Kelvin-Helmholtz driven propeller in AE Aquarii: A unified model for thermal and non-thermal flares

Venter, L.; Meintjes, Pieter

doi:10.1111/j.1365-2966.2005.09877.x

Cited by 12 publications

(20 citation statements)

References 40 publications

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“…The emission in this wavelength band is attributed to synchrotron radiation of expanding magnetized blobs of electrons (e.g. Bastian et al 1988; Meintjes & Venter 2003; Venter & Meintjes 2006) which become optically thin (and hence the electrons follow a power‐law distribution), and subsequently emit the observed non‐thermal radiation. The near‐IR, optical and near‐UV data are fitted with a thermal blackbody model (bb) of temperature of T bb ≃ 4.65 × 10 3 K, associated with the secondary star companion.…”

Section: Spectral Energy Distribution Of Ae Aqrmentioning

confidence: 99%

X-ray characteristics and the spectral energy distribution of AE Aquarii

Oruru

Meintjes

2012

Monthly Notices of the Royal Astronomical Society

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Using data from contemporaneous observations with Chandra and Swift, it is shown that the X‐ray emission below 10 keV is predominantly thermal, characterized by flares and emission lines and dominated by the soft component. The Chandra and Swift X‐ray spectra (EX≤ 10 keV) can be reproduced by multicomponent thermal emission models with a time‐averaged X‐ray luminosity of LX∼ 1031 erg s−1. The pulsed 33‐s soft X‐ray emission below 10 keV is confirmed in both the Chandra and Swift data sets. The epoch of pulse maximum of the 33‐s white dwarf spin period is consistent with the recently derived ephemeris based upon Suzaku measurements. The recently detected Suzaku hard X‐ray component above 10 keV shows a non‐thermal power‐law nature, with a photon index of Γ∼ 1.2, possibly the result of synchrotron emission of high‐energy electrons in the white dwarf magnetosphere. The hard X‐ray luminosity of LX,hard≤ 5 × 1030 erg s−1 also constitutes κ∼ 0.1 per cent of the total spin‐down luminosity of the white dwarf. This places AE Aquarii in the same category as young spin‐powered pulsars between 2 and 20 keV. Additionally, it is shown that electrons can be accelerated to energies in excess of 10 TeV outside the light cylinder radius, providing interesting possibilities for VHE‐TeV follow‐up observations. The X‐ray emission below EX≤ 10 keV, on the other hand, is explained in terms of plasma heating at the magnetospheric radius, the result of the dissipation of gravitational potential energy. It is found that a conversion efficiency of α∼ 0.01 is sufficient to heat the plasma at the magnetospheric boundary to temperatures kT≤ 10 keV, sufficient to drive the X‐ray emission below 10 keV. Only a small fraction (β∼ 0.3 per cent) of the mass flow at the magnetospheric radius eventually accretes on to the surface of the white dwarf, emphasizing the very effective magnetospheric propeller process in the system.

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Section: Spectral Energy Distribution Of Ae Aqrmentioning

confidence: 99%

X-ray characteristics and the spectral energy distribution of AE Aquarii

Oruru

Meintjes

2012

Monthly Notices of the Royal Astronomical Society

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“…The KH instability has been studied in a variety of astrophysical systems, from solar winds (Hasegawa et al 2004; Bettarini et al 2006; Amerstorfer et al 2007) and pulsar winds (Bucciantini & Del Zanna 2006) to thermal flares (Venter & Meintjes 2006). Due to its ability to drive mixing and turbulence, the KH instability has been considered relevant in protoplanetary discs (Gómez & Ostriker 2005; Johansen, Henning & Klahr 2006), accretion discs and magnetospheres (Li & Narayan 2004) and other jets and outflows (Baty & Keppens 2006).…”

Section: Introductionmentioning

confidence: 99%

The Kelvin-Helmholtz instability in weakly ionized plasmas: ambipolar-dominated and Hall-dominated flows

Jones¹,

Downes²

2011

Monthly Notices of the Royal Astronomical Society

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The Kelvin-Helmholtz instability is well known to be capable of converting well-ordered flows into more disordered, even turbulent, flows. As such it could represent a path by which the energy in, for example, bow shocks from stellar jets could be converted into turbulent energy thereby driving molecular cloud turbulence. We present the results of a suite of fully multifluid magnetohydrodynamic simulations of this instability using the HYDRA code. We investigate the behaviour of the instability in a Hall-dominated and an ambipolar diffusion dominated plasma as might be expected in certain regions of accretion discs and molecular clouds, respectively.We find that, while the linear growth rates of the instability are unaffected by multifluid effects, the non-linear behaviour is remarkably different with ambipolar diffusion removing large quantities of magnetic energy while the Hall effect, if strong enough, introduces a dynamo effect which leads to continuing strong growth of the magnetic field well into the non-linear regime and a lack of true saturation of the instability.

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“…The main distinguishing feature of this cataclysmic variable is that the mass transfer from the red dwarf secondary star to the white dwarf primary is mostly not accreted, but ejected by the fast rotating primary's magnetic field, which acts as a propeller (e.g. Wynn et al 1997; Meintjes & Venter 2005; Venter & Meintjes 2006). This results in the white dwarf exhibiting a spin‐down resulting in a spin‐down luminosity of P sd ∼ 10 34 erg s −1 (de Jager et al 1994; Meintjes & de Jager 2000), providing the reservoir for the majority of the emission from radio to TeV γ‐rays.…”

Section: Introductionmentioning

confidence: 99%

A tenuous X-ray corona enveloping AE Aquarii

Venter

Meintjes

2007

Monthly Notices of the Royal Astronomical Society

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In this paper we propose that the observed unpulsed X-ray emission in AE Aquarii is the result of a very tenuous hot corona associated with the secondary star, which is pumped magnetohydrodynamically by the propeller action of the fast rotating white dwarf. It is shown that the closed coronal field of the secondary star envelops a substantial portion of the binary system, including the fast rotating magnetized white dwarf. This implies that the propeller outflow of material in AE Aquarii is initiated inside an enveloping magnetic cavity. The outflow crossing the secondary dead-zone field constitutes a β gen = (8πρv 2 esc /B 2 ) 1 plasma, acting as a magnetohydrodynamic generator resulting in the induction of field-aligned currents in these closed magnetospheric circuits where β cir = (8πnkT/B 2 ) 1. The Ohmic heating of the coronal circuit can readily account for a T x 10 7 K plasma in the coronal flux tubes connecting the generator and the stellar surface. Further, the bremsstrahlung losses of the thermal electrons in the coronal circuit can readily drive the observed unpulsed X-ray luminosity of L x ∼ 10 31 erg s −1 , which correlates with the luminosity and relatively large source implied by recent XMM-Newton observations.

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Kelvin-Helmholtz driven propeller in AE Aquarii: A unified model for thermal and non-thermal flares

Cited by 12 publications

References 40 publications

X-ray characteristics and the spectral energy distribution of AE Aquarii

X-ray characteristics and the spectral energy distribution of AE Aquarii

The Kelvin-Helmholtz instability in weakly ionized plasmas: ambipolar-dominated and Hall-dominated flows

A tenuous X-ray corona enveloping AE Aquarii

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