Suborbital Fermi/LAT Analysis of the Brightest Gamma-Ray Flare of Blazar 3C 454.3

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 (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 ~5h, which is consistent with the standard blazar models.Comment: 8 pages, 4 figures, special issue "Microvariability of Blazars", Ed. James R. Web

A Model of Polarisation Rotations in Blazars from Kink Instabilities in Relativistic Jets

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.Comment: 6 pages, 3 figures; Proceedings of the conference "Polarised Emission from Astrophysical Jets", 12-16 June 2017, Ierapetra, Greece; Eds. M. Boettcher, E. Angelakis and J. L. G\'{o}me

The sequence of Compton dominance in blazars based on data from WISE and Fermi/LAT

The two-component broad-band spectral energy distributions of blazars were suggested to form a sequence in which (1) the peak frequency of the low-energy (synchrotron) component nu_syn is anticorrelated with the synchrotron luminosity L_syn, and (2) the luminosity ratio of the high-energy (inverse Compton) to synchrotron components q = L_IC / L_syn (Compton dominance) increases with L_syn from the BL Lac objects (BL Lacs) to the flat spectrum radio quasars (FSRQs). The Compton dominance parameter is an important probe of plasma magnetisation in the blazar zones within relativistic jets. We investigate a sample of blazars detected by WISE in the mid-infrared (MIR) band and by Fermi/LAT in the GeV gamma-ray band, with the focus on the distribution of luminosities and photon indices. Our findings are the following: (1) the MIR photon index Gamma_W12 is a useful probe of the blazar sequence, with the exception of low-luminosity BL Lacs that are most likely contaminated by their host galaxies (L_W1 ~ 10^44 erg/s and Gamma_W12 < 1); (2) Gamma_W12 is correlated with the gamma-ray photon index Gamma_1-100GeV, with the MIR luminosity L_W1, and with the Fermi/WISE Compton dominance q_FW = L_1GeV/L_W1; (3) a clean separation between FSRQs and BL Lacs can be seen in the parameter space of Gamma_W12 and q_FW; (4) the observed distribution of MIR luminosity L_W1 vs. Compton dominance q_FW for the entire sample of blazars can be modeled as a sequence of lepto-magnetic jet powers in the range (log_10 P_eB) in [42:45] with the preference for sub-equipartition magnetic fields P_B/P_e in [0.05:1], assuming fixed bulk Lorentz factor Gamma_j = 15, fixed jet opening angle Gamma_j Theta_j = 0.3, fixed radiative efficiency of jet electrons epsilon_em = 50%, and that external radiation luminosity scales like L_ext propto (P_eB)^(1.6) (parameter degeneracies are discussed).Comment: 9 pages, 5 figures, submitted to A&

Kinetic simulations of relativistic magnetic reconnection with synchrotron and inverse Compton cooling

First results are presented from kinetic numerical simulations of relativistic collisionless magnetic reconnection in pair plasma that include radiation reaction from both synchrotron and inverse Compton (IC) processes, motivated by non-thermal high-energy astrophysical sources, including in particular blazars. These simulations are initiated from a configuration known as 'ABC fields' that evolves due to coalescence instability and generates thin current layers in its linear phase. Global radiative efficiencies, instability growth rates, time-dependent radiation spectra, lightcurves, variability statistics and the structure of current layers are investigated for a broad range of initial parameters. We find that the IC radiative signatures are generally similar to the synchrotron signatures. The luminosity ratio of IC to synchrotron spectral components, the Compton dominance, can be modified by more than one order of magnitude with respect to its nominal value. For very short cooling lengths, we find evidence for modification of the temperature profile across the current layers, no systematic compression of plasma density, and very consistent profiles of E.B. We decompose the profiles of E.B with the use of the Vlasov momentum equation, demonstrating a contribution from radiation reaction at the thickness scale consistent with the temperature profile.Comment: 18 pages, 6 figures, accepted for publication in the Journal of Plasma Physics, special collection "Plasma physics under extreme conditions: from high-energy-density experiments to astrophysics", Eds. F. Fiuza, R. D. Blandford & S. Glenze