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

TL;DR

This paper proposes a model where red giant stars interacting with the jets of non-blazar AGN, like M87, produce gamma-ray flares through shock and proton acceleration, explaining observed rapid TeV variability.

Contribution

It introduces a hydrodynamical model of red giant and jet interactions that accounts for fast gamma-ray flares in non-blazar AGN, a novel explanation for observed variability.

Findings

Red giant/jet interactions can produce conditions for proton acceleration.

Such interactions can explain day-scale TeV flares in M87.

Events are likely unbeamed and detectable up to 1 Gpc.

Abstract

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 timescales of a few days. We suggest a scenario of flare gamma-ray emission in non-blazar AGN based on a red giant interacting with the jet at the base. We solve the hydrodynamical equations that describe the evolution of the envelope of a red giant blown by the impact of the jet. 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 events should be mostly detected from non-blazar AGN. They may be frequent phenomena, detectable in the GeV-TeV range even up to distances of $\sim 1$ 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.