Magnetic field amplification and flat spectrum radio quasars

Abstract

We perform time-dependent, spatially-resolved simulations of blazar emission to evaluate several flaring scenarios related to magnetic-field amplification and enhanced particle acceleration. The code explicitly accounts for light-travel-time effects and is applied to flares observed in the flat spectrum radio quasar (FSRQ) PKS 0208-512, which show optical/γ-ray correlation at some times, but orphan optical flares at other times. Changes in both the magnetic field and the particle acceleration efficiency are explored as causes of flares. Generally, external Compton emission appears to describe the available data better than a synchrotron self-Compton scenario, and in particular orphan optical flares are difficult to produce in the SSC framework. X-ray soft-excesses, γ-ray spectral hardening, and the detections at very high energies of certain FSRQs during flares find natural explanations in the EC scenario with particle acceleration change. Likewise, optical flares with/without γ-ray counterparts can be explained by different allocations of energy between the magnetization and particle acceleration, which may be related to the orientation of the magnetic field relative to the jet flow. We also calculate the degree of linear polarization and polarization angle as a function of time for a jet with helical magnetic field. Tightening of the magnetic helix immediately downstream of the jet perturbations, where flares occur, can be sufficient to explain the increases in the degree of polarization and a rotation by 180 • of the observed polarization angle, if light-travel-time effects are properly considered.

Particle diffusion and localized acceleration in inhomogeneous AGN jets – II. Stochastic variation

“…That extra time is typically a fraction of the light-crossing time of the emis-sion region, which is roughly 10 ks in terms of delay in the observed signal in our current cases. This 'fraction' turns out to be ∼ 0.4 in a case where the high-energy electrons are homogeneously distributed and do not cool significantly (Chen et al 2014a). In the current case where acceleration-diffusion causes the emission region to be dominated by its central portion, this fraction is likely much smaller, and so is the impact of internal LTTEs.…”

Radiation and Polarization Signatures of the 3d Multizone Time-Dependent Hadronic Blazar Model

“…The development of time-dependent leptonic models has been quite fruitful (e.g., Joshi & Böttcher 2011;Diltz & Böttcher 2014;Weidinger & Spanier 2015;Asano & Hayashida 2015). Although one-zone leptonic models sometimes have difficulty in explaining the frequently seen symmetric light curves, some multi-zone leptonic models that explicitly include the light travel time effects (LTTEs) have successfully resolved that issue (e.g., Chen et al 2014). On the other hand, due to the more complicated cascading processes, hadronic models are generally stationary and/or single-zone (e.g., Mastichiadis & Kirk 1995;Cerruti et al 2015;Yan & Zhang 2015).…”

A Steady-state Spectral Model for Electron Acceleration and Cooling in Blazar Jets: Application to 3C 279

“…The Diltz & Böttcher (2014) model fits their sample dataset well, and they are able to conclude that a decrease in the overall acceleration timescale is related to a correlation between the optical and γ-ray bands, which was observed during several 3C 279 flares. Chen et al (2014) used a multizone inhomogeneous and time-dependent model to investigate FSRQ emission regions. They implement continuous stochastic acceleration, radiative cooling, particle escape, and the injection of a pre-accelerated electron distribution.…”

“…Models that do not include shock acceleration explicitly usually assume that the injected electrons are preaccelerated (e.g. Tramacere et al 2011;Diltz & Böttcher 2014;Chen et al 2014;Asano & Hayashida 2015). In contrast, we do not assume particle pre-acceleration, and instead treat all acceleration processes explicitly using the transport equation.…”