Constraining the location of the emitting region in Fermi blazars through rapid gamma-ray variability

TL;DR

This study analyzes Fermi LAT light curves of blazars 3C 454.3 and PKS 1510-089, revealing rapid gamma-ray variability on hours timescales that constrains the location of the emission region closer to the black hole than previously thought.

Contribution

It provides new evidence that gamma-ray emission in blazars occurs in regions nearer to the black hole, challenging models placing the emission at large distances.

Findings

Detected variability on timescales of a few hours.

Challenged the model of distant gamma-ray emission regions.

Provided constraints on the emission site location.

Abstract

We consider the 1.5 years Fermi Large Area Telescope light curves (E > 100 MeV) of the flat spectrum radio quasars 3C 454.3 and PKS 1510-089, which show high activity in this period of time. We characterise the duty cycle of the source by comparing the time spent by the sources at different flux levels. We consider in detail the light curves covering periods of extreme flux. The large number of high-energy photons collected by LAT in these events allows us to find evidence of variability on timescales of few hours. We discuss the implications of significant variability on such short timescales, that challenge the scenario recently advanced in which the bulk of the gamma-ray luminosity is produced in regions of the jet at large distances (tens of parsec) from the black hole.