Diffusive Acceleration of Particles at Oblique, Relativistic, Magnetohydrodynamic Shocks

Summerlin, Errol J.; Baring, Matthew G.

doi:10.1088/0004-637x/745/1/63

Cited by 163 publications

(253 citation statements)

References 85 publications

(230 reference statements)

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“…This is in agreement with numerical simulations of relativistic shocks, which have demonstrated that diffusive shock acceleration forms such power-law spectra (Achterberg et al 2001;Spitkovsky 2008;Summerlin & Baring 2012). Therefore, shocks are frequently used to explain blazar flaring activities.…”

Section: Introductionsupporting

confidence: 89%

Polarization Signatures of Relativistic Magnetohydrodynamic Shocks in the Blazar Emission Region. I. Force-Free Helical Magnetic Fields

Zhang

Deng

et al. 2016

ApJ

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The optical radiation and polarization signatures in blazars are known to be highly variable during flaring activities. It is frequently argued that shocks are the main driver of the flaring events. However, the spectral variability modelings generally lack detailed considerations of the self-consistent magnetic field evolution modeling; thus, so far the associated optical polarization signatures are poorly understood. We present the first simultaneous modeling of the optical radiation and polarization signatures based on 3D magnetohydrodynamic simulations of relativistic shocks in the blazar emission environment, with the simplest physical assumptions. By comparing the results with observations, we find that shocks in a weakly magnetized environment will largely lead to significant changes in the optical polarization signatures, which are seldom seen in observations. Hence an emission region with relatively strong magnetization is preferred. In such an environment, slow shocks may produce minor flares with either erratic polarization fluctuations or considerable polarization variations, depending on the parameters; fast shocks can produce major flares with smooth polarization angle rotations. In addition, the magnetic fields in both cases are observed to actively revert to the original topology after the shocks. All these features are consistent with observations. Future observations of the radiation and polarization signatures will further constrain the flaring mechanism and the blazar emission environment.

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Section: Introductionsupporting

confidence: 89%

Polarization Signatures of Relativistic Magnetohydrodynamic Shocks in the Blazar Emission Region. I. Force-Free Helical Magnetic Fields

Zhang

Deng

et al. 2016

ApJ

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“…The same observations are evident as well in the works of e.g. Ellison & Double (2004), Baring (2004), Niemiec & Ostrowski (2004), and Summerlin & Baring (2012). In other words, Monte Carlo simulation studies independently showed that there is an absent "universal" powerlaw spectrum in relativistic shocks, and a variety of spectral indices depending either on shock inclinations, shock speeds, or scattering operators.…”

Section: Single-oblique Relativistic Shock Studiessupporting

confidence: 68%

“…Because we aim to consolidate the understanding of the results that will follow, we recapitulate and discuss here a selection of previous numerical studies based on the MQ03 Monte Carlo code for single relativistic shocks, and compare them with similar studies of Ellison & Double (2004), Niemiec & Ostrowski (2004), Baring (2004), and Summerlin & Baring (2012). As we will see in Sect.…”

Section: Single-oblique Relativistic Shock Studiesmentioning

confidence: 98%

Active galactic nuclei jets and multiple oblique shock acceleration: starved spectra

