An instability associated with a magnetosphere-disk interaction

Spruit, H. C.; Taam, Ronald E.

doi:10.1086/172162

Cited by 200 publications

(324 citation statements)

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“…If r m remains too close to r co so that matter cannot be ejected from the system, then an accretion disk different than the The definition of r m used in this paper is the same as in Spruit & Taam (1993) whereas the classical expression of r m (Pringle & Rees 1972), obtained by equating the gas and magnetic pressures, gives a somewhat larger value of about 500 km, which would further strengthen the argument presented here. standard geometrically thin and optically thick ShakuraSunyaev type needs to develop (scenario B).…”

Section: Accretion Flow Geometrysupporting

confidence: 58%

“…Indeed the spectra analyzed by Kajava et al (Bult & van der Klis 2014). In both cases an instability arising from a trapped disk (Spruit & Taam 1993;D'Angelo & Spruit 2010 has been proposed to be at the origin of this phenomenon. Such a disk model has also been discussed to explain a strikingly similar 1 Hz modulation observed in another accreting millisecond pulsar (NGC 6440 X-2; see Patruno & D'Angelo 2013).…”

Section: Observational Constraints On Accretion Flow Geometrymentioning

confidence: 96%

“…To enter a strong propeller regime with matter expelled from the system, r m needs to be larger than r co by at least a factor 1.3 » so that the gas can gain enough kinetic energy to reach the escape velocity (Spruit & Taam 1993). If a strong propeller (Illarionov & Sunyaev 1975;Romanova et al 2005;Ustyugova et al 2006) is operating in the system then the very-low luminosities we observe are not due to an extremely low mass flow in the disk, but instead reflect the fact that only a tiny (poorly constrained) fraction of the mass actually falls onto the neutron star surface, generating X-rays (see also Lasota et al 1999 where a similar scenario was proposed for the dwarf nova WZ-Sge).…”

Section: Accretion Flow Geometrymentioning

confidence: 99%

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The Reflares and Outburst Evolution in the Accreting Millisecond Pulsar Sax J1808.4–3658: A Disk Truncated Near Co-Rotation?

Patruno

Maitra

Curran

et al. 2016

ApJ

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The accreting millisecond X-ray pulsar SAX J1808.4-3658 shows peculiar low luminosity states known as "reflares" after the end of the main outburst. During this phase the X-ray luminosity of the source varies by up to three orders of magnitude in less than 1-2 days. The lowest X-ray luminosity observed reaches a value of 10 erg s 32 1 -, only a factor of a few brighter than its typical quiescent level. We investigate the 2008 and 2005 reflaring state of SAX J1808.4-3658 to determine whether there is any evidence for a change in the accretion flow with respect to the main outburst. We perform a multiwavelength photometric and spectral study of the 2005 and 2008 reflares with data collected during an observational campaign covering the near-infrared, optical, ultra-violet and X-ray band. We find that the NIR/optical/UV emission, expected to come from the outer accretion disk, shows variations in luminosity over an order of magnitude. The corresponding X-ray luminosity variations are instead much deeper, spanning about 2-3 orders of magnitude. The X-ray spectral state observed during the reflares does not change substantially with X-ray luminosity, indicating a rather stable configuration of the accretion flow. We investigate the most likely configuration of the innermost regions of the accretion flow and we infer an accretion disk truncated at or near the co-rotation radius. We interpret these findings as due to either a strong outflow (due to a propeller effect) or a trapped disk (with limited/no outflow) in the inner regions of the accretion flow.

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Section: Accretion Flow Geometrysupporting

confidence: 58%

Section: Observational Constraints On Accretion Flow Geometrymentioning

confidence: 96%

Section: Accretion Flow Geometrymentioning

confidence: 99%

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The Reflares and Outburst Evolution in the Accreting Millisecond Pulsar Sax J1808.4–3658: A Disk Truncated Near Co-Rotation?

