Description: Galaxies, Vol. 5, Pages 100: Suborbital Fermi/LAT Analysis of the Brightest Gamma-Ray Flare of Blazar 3C 454.3 Galaxies doi: 10.3390/galaxies5040100 Authors: Krzysztof Nalewajko Recent detection of suborbital gamma-ray variability of Flat Spectrum Radio Quasar (FSRQ) 3C 279 by Fermi Large Area Telescope (LAT) is in severe conflict with established models of blazar emission. This paper presents the results of suborbital analysis of the Fermi/LAT data for the brightest gamma-ray flare of another FSRQ blazar 3C 454.3 in November 2010 (Modified Julian Date; MJD 55516-22). Gamma-ray light curves are calculated for characteristic time bin lengths as short as 3 min. The measured variations of the 0.1–10 GeV photon flux are tested against the hypothesis of steady intraorbit flux. In addition, the structure function is calculated for absolute photon flux differences and for their significances. Significant gamma-ray flux variations are measured only over time scales longer than ∼5 h, which is consistent with the standard blazar models.

Description: Galaxies, Vol. 5, Pages 64: A Model of Polarisation Rotations in Blazars from Kink Instabilities in Relativistic Jets Galaxies doi: 10.3390/galaxies5040064 Authors: Krzysztof Nalewajko This paper presents a simple model of polarisation rotation in optically thin relativistic jets of blazars. The model is based on the development of helical (kink) mode of current-driven instability. A possible explanation is suggested for the observational connection between polarisation rotations and optical/gamma-ray flares in blazars, if the current-driven modes are triggered by secular increases of the total jet power. The importance of intrinsic depolarisation in limiting the amplitude of coherent polarisation rotations is demonstrated. The polarisation rotation amplitude is thus very sensitive to the viewing angle, which appears to be inconsistent with the observational estimates of viewing angles in blazars showing polarisation rotations. Overall, there are serious obstacles to explaining large-amplitude polarisation rotations in blazars in terms of current-driven kink modes.

Description: Rapid and luminous flares of non-thermal radiation observed in blazars require an efficient mechanism of energy dissipation and particle acceleration in relativistic active galactic nuclei (AGN) jets. Particle acceleration in relativistic magnetic reconnection is being actively studied by kinetic numerical simulations. Relativistic reconnection produces hard power-law electron energy distributions N ( γ ) ∝ γ − p exp ( − γ / γ max ) with index p → 1 and exponential cut-off Lorentz factor γ max ∼ σ in the limit of magnetization σ = B 2 / ( 4 π w ) ≫ 1 (where w is the relativistic enthalpy density). Reconnection in electron-proton plasma can additionally boost γ max by the mass ratio m p / m e . Hence, in order to accelerate particles to γ max ∼ 10 6 in the case of BL Lacs, reconnection should proceed in plasma of very high magnetization σ max ≳ 10 3 . On the other hand, moderate mean jet magnetization values are required for magnetic bulk acceleration of relativistic jets, σ mean ∼ Γ j ≲ 20 (where Γ j is the jet bulk Lorentz factor). I propose that the systematic dependence of γ max on blazar luminosity class—the blazar sequence—may result from a systematic trend in σ max due to homogeneous loading of leptons by pair creation regulated by the energy density of high-energy external radiation fields. At the same time, relativistic AGN jets should be highly inhomogeneous due to filamentary loading of protons, which should determine the value of σ mean roughly independently of the blazar class.