Variability of gamma-ray emission from blazars on the black hole timescales

TL;DR

This study analyzes gamma-ray variability in blazars using Fermi/LAT data, revealing that their minimal variability timescales are often linked to the black hole's properties, suggesting processes near the supermassive black hole influence gamma-ray emission.

Contribution

It provides new insights into the minimal variability timescales of blazars and their connection to the central black hole, highlighting the influence of black hole physics on gamma-ray emission.

Findings

Blazars show variability down to the minimal timescale resolvable by Fermi.

Minimal variability timescales often approach those associated with the black hole.

No variability shorter than the black hole horizon crossing time was observed.

Abstract

We investigate the variability properties of blazars in the GeV band using the data of the Fermi/LAT telescope. We find that blazars exhibit variability on the scales down to the minimal timescale resolvable by Fermi, which is a function of the peak photon count rate in the LAT. This implies that the real minimal variability timescales for the majority of blazars are typically shorter than those resolvable by the LAT. We find that for several blazars these minimal variability timescales reach those associated to the blazar central engine, the supermassive black hole. At the same time, none of the blazars exhibits variability on the timescale shorter than the black hole horizon light crossing time and/or the period of rotation around the last stable circular orbit. Based on this fact, we argue that the timing properties of the gamma-ray signal could be determined by the processes in the direct vicinity of the supermassive black hole.