Ultimate synchrotron cutoff in gamma-ray spectra of blazars as a signature of the converter mechanism

TL;DR

This paper investigates the maximum energy of synchrotron radiation in blazar jets, proposing that a cutoff or dip in spectra caused by the converter mechanism can serve as a signature, with numerical simulations supporting this idea.

Contribution

It introduces the concept of an ultimate synchrotron cutoff as a signature of the converter mechanism in blazar spectra, supported by numerical simulations and comparison with observational data.

Findings

The synchrotron cutoff can appear in blazar spectra due to the converter mechanism.

Numerical simulations reproduce spectral variations based on source luminosity and emission site scale.

Comparison with EGRET data suggests possible but not statistically significant agreement.

Abstract

There is a robust upper limit on the energy of synchrotron radiation in high-energy astrophysics: $ \sim m_{\rm e} c^2 /\alpha$, where $\alpha = 1/137$ is the fine structure constant and the value refers to the comoving frame of the fluid. This is the maximal energy of synchrotron photons which can be emitted by an electron having an arbitrarily high initial energy after it turns by angle $\sim \pi$ in the magnetic field. This upper limit can be naturally reached if the converter mechanism contributes to the jet radiation and can be imprinted in spectra of some blazars as a cutoff or a dip in the GeV range. We use numerical simulations to probe the range of parameters of a radiating jet where the ultimate synchrotron cutoff appears. We reproduce the variety of spectra depending on the source luminosity and on the scale of the emission site. We also compare our results with the EGRET blazar spectra in order to illustrate that agreement is possible but still not statistically significant. The predicted feature, if it exists, should be observed by {\it Fermi} in spectra of some blazars.