scholarly journals Radiation from accelerated particles in shocks

2011 ◽  
Vol 7 (S279) ◽  
pp. 371-372
Author(s):  
K.-I. Nishikawa ◽  
B. Zhang ◽  
E. J. Choi ◽  
K. W. Min ◽  
J. Niemiec ◽  
...  
Keyword(s):  
Particle Acceleration ◽  
Magnetic Fields ◽  
Supernova Remnants ◽  
Gamma Ray ◽  
Small Scale ◽  
Spectral Structure ◽  
Electron Positron ◽  
Jitter Radiation ◽  
Transverse Deflection ◽  
Accelerated Particles

AbstractRecent PIC simulations of relativistic electron-positron (electron-ion) jets injected into a stationary medium show that particle acceleration occurs in the shocked regions. Simulations show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields and for particle acceleration. These magnetic fields contribute to the electron's transverse deflection behind the shock. The “jitter” radiation from deflected electrons in turbulent magnetic fields has properties different from synchrotron radiation calculated in a uniform magnetic field. This jitter radiation may be important for understanding the complex time evolution and/or spectral structure of gamma-ray bursts, relativistic jets in general, and supernova remnants. In order to calculate radiation from first principles and go beyond the standard synchrotron model, we have used PIC simulations. We present synthetic spectra to compare with the spectra obtained from Fermi observations.

scholarly journals Simulation of relativistic shocks and associated radiation from turbulent magnetic fields

2010 ◽  
Vol 6 (S275) ◽  
pp. 354-357 ◽  
Author(s):  
K.-I. Nishikawa ◽  
J. Niemiec ◽  
M. Medvedev ◽  
B. Zhang ◽  
P. Hardee ◽  
...  
Keyword(s):  
Particle Acceleration ◽  
Magnetic Fields ◽  
Supernova Remnants ◽  
Gamma Ray ◽  
Small Scale ◽  
Spectral Structure ◽  
Relativistic Shocks ◽  
Electron Positron ◽  
Jitter Radiation ◽  
Transverse Deflection

AbstractRecent PIC simulations of relativistic electron-positron (electron-ion) jets injected into a stationary medium show that particle acceleration occurs in the shocked regions. Simulations show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields and for particle acceleration. These magnetic fields contribute to the electron's transverse deflection behind the shock. The “jitter” radiation from deflected electrons in turbulent magnetic fields has different properties from synchrotron radiation calculated in a uniform magnetic field. This jitter radiation may be important for understanding the complex time evolution and/or spectral structure of gamma-ray bursts, relativistic jets in general, and supernova remnants. In order to calculate radiation from first principles and go beyond the standard synchrotron model, we have used PIC simulations. We will present detailed spectra for conditions relevant to various astrophysical sites of collisionless shock formation. In particular we will discuss application to GRBs and SNRs.

scholarly journals PARTICLE ACCELERATION, MAGNETIC FIELD GENERATION, AND ASSOCIATED EMISSION IN COLLISIONLESS RELATIVISTIC JETS

2008 ◽  
Vol 17 (10) ◽  
pp. 1761-1767 ◽  
Author(s):  
K.-I. NISHIKAWA ◽  
Y. MIZUNO ◽  
G. J. FISHMAN ◽  
P. HARDEE
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Small Scale ◽  
Spectral Structure ◽  
Relativistic Jets ◽  
Weibel Instability ◽  
Electron Positron ◽  
Jitter Radiation

Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., active galactic nuclei (AGNs), gamma-ray bursts (GRBs), and galactic microquasar systems usually have power-law emission spectra. Recent PIC simulations using injected relativistic electron-ion (electron-positron) jets show that acceleration occurs within the downstream jet. Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electrons' transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different properties to synchrotron radiation which assumes a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.

scholarly journals SIMULATION OF RELATIVISTIC JETS AND ASSOCIATED SELF-CONSISTENT RADIATION

2012 ◽  
Vol 08 ◽  
pp. 259-264 ◽  
Author(s):  
K.-I. NISHIKAWA ◽  
J. NIEMIEC ◽  
B. ZHANG ◽  
M. MEDVEDEV ◽  
P. HARDEE ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Supernova Remnants ◽  
Gamma Ray ◽  
Lorentz Factor ◽  
Shock Structure ◽  
Spectral Structure ◽  
Relativistic Jets ◽  
Collisionless Shocks ◽  
Electron Positron ◽  
Transverse Deflection

