Gamma-ray flares from red-giant-jet interactions in AGN

Non-blazar AGN have been recently established as a class of gamma-ray sources. M87, a nearby representative of this class, show fast TeV variability on time scales of a few days. Here it is suggested a scenario of flare gamma-ray emission in non-blazar AGN based on a red giant interacting with the jet at the base. The hydrodynamical equations that describe the evolution of the envelope of a red giant blown by the impact of the jet, are solved. If the red giant is at least slightly tidally disrupted by the supermassive black hole, enough stellar material will be blown by the jet, expanding quickly until a significant part of the jet is shocked. This process can render suitable conditions for energy dissipation and proton acceleration, which could explain the detected day-scale TeV flares from M87 via proton-proton collisions. Since the produced radiation would be unbeamed, such an event should be mostly detected from non-blazar AGN. They may be frequent phenomena, detectable in the GeV-TeV range even up to distances of ∼1 Gpc for the most powerful jets. The counterparts at lower energies are expected to be not too bright. M87, and nearby non-blazar AGN in general, can be fast variable sources of gamma rays through red-giant-jet interactions.