scholarly journals MULTIWAVELENGTH PROBES OF THE ENVIRONS OF RELATIVISTIC SHOCKS IN BLAZAR JETS

2014 ◽  
Vol 28 ◽  
pp. 1460167 ◽  
Author(s):  
MATTHEW G. BARING ◽  
MARKUS BÖTTCHER ◽  
ERROL J. SUMMERLIN
Keyword(s):  
Gamma Ray ◽  
Mean Free Path ◽  
High Energy ◽  
Shock Acceleration ◽  
Diffusive Shock Acceleration ◽  
Particle Distributions ◽  
Astrophysical Jet ◽  
Relativistic Shocks ◽  
Diagnostic Potential ◽  
Power Law Index

Diffusive shock acceleration (DSA) at relativistic shocks is likely to be an important acceleration mechanism in various astrophysical jet sources, including radio-loud AGN. An important recent development for blazar science is the ability of Fermi-LAT data to pin down the power-law index of the high energy portion of emission in these sources, and therefore also the index of the underlying non-thermal particle population. This diagnostic potential was not possible prior to Fermi launch, when gamma-ray information was dominated by the highly-absorbed TeV band. This paper highlights how multiwavelength spectra including X-ray band and Fermi data can be used to probe diffusive acceleration in relativistic, oblique, MHD shocks in blazar jets. The spectral index of the non-thermal particle distributions resulting from Monte Carlo simulations of DSA, and the fraction of thermal particles accelerated to non-thermal energies, depend sensitively on the particles' mean free path scale, and also on the magnetic field obliquity to the shock normal. We investigate self-consistently the radiative synchrotron/Compton signatures of the resulting thermal and non-thermal particle distributions. Important constraints on the frequency of particle scattering and the level of field turbulence are identified for the blazar AO 0235+164. The possible interpretation that turbulence levels decline with remoteness from jet shocks, and a significant role for non-gyroresonant diffusion, are discussed.

scholarly journals A Shock-in-Jet Synchrotron Mirror Model for Blazars

Physics ◽  
2021 ◽  
Vol 3 (4) ◽  
pp. 1112-1122
Author(s):  
Markus Böttcher
Keyword(s):  
Synchrotron Radiation ◽  
Gamma Ray ◽  
Low Frequency ◽  
High Energy ◽  
Shock Acceleration ◽  
Additional Parameter ◽  
Diffusive Shock Acceleration ◽  
Spectral Variability ◽  
Particle Distributions ◽  
Self Consistent

Reinhard Schlickeiser has made groundbreaking contributions to various aspects of blazar physics, including diffusive shock acceleration, the theory of synchrotron radiation, the production of gamma-rays through Compton scattering in various astrophysical sources, etc. This paper, describing the development of a self-consistent shock-in-jet model for blazars with a synchrotron mirror feature, is therefore an appropriate contribution to a Special Issue in honor of Reinhard Schlickeiser’s 70th birthday. The model is based on our previous development of a self-consistent shock-in-jet model with relativistic thermal and non-thermal particle distributions evaluated via Monte-Carlo simulations of diffusive shock acceleration, and time-dependent radiative transport. This model has been very successful in modeling spectral variability patterns of several blazars, but has difficulties describing orphan flares, i.e., high-energy flares without a significant counterpart in the low-frequency (synchrotron) radiation component. As a solution, this paper investigates the possibility of a synchrotron mirror component within the shock-in-jet model. It is demonstrated that orphan flares result naturally in this scenario. The model’s applicability to a recently observed orphan gamma-ray flare in the blazar 3C279 is discussed and it is found that only orphan flares with mild (≲ a factor of 2–3) enhancements of the Compton dominance can be reproduced in a synchrotron-mirror scenario, if no additional parameter changes are invoked.

scholarly journals Spectral and Polarization Signatures of Relativistic Shocks in Blazars

