Probing acceleration and turbulence at relativistic shocks in blazar jets

Abstract

Diffusive shock acceleration (DSA) at relativistic shocks is widely thought to be an important acceleration mechanism in various astrophysical jet sources, including radio-loud active galactic nuclei such as blazars. Such acceleration can produce the non-thermal particles that emit the broadband continuum radiation that is detected from extragalactic jets. An important recent development for blazar science is the ability of Fermi-LAT spectroscopy to pin down the shape of the distribution of the underlying non-thermal particle population. This paper highlights how multi-wavelength spectra spanning optical to X-ray to gamma-ray bands can be used to probe diffusive acceleration in relativistic, oblique, magnetohydrodynamic (MHD) shocks in blazar jets. Diagnostics on the MHD turbulence near such shocks are obtained using thermal and non-thermal particle distributions resulting from detailed Monte Carlo simulations of DSA. These probes are afforded by the characteristic property that the synchrotron νF ν peak energy does not appear in the gamma-ray band above 100 MeV. We investigate self-consistently the radiative synchrotron and inverse Compton signatures of the simulated particle distributions. Important constraints on the diffusive mean free paths of electrons, and the level of electromagnetic field turbulence are identified for three different case study blazars, Mrk 501, BL Lacertae and AO 0235+164. The X-ray excess of AO 0235+164 in a flare state can be modelled as the signature of bulk Compton scattering of external radiation fields, thereby tightly constraining the energy-dependence of the diffusion coefficient for electrons. The concomitant interpretations that turbulence levels decline with remoteness from jet shocks, and the probable significant role for non-gyroresonant diffusion, are posited.

Physics and Phenomenology of Weakly Magnetized, Relativistic Astrophysical Shock Waves

“…By contrast, the external ultrarelativistic shock that precedes the ejecta of gamma-ray bursts, interacts with a medium of weak magnetization, σ ∼ 10 −9 (for the interstellar medium), possibly as large as 10 −5 in magnetized circumstellar winds, while u sh decreases with time from values as large as 100 − 1000, down to the subrelativistic regime [3]. Inside gamma-ray burst outflows, radio-galaxy and blazar outflows, or even microquasars, internal shocks can occur between layers of material propagating at different four-velocities, triggering mildly relativistic [meaning u sh ∼ O(1)] shock waves, e.g., [16][17][18][19]. In such objects, the magnetization is generally unknown, and may take arbitrarily large or small values.…”

Synchrotron radiation of vector bosons at relativistic colliders

“…Based on this result synchrotron radiation from electromagnetic plasmas was calculated in [14][15][16]. Pair production by a photon in an external magnetic field is a cross channel of the synchrotron radiation.…”

“…It is based on the quasi-classical approximation and allows one to perform explicit summation over the Landau levels yielding rather simple formulas that are convenient in numerical and analytical calculations, see e.g. [16]. While synchrotron radiation of real photons is of great interest in astrophysics, radiation of massive vectors bosons is of interest in heavy-ion collisions and in high intensity laser physics.…”

The VHE SED modelling of Markarian 501 in 2009

“…Here we shall analyze these three different states of Markarian 501 which are given in state [27]. However, for the calculation of these low states, the flaring events during the observation period are excluded from the data.…”