C. Busschaert

CEA DAM Île-de-France

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ÉF

É. Falize

Commissariat à l'Énergie Atomique et aux Énergies Alternatives

C. Michaut

Lagrange Laboratory

M. Mouchet

Université Paris Cité

J. M. Bonnet-Bidaud

Astrophysique, Instrumentation et Modélisation

M. Kœnig

École Polytechnique

B. Loupias

Commissariat à l'Énergie Atomique et aux Énergies Alternatives

Roman Yurchak

Université Paris-Saclay

L. Van Box Som

CEA DAM Île-de-France

A. Ravasio

École Polytechnique

A. Ciardi

Sorbonne Université

Cooperative Institutions

Centre National de la Recherche Scientifique

Commissariat à l'Énergie Atomique et aux Énergies Alternatives

Sorbonne Université

École Polytechnique

Laboratoire pour l'utilisation des lasers intenses

Osaka University

Université Paris Sciences et Lettres

University of Oxford

CEA Paris-Saclay

University of Michigan–Ann Arbor

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Quasi-periodic oscillations in accreting magnetic white dwarfs

Astronomy and Astrophysics (2015)

J. M. Bonnet-Bidaud M. Mouchet C. Busschaert É. Falize C. Michaut

Quasi-periodic oscillations (QPOs) are observed in the optical flux of some polars with typical periods of 1 to 3 s but none have been observed yet in X-rays where a significant part of the accreting energy is released. QPOs are expected and predicted from shock oscillations. Most of the polars have been observed by the XMM-Newton satellite. We made use of the homogeneous set of observations of the polars by XMM-Newton to search for the presence of QPOs in the (0.5-10 keV) energy range and to set significant upper limits for the brightest X-ray polars. We extracted high time-resolution X-ray light curves by taking advantage of the 0.07 sec resolution of the EPIC-PN camera. Among the 65 polars observed with XMM-Newton from 1998 to 2012, a sample of 24 sources was selected on the basis of their counting rate in the PN instrument to secure significant limits. We searched for QPOs using Fast Fourier Transform (FFT) methods and defined limits of detection using statistical tools. Among the sample surveyed, none shows QPOs at a significant level. Upper limits to the fractional flux in QPOs range from 7% to 71%. These negative results are compared to the detailed theoretical predictions of numerical simulations based on a 2D hydrodynamical code presented in Paper II. Cooling instabilities in the accretion column are expected to produce shock quasi-oscillations with a maximum amplitude reaching ~ 40% in the bremsstrahlung (0.5-10 keV) X-ray emission and ~ 20% in the optical cyclotron emission. The absence of X-ray QPOs imposes an upper limit of ~ (5-10) g.cm-2.s-1 on the specific accretion rate but this condition is found inconsistent with the value required to account for the amplitudes and frequencies of the observed optical QPOs. This contradiction outlines probable shortcomings with the shock instability model.

10.1051/0004-6361/201425482

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Citations (22)

Accretion shock in polars . Numerical and experimental simulations

Memorie della Societa Astronomica Italiana (2012)

C. Michaut É. Falize C. Busschaert B. Loupias A. Ravasio

Intermediate polar

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Laboratory radiative accretion shocks on GEKKO XII laser facility for POLAR project

arXiv (Cornell University) (2018)

L. Van Box Som É. Falize M. Kœnig Y. Sakawa B. Albertazzi

A new target design is presented to model high-energy radiative accretion shocks in polars. In this paper, we present the experimental results obtained on the GEKKO XII laser facility for the POLAR project. The experimental results are compared with 2D FCI2 simulations to characterize the dynamics and the structure of plasma flow before and after the collision. The good agreement between simulations and experimental data confirm the formation of a reverse shock where cooling losses start modifying the post-shock region. With the multi-material structure of the target, a hydrodynamic collimation is exhibited and a radiative structure coupled with the reverse shock is highlighted in both experimental data and simulations. The flexibility on the laser energy produced on GEKKO XII, allowed us to produce high-velocity flows and study new and interesting radiation hydrodynamic regimes between those obtained on the LULI2000 and Orion laser facilities.

Radiative Cooling

10.48550/arxiv.1804.02714

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Laboratory radiative accretion shocks on GEKKO XII laser facility for POLAR project

High Power Laser Science and Engineering (2018)

L. Van Box Som É. Falize M. Kœnig Y. Sakawa B. Albertazzi

A new target design is presented to model high-energy radiative accretion shocks in polars. In this paper, we present the experimental results obtained on the GEKKO XII laser facility for the POLAR project. The experimental results are compared with 2D FCI2 simulations to characterize the dynamics and the structure of plasma flow before and after the collision. The good agreement between simulations and experimental data confirms the formation of a reverse shock where cooling losses start modifying the post-shock region. With the multi-material structure of the target, a hydrodynamic collimation is exhibited and a radiative structure coupled with the reverse shock is highlighted in both experimental data and simulations. The flexibility of the laser energy produced on GEKKO XII allowed us to produce high-velocity flows and study new and interesting radiation hydrodynamic regimes between those obtained on the LULI2000 and Orion laser facilities.

