Multiwavelength Variability Signatures of Relativistic Shocks in Blazar Jets

TL;DR

This paper models multiwavelength variability in blazar jets by simulating relativistic shocks with a two-zone, time-dependent approach, revealing how shock acceleration and cooling produce observable spectral and temporal signatures.

Contribution

It extends previous one-zone models by including full time dependence and a two-zone structure, improving the understanding of blazar flare variability and spectral features.

Findings

Predicted correlated multiwavelength variability with specific time lags.

Identified spectral hysteresis patterns across wavebands.

Fitted observed SEDs and light curves of 3C 279 and studied flaring in Mrk 501.

Abstract

Mildly-relativistic shocks that are embedded in colliding magnetohydrodynamic flows are prime sites for relativistic particle acceleration and production of strongly variable, polarized multi-wavelength emission from relativistic jet sources such as blazars and gamma-ray bursts. The principal energization mechanisms at these shocks are diffusive shock acceleration and shock drift acceleration. In recent work, we had self-consistently coupled shock acceleration and radiation transfer simulations in blazar jets in a basic one-zone scenario. These one-zone models revealed that the observed spectral energy distributions (SEDs) of blazars strongly constrain the nature of the shock layer hydromagnetic turbulence. In this paper, we expand our previous work by including full time dependence and treating two zones, one being the site of acceleration, and the second being a larger emission zone. This construction is applied to multiwavelength flares of the flat spectrum radio quasar 3C 279, fitting snap-shot SEDs and generating light curves that are consistent with observed variability timescales. We also present a generic study for the typical flaring behavior of the BL Lac object Mrk 501. The model predicts correlated variability across all wavebands, but cross-band time lags depending on the type of blazar (FSRQ vs. BL Lac), as well as distinctive spectral hysteresis patterns in all wavelength bands, from mm radio waves to gamma-rays. These evolutionary signatures serve to provide diagnostics on the competition between acceleration and radiative cooling.