Plasma instabilities are responsible not only for the onset and mediation of collisionless shocks but also for the associated acceleration of particles. We have investigated particle acceleration and shock structure associated with an unmagnetized relativistic electron-positron jet propagating into an unmagnetized electron-positron plasma. Cold jet electrons are thermalized and slowed while the ambient electrons are swept up to create a partially developed hydrodynamic-like shock structure. In the leading shock, electron density increases by a factor of about 3.5 in the simulation frame. Strong electromagnetic fields are generated in the trailing shock and provide an emission site. These magnetic fields contribute to the electrons transverse deflection and, more generally, relativistic acceleration behind the shock. We have calculated, self-consistently, the radiation from electrons accelerated in the turbulent magnetic fields. We found that the synthetic spectra depend on the Lorentz factor of the jet, its thermal temperature and strength of the generated magnetic fields. The properties of the radiation may be important for understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets in general, and supernova remnants.

PARTICLE ACCELERATION AND MAGNETIC FIELD GENERATION IN SHEAR-FLOWS

2014 ◽  
Vol 28 ◽  
pp. 1460195
Author(s):  
K.-I. NISHIKAWA ◽  
P. HARDEE ◽  
Y. MIZUNO ◽  
I. DUŢAN ◽  
B. ZHANG ◽  
...  
Keyword(s):  
Particle Acceleration ◽  
Magnetic Fields ◽  
Lorentz Factor ◽  
Velocity Shear ◽  
Magnetic Field Generation ◽  
Electron Positron ◽  
Relativistic Jet ◽  
Unmagnetized Plasma ◽  
Alternating Magnetic Fields ◽  
Transverse Deflection

We have investigated the generation of magnetic fields associated with velocity shear between an unmagnetized relativistic (core) jet and an unmagnetized sheath plasma by the kinetic Kelvin-Helmholtz instability for different mass ratios (m i /m e = 1, 20, and 1836) and different jet Lorentz factors. We found that electron-positron cases have alternating magnetic fields instead of the DC magnetic fields found in electron-ion cases. We have also investigated particle acceleration and shock structure associated with an unmagnetized relativistic jet propagating into an unmagnetized plasma for electron-positron and electron-ion plasmas. Strong magnetic fields generated in the trailing shock lead to transverse deflection and acceleration of the electrons. We have self-consistently calculated the radiation from the electrons accelerated in the turbulent magnetic fields for different jet Lorentz factors. We find that the synthetic spectra depend on the bulk Lorentz factor of the jet, the jet temperature, and the strength of the magnetic fields generated in the shock.

scholarly journals Observational Constraints on the Maximum Energies of Accelerated Particles in Supernova Remnants: Low Maximum Energies and a Large Variety

2022 ◽  
Vol 924 (2) ◽  
pp. 45
Author(s):  
Hiromasa Suzuki ◽  
Aya Bamba ◽  
Ryo Yamazaki ◽  
Yutaka Ohira
Keyword(s):  
Particle Acceleration ◽  
Cosmic Rays ◽  
Supernova Remnants ◽  
Gamma Ray ◽  
Galactic Cosmic Rays ◽  
Maximum Energy ◽  
Average Maximum ◽  
Maximum Particle ◽  
Accelerated Particles ◽  
Age Estimates

Abstract Supernova remnants (SNRs) are thought to be the most promising sources of Galactic cosmic rays. One of the principal questions is whether they are accelerating particles up to the maximum energy of Galactic cosmic rays (∼PeV). In this work, a systematic study of gamma-ray-emitting SNRs is conducted as an advanced study of Suzuki et al. Our purpose is to newly measure the evolution of maximum particle energies with increased statistics and better age estimates. We model their gamma-ray spectra to constrain the particle-acceleration parameters. Two candidates of the maximum energy of freshly accelerated particles, the gamma-ray cutoff and break energies, are found to be well below PeV. We also test a spectral model that includes both the freshly accelerated and escaping particles to estimate the maximum energies more reliably, but no tighter constraints are obtained with current statistics. The average time dependences of the cutoff energy (∝t −0.81±0.24) and break energy (∝t −0.77±0.23) cannot be explained with the simplest acceleration condition (Bohm limit) and require shock–ISM (interstellar medium) interaction. The average maximum energy during lifetime is found to be ≲20 TeV ( t M / 1 kyr ) − 0.8 with t M being the age at the maximum, which reaches PeV if t M ≲ 10 yr. The maximum energies during lifetime are suggested to have a variety of 1.1–1.8 dex from object to object. Although we cannot isolate the cause of this variety, this work provides an important clue to understanding the microphysics of particle acceleration in SNRs.