Radiative Cooling

10.1017/hpl.2018.32

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Citations (6)

Laboratory analogue of a supersonic accretion column in a binary star system

Nature Communications (2016)

J. E. Cross G. Gregori J. M. Foster Peter W. Graham J. M. Bonnet-Bidaud

Astrophysical flows exhibit rich behaviour resulting from the interplay of different forms of energy-gravitational, thermal, magnetic and radiative. For magnetic cataclysmic variable stars, material from a late, main sequence star is pulled onto a highly magnetized (B>10 MG) white dwarf. The magnetic field is sufficiently large to direct the flow as an accretion column onto the poles of the white dwarf, a star subclass known as AM Herculis. A stationary radiative shock is expected to form 100-1,000 km above the surface of the white dwarf, far too small to be resolved with current telescopes. Here we report the results of a laboratory experiment showing the evolution of a reverse shock when both ionization and radiative losses are important. We find that the stand-off position of the shock agrees with radiation hydrodynamic simulations and is consistent, when scaled to AM Herculis star systems, with theoretical predictions.

Intermediate polar

10.1038/ncomms11899

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Citations (17)

Constraints on QPOs in accreting magnetic white dwarfs from XMM observations and simulations

The X-ray Universe 2014 (2014)

J. Bonnet-Bidaud M. Mouchet C. Busschaert É. Falize C. Michaut

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Fast quasi-periodic oscillations in the eclipsing polar VV Puppis from VLT and XMM-Newton observations

Astronomy and Astrophysics (2019)

J. M. Bonnet-Bidaud M. Mouchet É. Falize L. Van Box Som C. Busschaert

We present high time resolution optical photometric data of the polar VV Puppis obtained simultaneously in three filters ( u ′, HeII λ 4686, r ′) with the ULTRACAM camera mounted at the ESO-VLT telescope. An analysis of a long 50 ks XMM-Newton observation of the source, retrieved from the database, is also provided. Quasi-periodic oscillations (QPOs) are clearly detected in the optical during the source bright phase intervals when the accreting pole is visible, confirming the association of the QPOs with the basis of the accretion column. QPOs are detected in the three filters at a mean frequency of ∼0.7 Hz with a similar amplitude ∼1%. Mean orbitally-averaged power spectra during the bright phase show a rather broad excess with a quality factor Q = ν /Δ ν = 5−7 but smaller data segments commonly show a much higher coherency with Q up to 30. The X-ray Multi-mirror Mission XMM (0.5–10 keV) observation provides the first accurate estimation of the hard X-ray component with a high kT ∼ 40 keV temperature and confirms the high extreme ultraviolet (EUV)-soft/hard ratio in the range of 4−15 for VV Pup. The detailed X-ray orbital light curve displays a short Δ ϕ ≃ 0.05 ingress into self-eclipse of the active pole, indicative of an accretion shock height of ∼75 km. No significant X-ray QPOs are detected with an amplitude upper limit of ∼30% in the range 0.1–5 Hz. Detailed hydrodynamical numerical simulations of the post-shock accretion region with parameters consistent with VV Pup demonstrate that the expected frequencies from radiative instability are identical for X-rays and optical regime at values ν ∼ 40–70 Hz, more than one order magnitude higher than observed. This confirms previous statements suggesting that present instability models are unable to explain the full QPO characteristics within the parameters commonly known for polars.

Eclipse

10.1051/0004-6361/201935741

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Citations (2)

High-energy density laboratory astrophysics studies of accretion shocks in magnetic cataclysmic variables

High Energy Density Physics (2011)

É. Falize A. Ravasio B. Loupias A. Dizière C. Grégory

Cataclysmic variable star

Intermediate polar

Accretion disc

10.1016/j.hedp.2011.10.001

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Citations (30)

Numerical modelling of the accretion column in magnetic cataclysmic variables

C. Busschaert C. Michaut É. Falize B. Loupias A. Ravasio

Intermediate polar

Cataclysmic variable star

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Quasi-periodic oscillations in accreting magnetic white dwarfs II. The asset of numerical modelling for interpreting observations

arXiv (Cornell University) (2015)

C. Busschaert É. Falize C. Michaut J. M. Bonnet-Bidaud M. Mouchet

Magnetic cataclysmic variables are close binary systems containing a strongly magnetized white dwarf that accretes matter coming from an M-dwarf companion. High-energy radiation coming from those objects is emitted from the accretion column close to the white dwarf photosphere at the impact region. Its properties depend on the characteristics of the white dwarf and an accurate accretion column model allows the properties of the binary system to be inferred, such as the white dwarf mass, its magnetic field, and the accretion rate. We study the temporal and spectral behaviour of the accretion region and use the tools we developed to accurately connect the simulation results to the X-ray and optical astronomical observations. The radiation hydrodynamics code Hades was adapted to simulate this specific accretion phenomena. Classical approaches were used to model the radiative losses of the two main radiative processes: bremsstrahlung and cyclotron. The oscillation frequencies and amplitudes in the X-ray and optical domains are studied to compare those numerical results to observational ones. Different dimensional formulae were developed to complete the numerical evaluations. The complete characterization of the emitting region is described for the two main radiative regimes: when only the bremsstrahlung losses and when both cyclotron and bremsstrahlung losses are considered. The effect of the non-linear cooling in- stability regime on the accretion column behaviour is analysed. Variation in luminosity on short timescales (~ 1 s quasi-periodic oscillations) is an expected consequence of this specific dynamic. The importance of secondary shock instability on the quasi-periodic oscillation phenomenon is discussed. The stabilization effect of the cyclotron process is confirmed by our numerical simulations, as well as the power distribution in the various modes of oscillation.

Intermediate polar

Oscillation (cell signaling)

Photosphere

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Citations (1)