Are there three peaks in the power spectra of GX 339−4 and Cyg X-1?

By Michael A. Nowak. 2000

167 citations recorded by the source corpus.

Among the variability behaviours exhibited by neutron star systems are the so-called ‘horizontal branch oscillations’ (HBO, with frequencies ≈50 Hz), the ‘lower-frequency kHz quasi-periodic oscillation’ (QPO) and the ‘upper-frequency kHz QPO’, with the latter two features being separated in frequency by an amount comparable to, but varying slightly from, the suspected spin-frequency of the neutron star. Recently, Psaltis, Belloni & van der Klis have suggested that there exists a correlation between these three frequencies that, when certain identifications of variability features are made, even encompasses black hole sources. We consider this hypothesis by reanalysing a set of GX 339−4 observations. The power spectral density (PSD) constructed from a composite of seven separate, but very similar, observations shows evidence for three broad peaks in the PSD. If the peak frequencies of these features are identified with QPO, then their frequencies approximately fit the correlations suggested by Psaltis, Belloni, & van der Klis. We also reanalyse a Cyg X-1 observation and show that the suggested QPO correlation may also hold, but that complications arise when the QPOs (which, in reality, are fairly broad features) are considered as a function of energy band. These fits suggest the existence of at least three separate, independent physical processes in the accretion flow, a hypothesis that is also supported by consideration of the Fourier frequency-dependent time lags and coherence function between variability in different energy bands. If these variability features have a common origin in neutron star and black hole systems, then ‘beat frequency models’ of kHz QPO in neutron star systems are called into question.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/0fa1cbb77b235a1b0b81cb90e035396462b145a8

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

In Instrumentation

Citations in the corpus

A Unified Description of the Timing Features of Accreting X-Ray Binaries (2002, methodology): “Following Nowak (2000), we describe the power spectra of both neutron-star and black-hole sources by a sum of Lorentzian components, given individually by P (ν) = r2∆ π 1 ∆2 + (ν − ν0)2 , (1) where r is the integrated fractional rms (over −∞ to +∞) of each Lorentzian and ∆ its HWHM.”
X-Ray Properties of Black-Hole Binaries (2006, methodology): “QPOs are generally modeled with Lorentzian profiles, and they are distinguished from broad power peaks using a coherence parameter, Q = ν/FWHM >∼ 2 (Nowak 2000; van der Klis 2005).”
Investigating a fluctuating-accretion model for the spectral-timing properties of accreting black hole systems (2005, background): “…fluctuations can still be correct but additional assumptions need to be made, for example, assuming that a few annuli have much enhanced variability power will certainly produce a bumpy PSD and might reproduce the steps in the lag spectra, as suggested by Nowak (2000) and also Kotov et al. (2001).”
Long term variability of Cygnus X-1. I. X-ray spectral-temporal correlations in the hard state (2002, methodology): “5 of Nowak 2000).”
Measuring the broad-band power spectra of active galactic nuclei with RXTE (2002, background): “More complex models, consisting of multiple frequency-breaks and a variety of power-spectral slopes, or a number of broad Lorentzians (e.g. Nowak 2000) might also successfully explain the data.”
The evolution of the timing properties of the black-hole transient GX 339-4 during its 2002/2003 outburst (2005, unknown): “The power spectra were then fitted with a combination of Lorentzians (see Nowak 2000; Belloni et al. 2002) using XSPEC v11.”
Evidence for Harmonic Relationships in the High-Frequency Quasi-periodic Oscillations of XTE J1550–564 and GRO J1655–40 (2002, methodology): “Finally, we note that global PDS modeling has been performed successfully for sources in hard X-ray states using multiple Lorentzians (Nowak 2000; Belloni, Psaltis, & van der Klis 2002; Pottschmidt et al. 2002).”
Non‐linear X‐ray variability in X‐ray binaries and active galaxies (2005, methodology): “We originally suggested that models should be con- PSDs of XRBs are better represented as a sum of broad Lorentzians (Nowak, 2000; Belloni, Psaltis & van der Klis, 2002; Pottschmidt et al., 2003). sidered where the longer-term variations precede the shorttime-scale variations, e.g. as in the…”
Modelling the behaviour of accretion flows in X-ray binaries (2007, background): “Instead, it is much better described by a series (generally 4–5) of peaked noise components (Lorentzians), where the peak frequency, width and normalization are free to vary (Psaltis, Belloni & van der Klis 1999; Nowak 2000; Belloni, Psaltis & van der Klis 2002).”