2016 ◽  
Author(s):  
Markus Boettcher
Keyword(s):  
Pitch Angle ◽  
High Energy ◽  
Shock Acceleration ◽  
Spectral Energy ◽  
Polarization Angle ◽  
Proton Synchrotron ◽  
Diffusive Shock Acceleration ◽  
X Ray ◽  
Relativistic Shocks ◽  
Multi Wavelength

Relativistic shocks are one of the most plausible sites of the emission of strongly variable, polarized multi-wavelength emission from relativistic jet sources such as blazars, via diffusive shock acceleration (DSA) of relativistic particles. This paper summarizes recent results on a self-consistent coupling of diffusive shock acceleration and radiation transfer in blazar jets. We demonstrate that the observed spectral energy distributions (SEDs) of blazars strongly constrain the nature of hydromagnetic turbulence responsible for pitch-angle scattering by requiring a strongly energy-dependent pitch-angle mean free path. The prominent soft X-ray excess (``Big Blue Bump'') in the SED of the BL Lac object AO 0235+164 can be modelled as the signature of bulk Compton scattering of external radiation fields by the thermal electron population, which places additional constraints on the level of hydromagnetic turbulence. It has further been demonstrated that internal shocks propagating in a jet pervaded by a helical magnetic field naturally produce polarization-angle swings by 180$^o$, in tandem with multi-wavelength flaring activity, without requiring any helical motion paths or other asymmetric jet structures. The specific application of this model to 3C279 presents the first consistent, simultaneous modeling of snap-shot SEDs, multi-wavelength light curves and time-dependent polarization signatures of a blazar during a polarization-angle (PA) rotation. This model has recently been generalized to a lepto-hadronic model, in which the high-energy emission is dominated by proton synchrotron radiation. It is shown that in this case, the high-energy (X-ray and $\gamma$-ray) polarization signatures are expected to be significantly more stable (not showing PA rotations) than the low-energy (electron-synchrotron) signatures.

scholarly journals Active Galactic Nuclei: Jets as the Source of Hadrons and Neutrinos

2014 ◽  
Vol 1 (1) ◽  
pp. 269-273
Author(s):  
Athina Meli ◽  
Paolo Ciarcelluti
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
Cosmic Ray ◽  
High Energy ◽  
Plasma Jets ◽  
Shock Acceleration ◽  
Fermi Acceleration ◽  
Acceleration Mechanism ◽  
Relativistic Shocks

Active galactic nuclei are extragalactic sources, and their relativistic hot-plasma jets are believed to be the main candidates of the cosmic-ray origin, above the so-called knee region of the cosmic-ray spectrum. Relativistic shocks, either single or multiple, have been observed or been theorized to be forming within relativistic jet channels in almost all active galactic nuclei sources. The acceleration of non-thermal particles (e.g. electrons, protons) via the shock Fermi acceleration mechanism, is believed to be mainly responsible for the power-law energy distribution of the observed cosmic-rays, which in very high energies can consequently radiate high energy gamma-rays and neutrinos, through related radiation channels. Here, we will focus on the primary particle (hadronic) shock acceleration mechanism, and we will present a comparative simulation study of the properties of single and multiple relativistic shocks, which occur in AGN jets. We will show that the role of relativistic (quasi-parallel either quasi-perpendicular) shocks, is quite important since it can dramatically alter the primary CR spectral indices and acceleration eciencies. These properties being carried onto gamma-ray and neutrino radiation characteristics, makes the combination of them a quite appealing theme for relativistic plasma and shock acceleration physics, as well as observational cosmic-ray, gamma-ray and neutrino astronomy.

scholarly journals Diagnosing particle acceleration in relativistic jets

2014 ◽  
Vol 10 (S313) ◽  
pp. 153-158
Author(s):  
Markus Böttcher ◽  
Matthew G. Baring ◽  
Edison P. Liang ◽  
Errol J. Summerlin ◽  
Wen Fu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Particle Acceleration ◽  
Lorentz Factor ◽  
High Energy ◽  
Shock Acceleration ◽  
Relativistic Jets ◽  
Diffusive Shock Acceleration ◽  
Magnetic Field Generation ◽  
Particle Distributions ◽  
Particle In Cell

