Star-Jet Interactions and Gamma-Ray Outbursts from 3c454.3

TL;DR

This paper presents a model explaining the gamma-ray flares from blazar 3c454.3 through jet-star interactions, detailing the evolution of stellar material within the jet and its radiation, matching observed flare characteristics.

Contribution

The study introduces a novel jet-star interaction model for gamma-ray flares, including analytical treatment of stellar envelope evolution and radiation, with constraints on black hole mass and jet power.

Findings

Explains day-long gamma-ray flares with hour-scale variability.

Constrains black hole mass to approximately 10^9 solar masses.

Suggests proton synchrotron radiation as a potential emission mechanism.

Abstract

We propose a model to explain the ultra-bright GeV gamma-ray flares observed from the blazar \c454. The model is based on the concept of a relativistic jet interacting with compact gas condensations produced when a star (red giant) crosses the jet close to the central black hole. The study includes an analytical treatment of the evolution of the envelop lost by the star within the jet, and calculations of the related high-energy radiation. The model readily explains the day-long, variable on timescales of hours, GeV gamma-ray flare from \c454, observed during November 2010 on top of a weeks-long plateau. In the proposed scenario, the plateau state is caused by a strong wind generated by the heating of the star atmosphere by nonthermal particles accelerated at the jet-star interaction region. The flare itself could be produced by a few clouds of matter lost by the red giant after the initial impact of the jet. In the framework of the proposed scenario, the observations constrain the key model parameters of the source, including the mass of the central black hole: $M_{\rm BH}\simeq 10^9 M_{\odot}$, the total jet power: $L_{\rm j}\simeq 10^{48}\,\rm erg\,s^{-1}$, and the Doppler factor of the gamma-ray emitting clouds, $\delta\simeq 20$. Whereas we do not specify the particle acceleration mechanisms, the potential gamma-ray production processes are discussed and compared in the context of the proposed model. We argue that synchrotron radiation of protons has certain advantages compared to other radiation channels of directly accelerated electrons.