Turbulent spectra of the brightest gamma-ray flares of blazars

TL;DR

This study analyzes the spectral properties of bright gamma-ray flares in blazars, revealing significant spectral variability and suggesting particle acceleration occurs in turbulent environments, with implications for understanding emission mechanisms.

Contribution

It provides the first detailed analysis of spectral breaks and curvature in bright blazar flares, highlighting the role of turbulence in particle acceleration.

Findings

Less than half of flares show spectral breaks with no regular patterns.

Short-duration flares often have strong spectral curvature with peaks above 100 MeV.

Spectral variability indicates temporal fluctuations in particle energy distributions.

Abstract

We investigate the spectral properties of the brightest gamma-ray flares of blazars detected by the Fermi Large Area Telescope. We search for the presence of spectral breaks and measure the spectral curvature on typical time scales of a few days. We identify significant spectral breaks in fewer than half of the analyzed flares, but their parameters do not show any discernible regularities, and in particular there is no indication for gamma-ray absorption at any fixed source-frame photon energy. More interestingly, we find that the studied blazars are characterized by significant spectral variability. Gamma-ray flares of short duration are often characterized by strong spectral curvature, with the spectral peak located above 100 MeV. Since these spectral variations are observed despite excellent photon statistics, they must reflect temporal fluctuations in the energy distributions of the emitting particles. We suggest that highly regular gamma-ray spectra of blazars integrated over long time scales emerge from a superposition of many short-lived irregular components with relatively narrow spectra. This would imply that the emitting particles are accelerated in strongly turbulent environments.