White dwarf masses in intermediate polars observed with the Suzaku satellite

Yuasa, Takayuki; Nakazawa, K.; Makishima, Kazuo; Saitou, Kei; Ishida, M.; Ebisawa, Ken; Mori, Hajime; Yamada, S.

doi:10.1051/0004-6361/201014542

Cited by 93 publications

(192 citation statements)

References 83 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: 74%

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: 74%

Testing the cooling flow model in the intermediate polar EX Hydrae

Luna

Raymond

Brickhouse

et al. 2015

A&A

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“…Using the IP Mass model that Suleimanov et al (2005) applied to 14 CV/IPs, we obtain a mass in excess of 1.3 M ⊙ for IGR J14091-6108, while Suleimanov et al (2005) find masses between 0.50 ± 0.05 M ⊙ (for EX Hya) and 1.00 ± 0.20 M ⊙ (for V1062 Tau). Yuasa et al (2010) also used spectral fitting to estimate white dwarf masses for 17 CV/IPs, and they found masses as high as ∼1.2 M ⊙ for V709 Cas, PQ Gem, and NY Lup. Hailey et al (submitted) fit spectra from several X-ray satellites including NuSTAR for the CV/IP IGR J17303-0601, which has a relatively massive white dwarf.…”

Section: Discussionmentioning

confidence: 99%

Identifying IGR J14091−6108 as a magnetic CV with a massive white dwarf using X-ray and optical observations

Tomsick

Rahoui

Krivonos

et al. 2016

Mon. Not. R. Astron. Soc.

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IGR J14091-6108 is a Galactic X-ray source known to have an iron emission line, a hard X-ray spectrum, and an optical counterpart. Here, we report on X-ray observations of the source with XMM-Newton and NuSTAR as well as optical spectroscopy with ESO/VLT and NOAO/SOAR. In the X-rays, this provides data with much better statistical quality than the previous observations, and this is the first report of the optical spectrum. Timing analysis of the XMM data shows a very significant detection of 576.3 ± 0.6 s period. The signal has a pulsed fraction of 30 ± 3% in the 0.3-12 keV range and shows a strong drop with energy. The optical spectra show strong emission lines with significant variability in the lines and continuum, indicating that they come from an irradiated accretion disk. Based on these measurements, we identify the source as a magnetic Cataclysmic Variable of Intermediate Polar (IP) type where the white dwarf spin period is 576.3 s. The X-ray spectrum is consistent with the continuum emission mechanism being due to thermal Bremsstrahlung, but partial covering absorption and reflection are also required. In addition, we use the IP mass (IPM) model, which suggests that the white dwarf in this system has a high mass, possibly approaching the Chandrasekhar limit.

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“…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%

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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White dwarf masses in intermediate polars observed with the Suzaku satellite

Cited by 93 publications

References 83 publications

Testing the cooling flow model in the intermediate polar EX Hydrae

Testing the cooling flow model in the intermediate polar EX Hydrae

Identifying IGR J14091−6108 as a magnetic CV with a massive white dwarf using X-ray and optical observations

GK Persei and EX Hydrae: Intermediate polars with small magnetospheres

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