scholarly journals High-energy emission from transients

2013 ◽  
Vol 371 (1992) ◽  
pp. 20120279 ◽  
Author(s):  
J. A. Hinton ◽  
R. L. C. Starling
Keyword(s):  
Particle Acceleration ◽  
Time Scales ◽  
Supernova Remnants ◽  
Gamma Ray ◽  
Experimental Situation ◽  
High Energy ◽  
Galactic Cosmic Rays ◽  
Time Variable ◽  
Wide Range ◽  
Cosmic Explosions

Cosmic explosions dissipate energy into their surroundings on a very wide range of time scales: producing shock waves and associated particle acceleration. The historical culprits for the acceleration of the bulk of Galactic cosmic rays are supernova remnants: explosions on approximately 10 4 year time scales. Increasingly, however, time-variable emission points to rapid and efficient particle acceleration in a range of different astrophysical systems. Gamma-ray bursts have the shortest time scales, with inferred bulk Lorentz factors of approximately 1000 and photons emitted beyond 100 GeV, but active galaxies, pulsar wind nebulae and colliding stellar winds are all now associated with time-variable emission at approximately teraelectron volt energies. Cosmic photons and neutrinos at these energies offer a powerful probe of the underlying physical mechanisms of cosmic explosions, and a tool for exploring fundamental physics with these systems. Here, we discuss the motivations for high-energy observations of transients, the current experimental situation, and the prospects for the next decade, with particular reference to the major next-generation high-energy observatory, the Cherenkov Telescope Array.

scholarly journals GRB spectral parameter modeling

2010 ◽  
Vol 6 (S274) ◽  
pp. 243-245
Author(s):  
Gregory D. Fleishman ◽  
Fedor A. Urtiev
Keyword(s):  
Synchrotron Radiation ◽  
Electric Fields ◽  
Large Scale ◽  
Gamma Ray ◽  
Small Scale ◽  
Random Waves ◽  
Spectral Parameters ◽  
Random Magnetic Field ◽  
Cross Correlations ◽  
Accelerated Particles

AbstractFireball model of the gamma-ray bursts (GRBs) predicts generation of numerous internal shocks, which efficiently accelerate charged particles and generate relatively small-scale stochastic magnetic and electric fields. The accelerated particles diffuse in space due to interaction with the random waves and so emit so called Diffusive Synchrotron Radiation (DSR) in contrast to standard synchrotron radiation they would produce in a large-scale regular magnetic fields. In this contribution we present key results of detailed modeling of the GRB spectral parameters, which demonstrate that the non-perturbative DSR emission mechanism in a strong random magnetic field is consistent with observed distributions of the Band parameters and also with cross-correlations between them.

scholarly journals RELATIVISTIC SHOCK ACCELERATION AND SOME CONSEQUENCES

2014 ◽  
Vol 28 ◽  
pp. 1460166 ◽  
Author(s):  
MARTIN LEMOINE ◽  
GUY PELLETIER
Keyword(s):  
Particle Acceleration ◽  
Gamma Ray ◽  
Light Curves ◽  
Shock Acceleration ◽  
Theoretical Understanding ◽  
Relativistic Shock ◽  
Multi Wavelength ◽  
The Impact ◽  
Wavelength Light ◽  
Accelerated Particles

This paper summarizes recent progresses in our theoretical understanding of particle acceleration at relativistic shock waves and it discusses two salient consequences: (1) the maximal energy of accelerated particles; (2) the impact of the shock-generated micro-turbulence on the multi-wavelength light curves of gamma-ray burst afterglows.

scholarly journals Cosmic-ray driven dynamo in galactic disks

2008 ◽  
Vol 4 (S259) ◽  
pp. 479-484 ◽  
Author(s):  
Michał Hanasz ◽  
K. Otmianowska-Mazur ◽  
H. Lesch ◽  
G. Kowal ◽  
M. Soida ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Supernova Remnants ◽  
Large Scale ◽  
Cosmic Ray ◽  
Turbulent Energy ◽  
Field Energy ◽  
Small Scale ◽  
Galactic Rotation ◽  
Dynamo Action ◽  
Magnetic Field Energy

AbstractWe present new developments on the Cosmic–Ray driven, galactic dynamo, modeled by means of direct, resistive CR–MHD simulations, performed with ZEUS and PIERNIK codes. The dynamo action, leading to the amplification of large–scale galactic magnetic fields on galactic rotation timescales, appears as a result of galactic differential rotation, buoyancy of the cosmic ray component and resistive dissipation of small–scale turbulent magnetic fields. Our new results include demonstration of the global–galactic dynamo action driven by Cosmic Rays supplied in supernova remnants. An essential outcome of the new series of global galactic dynamo models is the equipartition of the gas turbulent energy with magnetic field energy and cosmic ray energy, in saturated states of the dynamo on large galactic scales.

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