‐Ray and TeV Gamma‐Ray Emission from Parallel Electron‐Positron or Electron‐Proton Beams in BL Lacertae Objects

In this paper we discuss models of the X-rays and TeV gamma-ray emission fromBL Lac objects based on parallel electron-positron or electron-proton beamsthat form close to the central black hole owing to the strong electric fieldsgenerated by the accretion disk and possibly also by the black hole itself.Fitting the energy spectrum of the BL Lac object Mrk 501, we obtain tightconstrains on the beam properties. Launching a sufficiently energetic beamrequires rather strong magnetic fields close to the black hole 100-1000 G.However, the model fits imply that the magnetic field in the emission region isonly 0.02 G. Thus, the particles are accelerated close to the black hole andpropagate a considerable distance before instabilities trigger the dissipationof energy through synchrotron and self-Compton emission. We discuss variousapproaches to generate enough power to drive the jet and, at the same time, toaccelerate particles to 20 TeV energies. Although the parallel beam model hasits own problems, it explains some of the long-standing problems that plaguemodels based on Fermi type particle acceleration, like the presence of a veryhigh minimum Lorentz factor of accelerated particles. We conclude with a briefdiscussion of the implications of the model for the difference between theprocesses of jet formation in BL Lac type objects and in quasars.Comment: Accepted for publication in the Astrophysical Journa