Theory of quasi-spherical accretion in X-ray pulsars
By N. Shakura, K. Postnov, A. Kochetkova, L. Hjalmarsdotter. 2011
190 citations recorded by the source corpus.
A theoretical model for quasi-spherical subsonic accretio n onto slowly rotating magnetized neutron stars is constructed. In this model the accr eting matter subsonically settles down onto the rotating magnetosphere forming an extended quasi-static shell. This shell mediates the angular momentum removal from the rotating neutron star magnetosphere during spin-down episodes by large-scale convective motions. The accretion rate through the shell is determined by the abilit y of the plasma to enter the magnetosphere. The settling regime of accretion can be realized for moderate accretion rates ˙ M< ˙ M∗≃ 4× 10 16 g/s. At higher accretion rates a free-fall gap above the neutron star magnetosphere appears due to rapid Compton cooling, and accretion becomes highly non-stationary. From observations of the spin-up/spin-down rates (the angular rotation frequency derivative ˙ ω ∗ , and∂ ˙ ω ∗ /∂ ˙ M near the torque reversal) of X-ray pulsars with known orbital periods, it is possible to d etermine the main dimensionless parameters of the model, as well as to estimate the magnetic field of the neutron star. We illustrate the model by determining these parameters for three wind-fed X-ray pulsars GX 301-2, Vela X-1, and GX 1+4. The model explains both the spin-up/spin-down of the pulsar frequency on large time-scales and the irregular short-term frequency fluctuations, which can correlate or a nti-correlate with the Xray flux fluctuations in di fferent systems. It is shown that in real pulsars an almost iso-angular-momentum rotation law withω∼ 1/R 2 , due to strongly anisotropic radial turbulent motions sustained by large-scale convectio n, is preferred.
Subfields: Astronomy and Astrophysics, Geophysics
View Paper: https://www.semanticscholar.org/paper/aa50d568a3d32b982cbc3f72d97e08b5297c4208
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In Astronomy and Astrophysics
Citations in the corpus
- High-mass X-ray binaries in the Milky Way (2013, background): “Such spectral feature would, indeed, indicate a NS magnetic field as low as ∼1012 G. 4.4 Cooling Switch A different mechanism to halt the mass accretion flow in sgHMXBs and SFXTs was proposed by Shakura et al. (2012).”
- Cyclotron lines in highly magnetized neutron stars (2018, background): “Similar models (some also for the case of wind accretion) have been presented by Wang (1987), Lovelace et al. (1995), Kluźniak & Rappaport (2007), Postnov et al. (2011), Shakura et al. (2012), Shi et al. (2015), Parfrey et al. (2016).”