AbstractThe high-energy emission from blazars and other relativistic jet sources indicates that electrons are accelerated to ultra-relativistic (GeV - TeV) energies in these systems. This paper summarizes recent results from numerical studies of two fundamentally different particle acceleration mechanisms potentially at work in relativistic jets: Magnetic-field generation and relativistic particle acceleration in relativistic shear layers, which are likely to be present in relativistic jets, is studied via Particle-in-Cell (PIC) simulations. Diffusive shock acceleration at relativistic shocks is investigated using Monte-Carlo simulations. The resulting magnetic-field configurations and thermal + non-thermal particle distributions are then used to predict multi-wavelength radiative (synchrotron + Compton) signatures of both acceleration scenarios. In particular, we address how anisotropic shear-layer acceleration may be able to circumvent the well-known Lorentz-factor crisis, and how the self-consistent evaluation of thermal + non-thermal particle populations in diffusive shock acceleration simulations provides tests of the bulk Comptonization model for the Big Blue Bump observed in the SEDs of several blazars.

scholarly journals Extragalactic shocks as cosmic accelerators

2006 ◽  
Vol 2 (14) ◽  
pp. 95-96
Author(s):  
Mikhail V. Medvedev
Keyword(s):  
Active Galactic Nuclei ◽  
Large Scale ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
High Energy ◽  
Maximum Energy ◽  
Shock Acceleration ◽  
Fermi Acceleration ◽  
High Energy Cosmic Rays ◽  
Relativistic Shocks

AbstractIt is quite well established that shocks accelerate particles via the Fermi mechanism. We discuss common features of various extragalactic sources, ranging from Gamma-Ray Bursts and jets of Active Galactic Nuclei to Large-Scale Structure shocks and address how they affect particle acceleration. In particular, we address constraints on the maximum energy of ultra-high-energy cosmic rays. Interestingly, some recent studies indicate that Fermi acceleration in relativistic shocks (and GRBs, in particular) faces severe difficulties. We will address this issue and demonstrate that the ‘observed’ shock acceleration of electrons may have nothing to do with Fermi acceleration, but may rather be associated with micro-physics of collisionless shocks.

scholarly journals Hybrid modeling of diffusive shock acceleration in collisionless shocks in multispecies plasma

2018 ◽  
pp. 373-378
Author(s):  
J. A. Kropotina ◽  
A. M. Bykov ◽  
V. E. Ermolina ◽  
S. M. Osipov ◽  
V. I. Romansky
Keyword(s):  
Heavy Ions ◽  
Supernova Remnants ◽  
Gamma Ray ◽  
Hydrogen Plasma ◽  
High Energy ◽  
Shock Acceleration ◽  
High Energy Particle ◽  
Diffusive Shock Acceleration ◽  
Particle Injection ◽  
Initial Flow

Diffusive shock acceleration (DSA) is a very efficient mechanism of high energy particle acceleration in heliosphere, supernova remnants, stellar winds and gamma-ray bursts. We present microscopic simulation of particle injection and diffusive shock acceleration which is performed with 3D divergence-conserving second-order accurate hybrid code "Maximus". Hydrogen plasma with admixture of various heavy ions is considered. The injection process is found to start through shock reflection for both hydrogen and heavier ions. However, the reflection process depends on charge-to-mass ratio. While hydrogen ions reflection appears at shock ramp and is governed by the cross-shock potential, the reflection of ions with greater A=Z proceeds deeper down-stream via gyration in perpendicular magnetic field component. The heavy ions appear to inject into the DSA preferentially, but this chemical enhancement saturates with growing A=Z. The protons injection efficiency is estimated within various approaches, and it is shown that about 20% of initial flow energy goes into accelerated particles.

