Intermediate polars in the <i>Swift</i>/BAT survey:  
spectra and white dwarf masses

Brunschweiger, Jorg; Greiner, J.; Ajello, M.; Osborne, J. P.

doi:10.1051/0004-6361/200811285

Cited by 71 publications

(117 citation statements)

References 42 publications

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“…Using the strong shock condition kT shock = 3µm p v 2 ff /16, we find that kT shock ∼ 19 keV. Mukai et al (2003) obtained a good fit to a short Chandra HETG observation with a shock temperature of 20 keV, Yuasa et al (2010) obtained kT shock = 12.7 +0.9 −0.9 keV from their fit to Suzaku data, Brunschweiger et al (2009) fit of Swift/BAT data yielded kT shock = 19.4 +4.4 −4.4 keV, whereas Fujimoto & Ishida (1997) obtained kT shock = 15.4 +5.3 −2.6 keV from the line ratios in the ASCA spectrum.…”

Section: Ex Hyamentioning

confidence: 77%

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: Ex Hyamentioning

confidence: 77%

Testing the cooling flow model in the intermediate polar EX Hydrae

Luna

Raymond

Brickhouse

et al. 2015

A&A

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“…Later Brunschweiger et al (2009) confirmed this conclusion by estimating the WD mass in GK Per in quiescence. The difference between the estimates of the WD mass in EX Hya obtained using the RXTE observations (0.5 M , Suleimanov et al 2005) and from the optical observations (0.79 M , Beuermann & Reinsch 2008) was also attributed to a small magnetospheric radius in this system (∼2.7 WD radii; see e.g., Revnivtsev et al 2011).…”

Section: Introductionmentioning

confidence: 76%

“…GK Per is a bright hard X-ray source during the outbursts and it was observed by many X-ray observatories including EXOSAT (Watson et al 1985;Norton et al 1988), Ginga (Ishida et al 1992), ASCA (Ezuka & Ishida 1999), RXTE (Hellier et al 2004;Suleimanov et al 2005), XMM-Newton (Vrielmann et al 2005;Evans & Hellier 2007), Chandra (Mauche 2004), INTEGRAL (Barlow et al 2006;Landi et al 2009), and Swift/BAT (Brunschweiger et al 2009). Some of these observations were also used to estimate the WD mass.…”

Section: Gk Permentioning

confidence: 99%

“…Some of these models were used to estimate the WD masses in several intermediate polars and polars (Cropper et al 1998(Cropper et al , 1999Ramsay 2000;Revnivtsev et al 2004b;Suleimanov et al 2005;Falanga et al 2005;Brunschweiger et al 2009;Yuasa et al 2010;Hayashi & Ishida 2014b). However, in all these models the accreting plasma was assumed to fall from infinity whereas in reality the magnetospheric radius could be small enough (a few WD radii) to break this assumption.…”

Section: Introductionmentioning

confidence: 99%

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GK Persei and EX Hydrae: Intermediate polars with small magnetospheres

Suleimanov

Doroshenko

Ducci

et al. 2016

A&A

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Observed hard X-ray spectra of intermediate polars are determined mainly by the accretion flow velocity at the white dwarf surface, which is normally close to the free-fall velocity. This allows us to estimate the white dwarf masses as the white dwarf mass-radius relation M − R and the expected free-fall velocities at the surface are well known. This method is widely used. However, derived white dwarf masses M can be systematically underestimated because the accretion flow is stopped at, and re-accelerates from, the magnetospheric boundary R m and, therefore, its velocity at the surface is lower than free fall. To avoid this problem, we computed a two-parameter set of model hard X-ray spectra, which allows us to constrain a degenerate M − R m dependence. Previous works showed that power spectra of accreting X-ray pulsars and intermediate polars exhibit breaks at frequencies corresponding to Keplerian frequencies at the magnetospheric boundary. Therefore, the break frequency ν b in an intermediate polar power spectrum gives another relation in the M − R m plane. The intersection of the two dependences allows us, therefore, to determine the white dwarf mass and magnetospheric radius simultaneously. To verify the method, we analysed the archival Suzaku observation of EX Hya, obtaining M/M = 0.73 ± 0.06 and R m /R = 2.6 ± 0.4, which is consistent with the values determined by other authors. Subsequently, we applied the same method to a recent NuSTAR observation of another intermediate polar GK Per performed during an outburst and found M/M = 0.86 ± 0.02 and R m /R = 2.8 ± 0.2. The long duration observations of GK Per in quiescence performed by Swift/BAT and INTEGRAL observatories indicate increase of magnetosphere radius R m at lower accretion rates.

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“…They show modulation of the X-ray and/or optical light curves at P spin and the appearance of the beat period (where 1/P beat = 1/P spin -1/P orb ) or its sidebands. The hardest X-ray emission comes from the cooling post-shock region of IPs rather than Polars, since the strong magnetic field of Polars causes the cyclotron cooling to dominate the cooling post-shock region suppressing the Bremsstrahlung emission ( [1]; [2]; [3]; [4]; [5]; ). source is suggested to have an extended bulge on the outer accretion disc and extended/overflowing material originating from the hot spot.…”

Section: Introductionmentioning

confidence: 99%

Phase Resolved X-Ray Spectral Analysis of Intermediate Polars EX Hya and FO Aqr

Pekön

Balman

2014

EPJ Web of Conferences

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Abstract. Intermediate Polars (IPs): EX Hya and FO Aqr whichs are a subclass of Cataclysmic Variables (CVs) where a white dwarf with magnetic field strength of about 1-10 MG accretes material from a main sequence companion through a truncated disc. In this talk we present orbital and spin phase-resolved X-ray spectroscopy of EX Hya and orbital phase-resolved X-ray spectroscopy of FO Aqr. We utilize XMM-Newton archive data of these objects for analysis. We investigate the change of the source spectrum over the spin and orbital periods. This analysis enhances our understanding about the accretion structure in these systems, temperature and composition of the X-ray emitting region together with the structure of the outer accretion disc and absorption in the system

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Intermediate polars in the Swift/BAT survey: spectra and white dwarf masses

Cited by 71 publications

References 42 publications

Testing the cooling flow model in the intermediate polar EX Hydrae

Testing the cooling flow model in the intermediate polar EX Hydrae

GK Persei and EX Hydrae: Intermediate polars with small magnetospheres

Phase Resolved X-Ray Spectral Analysis of Intermediate Polars EX Hya and FO Aqr

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