Electron-Ion Temperature Equilibration in Collisionless Shocks: The Supernova Remnant-Solar Wind Connection

Ghavamian, Parviz; Schwartz, S. J.; Mitchell, J. J.; Masters, A.; Laming, J. M.

doi:10.1007/s11214-013-9999-0

Cited by 108 publications

(122 citation statements)

References 109 publications

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“…Electron-ion temperature difference: if the shock wave heats ions, but not electrons, as is observed to occur in collisionless shocks in supernova remnants (Ghavamian et al 2013), the electrons are gradually heated by Coulomb collisions. The result is that the peak electron temperature is a bit lower than the nominal shock temperature, and the electrons stay near that peak temperature longer than in a single temperature flow.…”

Section: Discussionmentioning

confidence: 97%

Testing the cooling flow model in the intermediate polar EX Hydrae

Luna

Raymond

Brickhouse

et al. 2015

A&A

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We use the best available X-ray data from the intermediate polar EX Hydrae to study the cooling-flow model often applied to interpret the X-ray spectra of these accreting magnetic white dwarf binaries. First, we resolve a long-standing discrepancy between the X-ray and optical determinations of the mass of the white dwarf in EX Hya by applying new models of the inner disk truncation radius. Our fits to the X-ray spectrum now agree with the white dwarf mass of 0.79 M determined using dynamical methods through spectroscopic observations of the secondary. We use a simple isobaric cooling flow model to derive the emission line fluxes, emission measure distribution, and H-like to He-like line ratios for comparison with the 496 ks Chandra High Energy Transmission Grating observation of EX Hydrae. We find that the H/He ratios are not well reproduced by this simple isobaric cooling flow model and show that while H-like line fluxes can be accurately predicted, fluxes of lower-Z He-like lines are significantly underestimated. This discrepancy suggests that an extra heating mechanism plays an important role at the base of the accretion column, where cooler ions form. We thus explored more complex cooling models, including the change of gravitational potential with height in the accretion column and a magnetic dipole geometry. None of these modifications to the standard cooling flow model are able to reproduce the observed line ratios. While a cooling flow model with subsolar (0.1 ) abundances is able to reproduce the line ratios by reducing the cooling rate at temperatures lower than ∼10 7.3 K, the predicted line-to-continuum ratios are much lower than observed. We discuss and discard mechanisms, such as photoionization, departures from constant pressure, resonant scattering, different electronion temperatures, and Compton cooling. Thermal conduction transfers energy from the region above 10 7 K, where the H-like lines are mostly formed, to the cooler regions where the He-like ions of the lower-Z elements are formed, hence in principle it could help resolve the problem. However, simple models indicate that the energy is deposited below 10 6 K, which is too cool to increase the emission of the He-like lines we observe. We conclude that some other effect, such as thermally unstable cooling, modifies the temperature distribution.

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Section: Discussionmentioning

confidence: 97%

Testing the cooling flow model in the intermediate polar EX Hydrae

Luna

Raymond

Brickhouse

et al. 2015

A&A

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“…Such a regime may be relevant for the solar corona (e.g., Chandran et al 2011), hot accretion flows (e.g., Quataert 1998), collisionless shocks (e.g., Treumann 2009;Ghavamian et al 2013;Chen & Boldyrev 2017), etc. The tearing mode calculation proceeds in the usual way; it is not hard to see that the most unstable tearing mode is such that Δ′δ∼1 and δ∼d e .…”

Section: Reconnection In the Kinetic Turbulence Rangementioning

confidence: 99%

Collisionless Reconnection in Magnetohydrodynamic and Kinetic Turbulence

Loureiro

Boldyrev

2017

ApJ

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It has recently been proposed that the inertial interval in magnetohydrodynamic (MHD) turbulence is terminated at small scales not by a Kolmogorov-like dissipation region, but rather by a new sub-inertial interval mediated by tearing instability. However, many astrophysical plasmas are nearly collisionless so the MHD approximation is not applicable to turbulence at small scales. In this paper, we propose an extension of the theory of reconnectionmediated turbulence to plasmas which are so weakly collisional that the reconnection occurring in the turbulent eddies is caused by electron inertia rather than by resistivity. We find that the transition scale to reconnectionmediated turbulence depends on the plasma beta and on the assumptions of the plasma turbulence model. However, in all of the cases analyzed, the energy spectra in the reconnection-mediated interval range from μ^-(

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“…Observationally, one finds with few exceptions a correlation of µ -T T v e i sh 2 (for a review see Ghavamian et al 2013). A conceptual explanation for this empirical relation lies in electron heating through turbulence generated by reflected ions whose number depends on the shock speed.…”

Section: Structure Of the Forward Shockmentioning

confidence: 99%

Nonrelativistic Perpendicular Shocks Modeling Young Supernova Remnants: Nonstationary Dynamics and Particle Acceleration at Forward and Reverse Shocks

Wieland

Pohl

Niemiec

et al. 2016

ApJ

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For parameters that are applicable to the conditions at young supernova remnants, we present results of twodimensional, three-vector (2D3V)particle-in-cell simulations of a non-relativistic plasma shock with a large-scale perpendicular magnetic field inclined at a  45 angle to the simulation plane to approximate three-dimensional (3D) physics. We developed an improved clean setup that uses the collision of two plasma slabs with different densities and velocities, leading to the development of two distinctive shocks and a contact discontinuity. The shock formation is mediated by Weibel-type filamentation instabilities that generate magnetic turbulence. Cyclic reformation is observed in both shocks with similar period, for which we note global variations due to shock rippling and local variations arising from turbulent current filaments. The shock rippling occurs on spatial and temporal scales produced by the gyro-motions of shock-reflected ions. The drift motion of electrons and ions is not a gradient drift, but is commensurate withÉ B drift. We observe a stable supra-thermal tail in the ion spectra, but no electron acceleration because the amplitude of the Buneman modes in the shock foot is insufficient for trapping relativistic electrons. We see no evidence of turbulent reconnection. A comparison with other twodimensional (2D) simulation results suggests that the plasma beta and the ion-to-electron mass ratio are not decisive for efficient electron acceleration, but the pre-acceleration efficacy might be reduced with respect to the 2D results once 3D effects are fully accounted for. Other microphysical factors may also play a part in limiting the amplitude of the Buneman waves or preventing the return of electrons to the foot region.

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Electron-Ion Temperature Equilibration in Collisionless Shocks: The Supernova Remnant-Solar Wind Connection

Cited by 108 publications

References 109 publications

Testing the cooling flow model in the intermediate polar EX Hydrae

Testing the cooling flow model in the intermediate polar EX Hydrae

Collisionless Reconnection in Magnetohydrodynamic and Kinetic Turbulence

Nonrelativistic Perpendicular Shocks Modeling Young Supernova Remnants: Nonstationary Dynamics and Particle Acceleration at Forward and Reverse Shocks

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