Patruno

Maitra

Curran

et al. 2016

ApJ

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“…In the propeller regime, the centrifugal force plays the dominant role in this interaction. The centrifugal barrier inhibits accretion onto the rapidly rotating star; however, accretion can proceed in episodic bursts through the episodic accretion instability developed in [17][18][19]. The episodic accretion instability proceeds as follows:…”

Section: Episodic Accretion Onto the Starmentioning

confidence: 99%

MHD Simulations of Magnetized Stars in the Propeller Regime of Accretion

Lii

Romanova

Lovelace

2014

EPJ Web of Conferences

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Abstract. Accreting magnetized stars may be in the propeller regime of disc accretion in which the angular velocity of the stellar magnetosphere exceeds that of the inner disc. In these systems, the stellar magnetosphere acts as a centrifugal barrier and inhibits matter accretion onto the rapidly rotating star. Instead, the matter accreting through the disc accumulates at the disc-magnetosphere interface where it picks up angular momentum and is ejected from the system as a wide-angled outflow which gradually collimates at larger distances from the star. If the ejection rate is lower than the accretion rate, the matter will accumulate at the boundary faster than it can be ejected; in this case, accretion onto the star proceeds through an episodic accretion instability in which the episodes of matter accumulation are followed by a brief episode of simultaneous ejection and accretion of matter onto the star. In addition to the matter dominated wind component, the propeller outflow also exhibits a well-collimated, magnetically-dominated Poynting jet which transports energy and angular momentum away from the star. The propeller mechanism may explain some of the weakly-collimated jets and winds observed around some T Tauri stars as well as the episodic variability present in their light curves. It may also explain some of the quasi-periodic variability observed in cataclysmic variables, millisecond pulsars and other magnetized stars.

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“…Many authors have derived the spin-down rate of propeller phase by assuming that the infalling material is ejected with the corotation velocity at the magnetospheric radius when the magnetospheric radius is larger than the corotation radius (Wang & Robertson 1985;Dai, Liu & Li 2006;Jiang & Li 2005). Besides, a large number of authors (see, e.g., Spruit & Taam 1993;Rappaport et al 2004;D'Angelo & Spruit 2010, 2012 have investigated the spin-down rate of NS accreting from a disk in a NS HMXB. Romanova et al (2013) have studied accretion onto a star in the propeller regime by magnetohydrodynamic simulations.…”

Section: Introductionmentioning

confidence: 99%

Exploration of spin-down rate of neutron stars in high-mass X-ray binaries

Dai¹,

Liu²,

Li³

2016

Mon. Not. R. Astron. Soc.

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We use the evolutionary population synthesis method to investigate the statistical properties of the wind-fed neutron star (NS) compact (P orb < 10 days) high-mass X-ray binaries (HMXBs) in our Galaxy, based on different spin-down models. We find that the spin-down rate in the supersonic propeller phase given by assuming that the surrounding material is treated as forming a quasi-static atmosphere or by assuming that the characteristic velocity of matter and the typical Alfvén velocity of material in the magnetospheric boundary layer are comparable to the sound speed in the external medium is too low to produce the observed number of compact HMXBs. We also find that the models suggested by assuming that the infalling material is ejected with the corotation velocity at the magnetospheric radius when the magnetospheric radius is larger than the corotation radius and by simple integration of the magnetic torque over the magnetosphere with a larger spin-down rate than that given by Davies & Pringle (1981) or Illarionov & Sunyaev (1975) can predict a reasonable number of observed wind-fed NS compact HMXBs. Our calculated results indicate that subsonic propeller phase may not exist at all by comparing with the observed particular distributions of wind-fed NS compact HMXBs in the P s − P orb diagram. However, the spin-down rate suggested by Wang & Robertson (1985); Dai, Liu & Li (2006);Jiang & Li (2005) and that given by Davidson & Ostriker (1973) both seem reasonable to produce the observed distribution of wind-fed NS compact HMXBs in the P s − P orb diagram. We cannot find which spin-down rate seems more reasonable from our calculations.

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An instability associated with a magnetosphere-disk interaction

Cited by 200 publications

References 0 publications

The Reflares and Outburst Evolution in the Accreting Millisecond Pulsar Sax J1808.4–3658: A Disk Truncated Near Co-Rotation?

The Reflares and Outburst Evolution in the Accreting Millisecond Pulsar Sax J1808.4–3658: A Disk Truncated Near Co-Rotation?

MHD Simulations of Magnetized Stars in the Propeller Regime of Accretion

Exploration of spin-down rate of neutron stars in high-mass X-ray binaries

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