Two blobs in a jet model for the gamma-ray emission in radio galaxies

TL;DR

This paper proposes a two-blob model in radio galaxy jets to explain observed high-energy gamma-ray emissions at large angles from the jet axis, involving distinct emission regions with different Lorentz factors.

Contribution

It introduces a novel two-blob scenario with different Lorentz factors to account for gamma-ray emissions at large angles in radio galaxies.

Findings

Model successfully explains gamma-ray emission at large angles.

Application to NGC 1275 demonstrates the model's viability.

Provides insights into jet structure and emission mechanisms.

Abstract

In the unified scheme FR I type radio galaxies are identified with the blazar type active galaxies 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 which 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 up-scatter mono-directional soft radiation from the blob I preferentially in the direction opposite to the jet motion. Therefore, gamma-rays, produced in the blob II, can be emitted at a relatively large angles to the jet axis in the observer's reference frame. We analyze the basic emission features of such external blob radiation model. The example modeling of the emission from the FR I type radio galaxy, NGC 1275, is presented.