Extension of the radio spectrum of AE Aqr to the sub-millimetric range

Abada-Simon, M.; Bastian, T. S.; Bookbinder, Jay A.; Aubier, M. G.; Bromage, G. E.; Dulk, G. A.; Lecacheux, A.

doi:10.1007/3-540-60057-4_290

Cited by 8 publications

(7 citation statements)

References 8 publications

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“…It has been shown that with fairly modest parameter choices the trend of the observed spectrum (cf. Abada‐Simon et al 1993; Dubus et al 2004; Abada‐Simon et al 1995a,b) can be reproduced from radio (Abada‐Simon et al 1993, 1995a,b; Bastian et al 1998) to mid‐IR (Dubus et al 2004). The blob origin model for the radio‐IR emission in the system is thus compatible with the propeller mechanism proposed above.…”

Section: Radio Flaresmentioning

confidence: 99%

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

Venter

Meintjes

2006

Monthly Notices of the Royal Astronomical Society

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In this paper, an attempt is made to integrate the propeller ejection of material by the fast rotating white dwarf in AE Aquarii with the highly transient thermal and non‐thermal emission in a single unifying model. It has been shown that the violent interaction between the fast rotating magnetosphere and a clumpy fragmented stream, in AE Aquarii specifically, may result in the growth of unstable modes of the Kelvin–Helmholtz instability and associated turbulence over length scales comparable to the stream radius on time‐scales τK‐H ∼ tdyn (∼ 600 s). For all conversion efficiencies of magnetohydrodynamic (MHD) power to mechanical energy ε≥ 0.1, these instabilities result in the effective azimuthal acceleration of the gas parcels to the escape velocity over time‐scales tacc≤ 1000 s (∼tdyn). Further, it has been shown that the turbulence in the flow will cascade down to the dissipative level over time‐scales τcas∼ 3 h. If released through dissipative shocks, this reservoir can drive a luminosity of L∼ 1033 erg s−1, which can significantly contribute to the total emission when blobs collide in the exit stream, resulting in shock heating and associated flares. During the propeller process, particles can also be accelerated to high energies, which may be the driving mechanism behind the non‐thermal radio to mid‐infrared emission. The confluence of these ejected magnetized clouds may result in radio remnant surrounding AE Aquarii, which is optically thin between frequencies ν≥ 100 MHz–1 GHz.

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Section: Radio Flaresmentioning

confidence: 99%

“…Also included in Fig. 4 are a selection of observations (Abada‐Simon et al 1993, 1995a; Dubus et al 2004; Abada‐Simon Bastian & Bookbinder 1995b) that show the average trend of the spectrum with a gradient of approximately α≈ 0.5 (e.g. Dubus et al 2004).…”

Section: Radio Flaresmentioning

confidence: 99%

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

Venter

Meintjes

2006

Monthly Notices of the Royal Astronomical Society

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“…AE Aquarii displays peculiar non-thermal radio to infrared (IR) variability (Bastian et al 1988;Abada-Simon et al 1993, 1995aAbada-Simon, Bastian & Bookbinder 1995b;Abada-Simon et al 1998), and possibly also transient VHE γ -ray emission (e.g. Meintjes et al 1992Meintjes et al , 1994Meintjes & de Jager 2000).…”

Section: R a D I O F L A R E Smentioning

confidence: 99%

The diamagnetic blob propeller in AE Aquarii and non-thermal radio to mid-infrared emission

Meintjes

Venter

2005

Monthly Notices of the Royal Astronomical Society

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This paper presents a qualitative investigation of the propeller mechanism in AE Aquarii within the framework of the magnetohydrodynamic (MHD) interaction between the fast rotating magnetosphere of the white dwarf and a blobby mass flow stream from the secondary star. It has been shown that the denser part of the mass flow can penetrate the fast rotating magnetosphere of the white dwarf to the circularization radius, before it is ejected from the system. It has been shown that the total MHD power dissipated on a volume of material equivalent to an orbiting ring of cross‐sectional radius Rstream∼ 109 cm, at the circularization radius, is PMHD∼ 1034 erg s−1, which is of the same order of magnitude as the inferred spin‐down power of the white dwarf. Mixing of the magnetospheric field with a turbulent gas stream due to turbulent diffusion and Kelvin–Helmholtz instabilities, creating magnetic vortices in the flow, results in a transfer of mechanical energy to the stream, accelerating it like a slingshot to velocities exceeding the escape velocity over time‐scales far too short for viscous spreading of the material into a disc. The diffusion of the field into the turbulent gas probably results in stripping of the magnetospheric field through fast reconnection as a result of the huge differential rotation, resulting in the creation of magnetized plasma clouds with fields of Bcloud≥ 300 G. It has been shown that the interaction of the white dwarf field with the magnetized blob can accelerate electrons to energies of at least εe∼ 130 MeV within the dominant energy‐loss time‐scales, which is high enough to account for the maximum electron energies of εmax∼ 80 MeV, inferred from the latest detection of possible non‐thermal emission at frequencies ν∼ 17 000 GHz and 25 000 GHz, using the Keck I Telescope in Hawaii. It has been shown that the efficiency of the MHD propeller in converting thermal electrons to relativistic electrons, energetic enough to drive the total observed non‐thermal emission in AE Aquarii, is probably of the order of ∼0.1 per cent. This is consistent with the ratio (β∼ 0.1 per cent) of the total observed radio to mid‐infrared synchrotron emission to the total spin‐down power of the white dwarf. Based upon energy arguments, it has been shown that magnetized synchrotron‐emitting clouds with fields of Beq∼ 300 G, which is similar to the magnetospheric field at the main interaction zone, i.e. the circularization radius, can confine a population of relativistic electrons that are able to power the total observed non‐thermal radio to mid‐infrared emission with luminosity LR–IR∼ 1031 erg s−1.

