Mechanisms for High‐Frequency Quasi‐periodic Oscillations in Neutron Star and Black Hole Binaries

Titarchuk, Lev; Lapidus, Iosif; Muslimov, A. G.

doi:10.1086/305642

Cited by 163 publications

(148 citation statements)

References 40 publications

(46 reference statements)

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“…It is quite large, but we observe that a large inner-disk radius is in agreement with the absence of kHz QPOs in the power spectrum density of Cir X-1 (Shirey et al 1996). In fact, kHz QPOs are usually explained as the Keplerian frequency at the inner edge of the disk, near the neutron star surface (Strohmayer et al 1996 ;Miller, Lamb, & Psaltis 1998 ;Stella & Vietri 1999 ;Titarchuk, Lapidus, & Muslimov 1998). The lack of kHz frequencies in the power spectra of Cir X-1 could mean that the inner region of the disk is not present.…”

Section: Possible Presence Of a Magnetic Field Of D4 ] 1010 Gsupporting

confidence: 84%

A Hard Tail in the X‐Ray Broadband Spectrum of Circinus X‐1 at the Periastron: A Peculiar Z Source

Iaria

Burderi

Salvo

et al. 2001

ApJ

100

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We report on the spectral analysis of the peculiar source Cir X-1 observed by the BeppoSAX satellite when the X-ray source was near the periastron. A Ñare lasting D6 ] 103 s is present at the beginning of the observation. The luminosity during the persistent emission is 1 ] 1038 ergs s~1, while during the Ñare it is 2 ] 1038 ergs s~1. We produced broadband (0.1È100 keV) energy spectra during the Ñare and the persistent emission. At low energies the continuum is well Ðtted by a model consisting of Comptonization of soft photons, with a temperature of D0.4 keV, by electrons at a temperature of D1 keV. After the Ñare, a power-law component with photon index D3 is dominant at energies higher than 10 keV. This component contributes D4% of the total luminosity. During the Ñare its addition is not statistically signiÐcant. An absorption edge at D8.4 keV, with optical depth D1, corresponding to the K edge of Fe XXIIIÈFe XXV, and an iron emission line at 6.7 keV are also present. The iron-line energy is in agreement with the ionization level inferred from the absorption edge. The hydrogen column deduced from the absorption edge is D1024 cm~2, 2 orders of magnitude larger than the low-energy absorption measured in this source. We calculated the radius of the region originating the Comptonized seed photons, km. We propose a scenario where (the Wien radius) is the inner disk radius, a R W D 150 R W highly ionized torus surrounds the accretion disk, and a magnetosphere is present up to The R W . absorption edge and the emission line could originate in the photoionized torus, while the Comptonized component originates in an inner region of the disk.

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Section: Possible Presence Of a Magnetic Field Of D4 ] 1010 Gsupporting

confidence: 84%

A Hard Tail in the X‐Ray Broadband Spectrum of Circinus X‐1 at the Periastron: A Peculiar Z Source

Iaria

Burderi

Salvo

et al. 2001

ApJ

100

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“…However, for the characteristic electron temperature (3 keV < ∼ kT e < ∼ 30 keV) and density values ( < ∼ 10 −5 g cm −3 ) of these regions for NS LMXBs, Compton cooling dominates over free-free emission, and the relation between the energy flux per unit surface area of the corona Q cor , the radiation energy density ε(τ), and electron temperature T e is given by (see also Titarchuk et al 1998)…”

Section: Energy Release In the Neutron Star Transition Layermentioning

confidence: 99%

On the stability of the thermal Comptonization index in neutron star low-mass X-ray binaries in their different spectral states

Farinelli¹,

Titarchuk²

2010

A&A

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Context. Most of the spectra of neutron star low-mass X-ray binaries (NS LMXBs), whether they are persistent or transient, are characterized by the presence of a strong thermal Comptonization bump, which is thought to originate in the transition layer (TL) between the accretion disk and the NS surface. The observable quantities that characterize this component, which is dominating the emission below 30 keV, are the spectral index α and the rollover energy, both related to the electron temperature and optical depth of the plasma. Aims. Starting from observational results on a sample of NS LMXBs in different spectral states, we formulate the problem of X-ray spectral formation in the TL of these sources. We predict a stability of the thermal Comptonization spectral index in different spectral states if the energy release in the TL is much higher than the intercepted flux coming from the accretion disk. Methods. We use an equation for the energy balance and the radiative transfer diffusion equation for a slab geometry in the TL to derive a formula for the thermal Comptonization index α. We show that in this approximation the TL electron temperature kT e and optical depth τ 0 can be written as a function of the energy flux from the disk intercepted by the corona (TL) and that in the corona itself, Q disk /Q cor . Because the spectral index α depends on kT e and τ 0 , this in turn leads to a relation α = f (Q disk /Q cor ), with α ∼ 1 when Q disk /Q cor 1. Results. We show that the observed spectral index α for the sample of sources here considered lies in a belt around 1 ± 0.2 apart for the case of GX 354-0. Comparing our theoretical predictions with observations, we claim that this result, which is consistent with the condition Q disk /Q cor 1, can give us constraints on the accretion geometry of these systems, an issue that seems difficult to be solved with only the spectral analysis method.

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“…On the theoretical side, there were papers considering the importance of the angle at which you view the sources (Kuulker & van der Klis 1996); on rotational splitting of frequencies (Titarchuk & Muslimov 1997); and on the period of the last stable orbit around a star as a function of its mass, which (after you have made the proper relativistic corrections) can be used in combination with gravitational redshift to solve for both mass and radius of the neutron star. Kaaret et al (1997) obtain and km for 4U 1636Ϫ536, on the as-2 ‫ע‬ 0.1 M R ϭ 9.6 , sumption that a 4.2 keV spectral feature is redshifted Fe xxv.…”

Section: X-raysmentioning

confidence: 99%

Astrophysics in 1997

Trimble¹,

McFadden²

1998

PUBL ASTRON SOC PAC

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ABSTRACT. Martian marvels, a gamma-ray burster with a redshift, Galileo converses with Ganymede, a record galactic redshift of 4.92, and much else. Fiscal 1997 was definitely an exciting year for astronomers. We have tried hard to hit all the obvious highlights, but also to report more gradual progress on traditional problems of understanding planets, stars, galaxies, and the universe. Though the year was saddened by the loss of many valued colleagues, we nevertheless indulge in occasional soupçons of frivolity.

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Mechanisms for High‐Frequency Quasi‐periodic Oscillations in Neutron Star and Black Hole Binaries

Cited by 163 publications

References 40 publications

A Hard Tail in the X‐Ray Broadband Spectrum of Circinus X‐1 at the Periastron: A Peculiar Z Source

A Hard Tail in the X‐Ray Broadband Spectrum of Circinus X‐1 at the Periastron: A Peculiar Z Source

On the stability of the thermal Comptonization index in neutron star low-mass X-ray binaries in their different spectral states

Astrophysics in 1997

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