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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.
Information on the spectral shape of prompt emission in gamma-ray bursts (GRB) is mostly available only at energies $gtrsim10$ keV, where the main instruments for GRB detection are sensitive. The origin of this emission is still very uncertain becaus
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
G. Galanti and M .Roncadelli recently made public some comments on the article by D. Wouters and P. Brun about irregularities induced by photon mixing to axion-like particles in astrophysical media [Phys. Rev. D86, 043005 (2012)]. They claim in parti
The highest-energy blazars exhibit non-thermal radiation extending beyond 1 TeV with high luminosities and strong variabilities, indicating extreme particle acceleration in their relativistic jets. The gamma-ray spectra of blazars contain information
We test different physically motivated models for the spectral shape of the $gamma$-ray emission in a sample of 128 blazars with known redshifts detected by the Fermi Large Area Telescope (LAT) at energies above 50 GeV. The first nine years of LAT da