On the Hadronic Beam Model for Gamma‐Ray Production in Blazars

We consider, herein, a model for gamma-ray production in blazars in which arelativistic, highly-collimated electron-proton beam interacts with a dense,compact cloud as the jet propagates through the broad and perhaps narrow lineregions (BLR and NLR) of active galactic nuclei (AGN). During the propagationof the beam through the cloud, the process of excitation of plasma wavesbecomes an important energy loss mechanism, especially for mildly relativisticproton beams. We compute the expected spectra of gamma-rays from the decay ofneutral pions produced in hadronic collisions of the beam with the cloud,taking into account collisionless losses of the electron-proton beam. Thismodel may explain the X-ray and TeV gamma-ray (both low and high emissionstates) of Mrk 421 as a result of synchrotron emission of secondary pairs fromthe decay of charged pions and gamma-ray emission from the decay of neutralpions for the plausible cloud parameters. However clouds can not be too hot andtoo dense. Otherwise the TeV gamma-rays can be attenuated by the bremsstrahlungradiation in the cloud and the secondary pairs are not able to efficientlyproduce synchrotron flares because of the dominant role of inverse Comptonscattering. The non-variable $\gamma$-ray emission observed from Mrk 421 in the EGRETenergy range cannot be described by the $\gamma$-rays from decay of neutralpions provided that the spectrum of protons in the beam is well described by asimple power law. These $\gamma$-rays might only be produced by secondary pairsscattering the soft non-variable X-rays which might originate in the inner partof the accretion disk.Comment: 14 pages,3 figures, latex, submitted to Ap