Search for the shortest variability at gamma rays in flat-spectrum radio quasars

TL;DR

This study investigates short-term gamma-ray variability in three flat-spectrum radio quasars, setting new upper limits on variability timescales and suggesting gamma-ray emission originates within the broad-line region.

Contribution

It provides the first constraints on the shortest gamma-ray variability timescales in these quasars, informing models of emission region size and location.

Findings

Upper limits on doubling time scale < 2-3 hours

Gamma-ray emission likely originates inside the broad-line region

First constraints on short-term gamma-ray variability in these sources

Abstract

We report about the search for short-term variability in the high-energy gamma-ray energy band of three flat-spectrum radio quasars (3C 454.3, 3C 273, PKS B1222+216), whose flux at E > 100 MeV exceeded the value of 10^-5 ph cm^-2 s^-1 for at least one day. Although, the statistics was not yet sufficient to effectively measure the characteristic time scale, it allowed us to set tight upper limits on the observed doubling time scale (< 2-3 hours) -- the smallest measured to date at MeV energies --, which can constrain the size of the gamma-ray emitting region. The results obtained in the present work favor the hypothesis that gamma rays are generated inside the broad-line region.