On the area of accretion curtains from fast aperiodic time variability of the intermediate polar EX Hya

Семена, А. Н.; Revnivtsev, M.; Buckley, D.; Kotze, M.; Khabibullin, Ildar; Breytenbach, H.; Gulbis, A. A. S.; Coppejans, Rocco; Potter, S.

doi:10.1093/mnras/stu897

Cited by 13 publications

(14 citation statements)

References 73 publications

(83 reference statements)

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“…Using the specific accretion rate of a = 3 g cm −2 s −1 and f = 1.6 × 10 −4 , as recently obtained by Semena et al (2014), resulted in both H-and He-like fluxes overestimated by more than an order of magnitude. Fujimoto & Ishida (1997) found that their cooling flow model fit the line ratios of high-Z ions (Z > 14), assuming that the bottom of the accretion column has a temperature kT B = 0.65 keV, preventing any cooling below this temperature.…”

Section: The Isobaric Cooling Flow Derivation Of a Physically-based mentioning

confidence: 73%

“…If we use M WD = 0.79 M , R WD = 7×10 8 cm, h sh = 0.1 × R WD , and R in = 2.7 × R WD (Revnivtsev et al 2011;Semena et al 2014), we have v ff = 4000 km s −1 . Using the strong shock condition kT shock = 3µm p v 2 ff /16, we find that kT shock ∼ 19 keV.…”

Section: Ex Hyamentioning

confidence: 99%

“…We explored a range of specific accretion rates, a, between 0.2 and 2.0 g s −1 cm −2 , resulting in a range of shock temperatures from 15.9 to 21.3 keV. The models use R in = 2.7 R WD (Revnivtsev et al 2011;Semena et al 2014). Tables 1 and 2 list the resulting fluxes and line ratios from this model (Model B), respectively, with a shock temperature of 19.7 keV, which matches the shock temperature derived from the WD mass of 0.79 M , a specific accretion rate of 0.6 g s −1 cm −2 , and an accretion ratė M = 1.74 × 10 −11 M yr −1 .…”

Section: Magnetic Dipole Geometrymentioning

confidence: 99%

“…In intermediate polars (IPs), the WD has a magnetic field strong enough to disrupt the accretion disk at the Alfvén radius R in (Revnivtsev et al 2011;Semena et al 2014), where magnetic pressure balances the ram pressure of the accretion flow. The WD's magnetic field then channels the material from the inner disk toward the magnetic poles.…”

Section: Introductionmentioning

confidence: 99%

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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: The Isobaric Cooling Flow Derivation Of a Physically-based mentioning

confidence: 73%

Section: Ex Hyamentioning

confidence: 99%

Section: Magnetic Dipole Geometrymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Testing the cooling flow model in the intermediate polar EX Hydrae

Luna

Raymond

Brickhouse

et al. 2015

A&A

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“…On the other hand, Revnivtsev et al (2011) and Semena et al (2014) modeled the break frequency in the power spectrum of stochastic variability and proposed R in =2.7 R W D . Belle et al (2003), Suleimanov et al (2016) and Echevarria et al (2016) also derived small R in using other methods.…”

Section: Introductionmentioning

confidence: 99%

Constraining the Accretion Geometry of the Intermediate Polar EX Hya Using NuSTAR, Swift, and Chandra Observations

Luna

Mukai

Orio

et al. 2018

ApJL

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In magnetically accreting white dwarf, the height above the white dwarf surface where the standing shock is formed is intimately related with the accretion rate and the white dwarf mass. However, it is difficult to measure. We obtained new data with NuSTAR and Swift that together with archival Chandra data allow us to constrain the height of the shock in the intermediate polar EX Hya. We conclude that the shock has to form at least at a distance of about one white dwarf radius from the surface in order to explain the weak Fe Kα 6.4 keV line, the absence of a reflection hump in the high energy continuum and the energy dependence of the white dwarf spin pulsed fraction. Additionally, the NuSTAR data allowed us to measure the true, uncontaminated hard X-ray (12-40 keV) flux, whose measurement was contaminated by the nearby galaxy cluster Abell 3528 in non-imaging X-ray instruments.

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Magnetic Fields of Neutron Stars in X-Ray Binaries

Revnivtsev

Mereghetti

2016

Space Sciences Series of ISSI

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A substantial fraction of the known neutron stars resides in X-ray binaries -systems in which one compact object accretes matter from a companion star. Neutron stars in X-ray binaries have magnetic fields among the highest found in the Universe, spanning at least the range from ∼ 10 8 to several 10 13 G. The magnetospheres around these neutron stars have a strong influence on the accretion process, which powers most of their emission. The magnetic field intensity and geometry, are among the main factors responsible for the large variety of spectral and timing properties observed in the X-ray energy range, making these objects unique laboratories to study the matter behavior and the radiation processes in magnetic fields unaccessible on Earth. In this paper we review the main observational aspects related to the presence of magnetic fields in neutron star X-ray binaries and some methods that are used to estimate their strength.

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On the area of accretion curtains from fast aperiodic time variability of the intermediate polar EX Hya

Cited by 13 publications

References 73 publications

Testing the cooling flow model in the intermediate polar EX Hydrae

Testing the cooling flow model in the intermediate polar EX Hydrae

Constraining the Accretion Geometry of the Intermediate Polar EX Hya Using NuSTAR, Swift, and Chandra Observations

Magnetic Fields of Neutron Stars in X-Ray Binaries

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