Particle Acceleration in Relativistic Collisionless Shocks: Fermi Process at Last?

Spitkovsky, Anatoly

doi:10.1086/590248

Cited by 557 publications

(585 citation statements)

References 25 publications

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“…We also note that the model presented by Spitkovsky (2008), in which the shock acceleration process is studied in a selfconsistent fashion, provides results that are consistent with our phenomenological picture. The result from this numerical study is a relativistic Maxwellian, and a high-energy tail with s = 2.4 ± 0.1, plus an exponential cut-off moving to higher energies with time of the simulation.…”

Section: Discussionsupporting

confidence: 87%

“…A more careful analysis indicates that such a contradiction is only apparent. As demonstrated by Spitkovsky (2008), diffusive shock acceleration models rely on the presence of a magnetic turbulence close to the shock responsible for the scattering process, although these models do not clearly determine the possible role of turbulence in the acceleration. Our observational analysis appears to indicate the simultaneous roles of the first and second order processes, where the stochastic acceleration arises from the magnetic turbulence and is indicated by the curvature and more generally by the E p − b relation, and the first order is indicated by the slope of the electron power-law tail.…”

Section: Discussionmentioning

confidence: 99%

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Swift observations of the very intense flaring activity of Mrk 421 during 2006. I. Phenomenological picture of electron acceleration and predictions for MeV/GeV emission

Tramacere¹,

Giommi

Perri

et al. 2009

A&A

276

295

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Aims. We present the results of a deep spectral analysis of all Swift observations of Mrk 421 between April 2006 and July 2006, when it reached its highest X-ray flux recorded until the end of 2006. The peak flux was about 85 milli-Crab in the 2.0-10.0 keV band, and the peak energy (E p ) of the spectral energy distribution (SED) was often at energies higher than 10 keV. We study trends between the spectral parameters, and the physical insights the parameters provide into the underlying acceleration and emission mechanisms. Methods. We performed a spectral analysis of Swift observations to investigate trends between the spectral parameters. We searched for acceleration and energetic features phenomenologically linked to the SSC model parameters, by predicting their effects in the γ-ray band, and in particular, the spectral shape expected in the Fermi Gamma-ray Space Telescope-LAT band. Results. We confirm that the X-ray spectrum is described well by a log-parabolic distribution close to E p , that the peak flux of the SED (S p ) is correlated with E p , and that E p is anti-correlated with the curvature parameter (b). The spectral evolution in the Hardness-ratio-flux plane shows both clockwise and counter-clockwise patterns. During the most energetic flares, the UV-to-soft-X-ray spectral shape requires an electron distribution spectral index of s 2.3. Conclusions. We demonstrate that the UV-to-X-ray emission from Mrk 421 is probably generated by a population of electrons that is actually curved, and has a low energy power-law tail. The observed spectral curvature is consistent with both stochastic acceleration or energy-dependent acceleration probability mechanisms, whereas the power-law slope of XRT-UVOT data is close to that inferred from the GRBs X-ray afterglow and in agreement with the universal first-order relativistic shock acceleration models. This scenario implies that magnetic turbulence may play a twofold role: spatial diffusion relevant to the first order process and momentum diffusion relevant to the second order process.

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Section: Discussionsupporting

confidence: 87%

Section: Discussionmentioning

confidence: 99%

Swift observations of the very intense flaring activity of Mrk 421 during 2006. I. Phenomenological picture of electron acceleration and predictions for MeV/GeV emission

Tramacere¹,

Giommi

Perri

et al. 2009

A&A

276

295

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“…This agrees with recent numerical simulations of relativistic collisionless shocks (Spitkovsky 2008), if a significant fraction of the hadrons interacts and generates π 0 .…”

Section: Energetic Considerationssupporting

confidence: 92%

ηCarinae: a very large hadron collider

Farnier

Walter

Leyder

2010

A&A

109

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Context. η Carinae is the colliding wind binary with the highest mass-loss rate in our Galaxy and the only one in which hard X-ray emission has been detected. Aims. η Carinae is therefore a primary candidate to search for particle acceleration by probing its gamma-ray emission. Methods. We used the first 21 months of Fermi/LAT data to extract gamma-ray (0.2-100 GeV) images, spectra, and light-curves, then combined them with multi-wavelength observations to model the non-thermal spectral energy distribution. Results. A bright gamma-ray source is detected at the position of η Carinae. Its flux at a few 100 MeV can be modelled by an extrapolation of the hard X-ray spectrum towards higher energies. The spectral energy distribution features two distinct components. The first one extends from the keV to GeV energy range, and features an exponential cutoff at ∼1 GeV. It can be understood as inverse Compton scattering of ultraviolet photons by electrons accelerated up to γ ∼ 10 4 in the colliding wind region. The expected synchrotron emission is compatible with the existing upper limit to the non-thermal radio emission. The second component is a hard gamma-ray tail detected above 20 GeV. It could be explained by π 0 -decay of accelerated hadrons interacting with the dense stellar wind. The ratio of the fluxes of the π 0 to inverse Compton components is roughly as predicted by simulations of colliding wind binaries. This hard gamma-ray tail can only be understood if emitted close to the wind collision region. The energy transferred to the accelerated particles (∼5% of the collision mechanical energy) is comparable to that of the thermal X-ray emission. Conclusions. The electron spectrum responsible for the keV to GeV emission was modelled and the observed emission above 20 GeV strongly suggests hadronic acceleration in η Carinae. These observations are thus in good agreement with the colliding wind scenario proposed for η Carinae.

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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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Particle Acceleration in Relativistic Collisionless Shocks: Fermi Process at Last?

Cited by 557 publications

References 25 publications

Swift observations of the very intense flaring activity of Mrk 421 during 2006. I. Phenomenological picture of electron acceleration and predictions for MeV/GeV emission

Swift observations of the very intense flaring activity of Mrk 421 during 2006. I. Phenomenological picture of electron acceleration and predictions for MeV/GeV emission

ηCarinae: a very large hadron collider

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

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