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“…All this points to there being no dust in the environment of AE Aqr as in the majority of other CV systems. Figure 3 shows that both the ISOPHOT-C 90 µm and IRAS 60 µm detections, the ISOPHOT-C 170 µm upper limit, and the older JCMT 761 µm average flux (Abada-Simon et al 1995b) are of the same order of magnitude. The two ISOPHOT-C measurements are in agreement with, but more constraining than the IRAS upper limit at 100 µm.…”

Section: First Implications From the Infrared Measurementsmentioning

confidence: 90%

“…Flares were subsequently observed in the millimetre (Abada-Simon et al 1993;Altenhoff et al 1994) and they are suspected to be present also in the sub-millimetre since, at 0.761 mm on 1993 October 18, the flux value was 67% larger than on the next day: this suggested that the turnover frequency of the synchrotron spectrum may be ≥394 GHz (0.761 mm) (Abada-Simon et al 1995b), but with the usual assumption that the source radius is ≤a/2, we infer that 10 7 ≤ T b < 10 9 K for both the submillimetre and the millimetre emissions (see Table 2). …”

Section: Origin Of Ae Aqr Radio To Sub-millimetre Emissionmentioning

confidence: 99%

First detections of the cataclysmic variable AE Aquarii in the near to far infrared with ISO and IRAS: Investigating the various possible thermal and non-thermal contributions

Abada-Simon

Casares

Evans

et al. 2005

A&A

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Abstract.We have used ISO to observe the Magnetic Cataclysmic Variable AE Aquarii in the previously unexplored range from 4.8 µm up to 170 µm in the framework of a coordinated multi-wavelength campaign from the radio to optical wavelengths. We have obtained for the first time a spectrum between 4.8 and 7.3 µm with ISOCAM and ISOPHOT-P: the major contribution comes from the secondary star spectrum, with some thermal emission from the accretion stream, and possibly some additional cyclotron radiation from the post-shock accretion material close to the magnetised white dwarf. Having reprocessed ISOPHOT-C data, we confirm AE Aqr detection at 90 µm and we have re-estimated its upper limit at 170 µm. In addition, having re-processed IRAS data, we have detected AE Aqr at 60 µm and we have estimated its upper limits at 12, 25, and 100 µm. The literature shows that the time-averaged spectrum of AE Aqr increases roughly with frequency from the radio wavelengths up to ∼761 µm; our results indicate that it seems to be approximately flat between ∼761 and ∼90 µm, at the same level as the 3σ upper limit at 170 µm; and it then decreases from ∼90 µm to ∼7 µm. Thermal emission from dust grains or from a circum-binary disc seems to be very unlikely in AE Aqr, unless such a disc has properties substantially different from those predicted recently. Since various measurements and the usual assumptions on the source size suggest a brightness temperature below 10 9 K at λ ≤ 3.4 mm, we have reconsidered also the possible mechanisms explaining the emission already known from the submillimetre to the radio. The complex average spectrum measured from ∼7 µm to the radio must be explained by emission from a plasma composed of more than one "pure" non-thermal electron energy distribution (usually assumed to be a powerlaw): either a very large volume (diameter ≥ 80 times the binary separation) could be the source of thermal bremsstrahlung which would dominate from ∼10 µm to the ∼millimetre, with, inside, a non-thermal source of synchrotron which dominates in radio; or, more probably, an initially small infrared source composed of several distributions (possibly both thermal, and nonthermal, mildly relativistic electrons) radiates gyro-synchrotron and expands moderately: it requires to be re-energised in order to lead to the observed, larger, radio source of highly relativistic electrons (in the form of several non-thermal distributions) which produce synchrotron.

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Extension of the radio spectrum of AE Aqr to the sub-millimetric range

Cited by 8 publications

References 8 publications

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

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

The diamagnetic blob propeller in AE Aquarii and non-thermal radio to mid-infrared emission

First detections of the cataclysmic variable AE Aquarii in the near to far infrared with ISO and IRAS: Investigating the various possible thermal and non-thermal contributions

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