Measuring parameters of AGN central engines with very high energy gamma-ray flares

TL;DR

This paper presents a model linking very high energy gamma-ray variability in blazars to the properties of the central supermassive black hole, using observed flare data to constrain black hole parameters.

Contribution

It introduces a compact source model that connects gamma-ray variability with black hole mass and spin, providing a new method to measure AGN central engine parameters.

Findings

Variability timescales constrain black hole mass.

Recurrence of sub-flares relates to black hole angular momentum.

Model applied to PKS 2155-304 to estimate black hole properties.

Abstract

We discuss a "compact source" model of very high energy (VHE) emission from blazars in which the variability time is determined by the blazar central engine. In this model electron or proton acceleration close to the supermassive black hole is followed by the development of electromagnetic cascade in a radiatively inefficient accretion flow. Assuming such a model for the TeV blazar PKS 2155-304, we show that the variability properties of the TeV gamma-ray signal observed during a bright flare from this source, such as the minimal variability time scale and the recurrence period of the sub-flares, constrain the mass and the angular momentum of the supermassive black hole.