Meli¹,

Biermann

2013

A&A

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Context. Shocks in jets and hot spots of active galactic nuclei (AGN) are one prominent class of possible sources of very high-energy cosmic-ray particles (above 10 18 eV). Extrapolating their spectrum to their plausible injection energy from some shock implies an enormous hidden energy for a spectrum of index ∼−2. Some analyses suggest the particles' injection spectrum at source to be as steep as −2.4 to −2.7, which exacerbates the problem, by a factor of 10 6 . Nevertheless, it seems implausible that more than at the very best 1/3 of the jet energy goes into the required flux of energetic particles, thus one would need to allow for the possibility that there is an energy problem, which we would like to address in this work. Aims. Sequences of consecutive oblique shock features, or conical shocks, have been theoretically predicted and eventually observed in many AGN jets. Based on that, we use by analogy the Comptonization effect and propose a scenario of a single injection of particles consecutively accelerated by several oblique shocks along the axis of an AGN jet. Methods. We developed a test-particle approximation Monte Carlo simulations to calculate particle spectra by acceleration at such a shock pattern while monitoring the efficiency of acceleration by calculating differential spectra. Results. We find that the first shock of a sequence of oblique shocks establishes a low-energy power-law spectrum with ∼E −2.7 . The following consecutive shocks push the spectrum up in energy, rendering flatter distributions with steep cut-offs, and characteristic depletion at low energies, which could explain the puzzling apparent extra source power. Conclusions. Our numerical calculations show a variation of spectral indices, a general spectral flattening, and starved spectra, which connect to the relativistic nature of the shocks, the multiple shock acceleration conditions, and the steepness of the magnetic field to the shock normal. This helps in understanding the jet-magnetic field geometry and the irregular or flat spectra observed in many AGN jets (e.g., CenA, 3C 279, PKS 1510-089). Furthermore, the E −2.4 − E −2.7 ultra-high-energy cosmic-ray injected source spectra claimed by many authors might be explained by the superposition of several, perhaps many, emission sources, all of which end their particle shock-acceleration sequence with flatter, starved spectra produced by two or more consecutive oblique shocks along their jets. It might also imply a mixed component of the accelerated particles above 10 19 eV. Moreover, the present acceleration model can explain the variability of inverted gamma-ray spectra observed in high redshifted flaring extragalactic sources.

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“…Further energization can occur in those cells where the magnetic field is oriented favorably. The TEMZ code very roughly includes this effect by allowing the maximum energy in rest-mass units, γ max , of the electrons to increase by a specified factor (left as a free parameter, with a value of 20 in the current BL Lac simulation) if the magnetic field is oriented nearly parallel to the shock normal-the "subluminal" regime within which some particles can cross the shock multiple times before they are swept downstream with the flow (see, e.g., Summerlin & Baring 2012). This creates an extension to the electron energy distribution at the high-energy end in some of the cells.…”

mentioning

confidence: 99%

Erratic Flaring of Bl Lac in 2012–2013: Multiwavelength Observations

Wehrle

Grupe

Jorstad

et al. 2016

ApJ

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BL Lac, the eponymous blazar, flared to historically high levels at millimeter, infrared, X-ray, and gamma-ray wavelengths in 2012. We present observations made with Herschel, Swift, NuSTAR, Fermi, the Submillimeter Array, CARMA, and the VLBA in 2012-2013, including three months with nearly daily sampling at several wavebands. We have also conducted an intensive campaign of 30 hr with every-orbit observations by Swift and NuSTAR, accompanied by Herschel, and Fermi observations. The source was highly variable at all bands. Time lags, correlations between bands, and the changing shapes of the spectral energy distributions can be explained by synchrotron radiation and inverse Compton emission from nonthermal seed photons originating from within the jet. The passage of four new superluminal very long baseline interferometry knots through the core and two stationary knots about 4 pc downstream accompanied the high flaring in 2012-2013. The seed photons for inverse Compton scattering may arise from the stationary knots and from a Mach disk near the core where relatively slowmoving plasma generates intense nonthermal radiation. The 95 spectral energy distributions obtained on consecutive days form the most densely sampled, broad wavelength coverage for any blazar. The observed spectral energy distributions and multi-waveband light curves are similar to simulated spectral energy distributions and light curves generated with a model in which turbulent plasma crosses a conical shock with a Mach disk.

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Diffusive Acceleration of Particles at Oblique, Relativistic, Magnetohydrodynamic Shocks

Cited by 163 publications

References 85 publications

Polarization Signatures of Relativistic Magnetohydrodynamic Shocks in the Blazar Emission Region. I. Force-Free Helical Magnetic Fields

Polarization Signatures of Relativistic Magnetohydrodynamic Shocks in the Blazar Emission Region. I. Force-Free Helical Magnetic Fields

Active galactic nuclei jets and multiple oblique shock acceleration: starved spectra

Erratic Flaring of Bl Lac in 2012–2013: Multiwavelength Observations

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