Two Blobs in a Jet Model for the γ-Ray Emission in Radio Galaxies

Abstract

Abstract In the unified scheme, FR I type radio galaxies are identified with the blazar type active galaxies for which jets are aligned at large angles to the line of sight. A few radio galaxies of this type have been discovered to emit GeV–TeV gamma-rays. We consider a scenario that naturally explains the very high energy gamma-ray emission at large angles to the jet axis. It is proposed that two emission regions are present in the jet at this same moment. The inner region (blob I) moves with the large Lorentz factor, producing radiation strongly collimated along the jet axis, as observed in BL Lac type blazars. On the other hand, the outer region (blob II), which moves with the mild Lorentz factor, contains isotropically distributed relativistic electrons in the blob reference frame. These electrons upscatter monodirectional soft radiation from blob I preferentially in the direction opposite to the jet motion. Therefore, gamma-rays, produced in blob II, can be emitted at relatively large angles to the jet axis in the observer’s reference frame. We analyze the basic emission features of such an external blob radiation model. The example modeling of the emission from the FR I type radio galaxy, NGC 1275, is presented.