A NEW MECHANISM FOR PARTICLE ACCELERATION IN RELATIVISTIC JETS

2008 ◽  
Vol 17 (10) ◽  
pp. 1839-1847 ◽  
Author(s):  
E. V. DERISHEV ◽  
F. A. AHARONIAN ◽  
V. V. KOCHAROVSKY ◽  
Vl. V. KOCHAROVSKY
Keyword(s):  
Gamma Ray ◽  
Cosmic Ray ◽  
Nucleon Nucleon ◽  
Gain Factor ◽  
Shock Acceleration ◽  
Opening Angle ◽  
Relativistic Jets ◽  
Diffusive Shock Acceleration ◽  
Radiation Beam ◽  
Relativistic Shocks

We compare different acceleration mechanisms in application to relativistic jets and show that the converter mechanism, suggested recently, is the least sensitive to the geometry of the magnetic field in accelerators, and can routinely operate up to cosmic-ray energies close to the fundamental limit. The converter mechanism utilizes multiple conversions of charged particles into neutral ones (protons to neutrons and electrons/positrons to photons) and back by means of photon-induced reactions or inelastic nucleon-nucleon collisions. It works efficiently both in relativistic shocks and in shear flows under the conditions typical for active galactic nuclei, gamma-ray bursts, and microquasars, where it often outperforms the standard diffusive shock acceleration. The main advantages of the converter mechanism in such environments are that it greatly diminishes particle losses downstream and avoids the reduction in the energy gain factor, which normally takes place due to the highly collimated distribution of accelerated particles. We also discuss the properties of gamma-ray radiation, which accompanies acceleration of cosmic rays via the converter mechanism and can provide evidence for the latter. In particular, we point out that the opening angle of the radiation beam-pattern is different at different photon energies, which is relevant to the observability of gamma-ray sources as well as to their timing properties.

scholarly journals Particle Acceleration in High-Energy Gamma-Ray Sources

1994 ◽  
Vol 142 ◽  
pp. 877-881
Author(s):  
David Eichler
Keyword(s):  
Gamma Rays ◽  
Production Efficiency ◽  
Gamma Ray ◽  
High Energy ◽  
Thick Target ◽  
Shock Acceleration ◽  
High Production Efficiency ◽  
Energy Gamma ◽  
High Production ◽  
High Energy Particles

AbstractMany proficient gamma-ray sources show energy spectra that are consistent with E−2 primary spectra. Such sources include recently identified gamma-ray quasars and some gamma-ray bursts. Assuming thick target conversion, this is consistent with shock acceleration, and the dominance of the gamma rays of the luminosity is also consistent with previous predictions of high production efficiency of fresh cosmic rays in shocks. The spectral cutoffs in the gamma rays may offer clues as to whether the high-energy particles are electrons or protons. Resolution of this matter might have implications for the nature of the sources and for theory of shock accelerated electrons.Subject headings: acceleration of particles — gamma rays: bursts — shock waves

Gamma-Ray Solar Flares and In Situ Particle Acceleration

2017 ◽  
Vol 13 (S335) ◽  
pp. 43-48 ◽  
Author(s):  
Alexei Struminsky
Keyword(s):  
Gamma Ray ◽  
Solar Energetic Particle ◽  
High Energy ◽  
Shock Acceleration ◽  
Relative Role ◽  
Energy Gamma ◽  
Mass Ejection ◽  
Flare Site

AbstractAt present two concurrent paradigms of solar energetic particle (SEP) origin exist: acceleration directly in the flare site or by the shock wave of coronal mass ejection (CME). Active discussions on a relative role of flares and coronal mass ejections for SEP acceleration and propagation are continuous until now. In my opinion only future observations of solar high energy γ–emission with better spectral, spatial and temporal resolution may clarify this issue. In my report I discuss possible signatures of the flare and shock acceleration processes. What is a picture provided by the current instruments? What can we expect to observe with a perfect instrument in high energy gamma rays in one or another case on a time scale of impulsive and long decay flare phases?

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