Temporal Properties of Cygnus X‐1 during the Spectral Transitions

Cui, Wei; Zhang, S. N.; Focke, W. B.; Swank, J. H.

doi:10.1086/304341

Cited by 180 publications

(253 citation statements)

References 30 publications

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“…In the spirit of the approach chosen here that avoids depending on models for the variability, we label the lower frequency variability component as component 1 and the higher frequency variability component as component 2. Both components shift to higher frequencies as Γ 1 softens (see also Cui et al 1997;Gilfanov et al 1999;Pottschmidt et al 2003;Axelsson et al 2005;Shaposhnikov & Titarchuk 2006;Böck et al 2011). The two components appear to have roughly similar strengths.…”

Section: Energy-independent Evolution Of Psds With Spectral Shapementioning

confidence: 87%

“…The frequency shift of the variability components of the PSDs in the RXTE range with the softening of the source in the hard and intermediate states continues at higher energies (Cui et al 1997;Pottschmidt et al 2006;Cabanac et al 2011) up to ∼200 keV (Torii et al 2011), even though such high energy analyses are rare. The different energy dependence of the components has been previously noted for individual observations, both for the presented energy range and above (Cui et al 1997;Nowak et al 1999a;Pottschmidt et al 2006;Böck et al 2011), but never shown for such a comprehensive data set as presented in this work.…”

Section: Discussion Of Psd Shapesmentioning

confidence: 99%

“…Often considered a prototypical black hole binary, it is frequently used for comparisons with other black hole binaries (e.g, Muñoz-Darias et al 2010) and AGN (Markowitz et al 2003;McHardy et al 2004;Papadakis et al 2009). Although the spectrum of the source is never fully dominated by the disk and the bolometric luminosity changes by a factor of only ∼4 (Cui et al 1997;Shaposhnikov & Titarchuk 2006;Wilms et al 2006, and references therein), Cyg X-1 often undergoes state transitions (e.g., Pottschmidt et al 2003;Wilms et al 2006;Grinberg et al 2013) and is therefore also well suited to study the intermediate states.…”

Section: Introductionmentioning

confidence: 99%

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Long term variability of Cygnus X-1

Grinberg

Pottschmidt

Böck

et al. 2014

A&A

116

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We present the most extensive analysis of Fourier-based X-ray timing properties of the black hole binary Cygnus X-1 to date, based on 12 years of bi-weekly monitoring with RXTE from 1999 to 2011. Our aim is a comprehensive study of timing behavior across all spectral states, including the elusive transitions and extreme hard and soft states. We discuss the dependence of the timing properties on spectral shape and photon energy, and study correlations between Fourier-frequency dependent coherence and time lags with features in the power spectra. Our main results follow. (a) The fractional rms in the 0.125-256 Hz range in different spectral states shows complex behavior that depends on the energy range considered. It reaches its maximum not in the hard state, but in the soft state in the Comptonized tail above 10 keV. (b) The shape of power spectra in hard and intermediate states and the normalization in the soft state are strongly energy-dependent in the 2.1-15 keV range. This emphasizes the need for an energy-dependent treatment of power spectra and a careful consideration of energy-and mass-scaling when comparing the variability of different source types, e.g., black hole binaries and AGN. PSDs during extremely hard and extremely soft states can be easily confused for energies above ∼5 keV in the 0.125-256 Hz range. (c) The coherence between energy bands drops during transitions from the intermediate into the soft state but recovers in the soft state. (d) The time lag spectra in soft and intermediate states show distinct features at frequencies related to the frequencies of the main variability components seen in the power spectra and show the same shift to higher frequencies as the source softens. Our results constitute a template for other sources and for physical models for the origin of the X-ray variability. In particular, we discuss how the timing properties of Cyg X-1 can be used to assess the evolution of variability with spectral shape in other black hole binaries. Our results suggest that none of the available theoretical models can explain the full complexity of X-ray timing behavior of Cyg X-1, although several ansatzes with different physical assumptions are promising.

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Section: Energy-independent Evolution Of Psds With Spectral Shapementioning

confidence: 87%

Section: Discussion Of Psd Shapesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Long term variability of Cygnus X-1

Grinberg

Pottschmidt

Böck

et al. 2014

A&A

116

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“…Uttley et al (2002) applied this method to the first 3 years of observations of four AGN. They found evidence for bends, or breaks, in the PSDs in three AGN,NGC 5506,although not in NGC 5548. GBHs are found in a variety of 'states' (eg McClintock and Remillard 2003;Cui et al 1997a), the most common of which are the so called low flux, hard spectrum (or 'low') state, and the high flux, soft spectrum (or 'high') state. In the standard Comptonisation models for the production of X-ray emission, different physical regimes apply to low and high states, with a higher seed photon flux in the high state, leading to a cooler Comptonising corona (eg Zdziarski et al 2002).…”

Section: Introductionmentioning

confidence: 99%

Combined long and short timescale X-ray variability of NGC 4051 with RXTE and XMM-Newton

McHardy¹,

Papadakis²,

Uttley³

et al. 2004

Nuclear Physics B - Proceedings Supplements

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We present a comprehensive examination of the X-ray variability of the narrow line Seyfert 1 (NLS1) galaxy NGC 4051, one of the most variable AGN in the sky. We combine over 6.5 years of frequent monitoring observations by RXTE with a > 100 ks continuous observation by XMM-Newton and so present an overall 2-10 keV powerspectral density (PSD) covering an unprecedent frequency range of over 6.5 decades from < 10 −8 to > 10 −2 Hz. The combined RXTE and XMM-Newton PSD is a very good match to the PSD of the galactic black hole binary system (GBH) Cyg X-1 when in a 'high', rather than 'low', state providing the first definite confirmation of an AGN in a 'high' state. We also find that a bending powerlaw, rather than a sharply broken powerlaw, besides being more physical, is a much better description of the high state PSD of Cyg X-1 and is also a better description of the PSD of NGC 4051.At low frequencies the PSD of NGC 4051 has a slope of -1.1 bending, at a frequency ν B = 8 +4 −3 × 10 −4 Hz, to a slope of α H ∼ −2. Although ν B does not depend on photon energy, α H is steeper at lower energies. If ν B scales with mass, we imply a black hole mass of 3 +2 −1 × 10 5 M ⊙ in NGC 4051, which is consistent with the recently reported reverberation value of 5 +6 −3 × 10 5 M ⊙ . Hence NGC 4051 is emitting at ∼ 30% L Edd . NGC 4051 follows the same rms-flux relationship as GBHs, consistent with higher Fourier frequencies being associated with smaller radii.From the cross-powerspectra and cross-correlation functions between XMMNewton lightcurves in different energy bands, we note that the higher energy photons lag the lower energy ones. We also note that the lag is greater for variations of longer Fourier period and increases with the energy separation of the bands. Variations in different wavebands are very coherent at long Fourier periods but the coherence decreases at shorter periods and as the energy separation between bands increases. This behaviour is again similar to that of GBHs, and of MCG-6-30-15, and suggests a radial distribution of frequencies and photon energies with higher energies and higher frequencies being associated with smaller radii.Combining our observations with observations from the literature we find it is not possible to fit all AGN to the same linear scaling of break timescale with black hole mass. However broad line AGN are consistent with a linear scaling of break timescale with mass from Cyg X-1 in its low state and NLS1 galaxies scale better with Cyg X-1 in its high state. We suggest that the relationship between black hole mass and break timescale is a function of at least one other underlying parameter which may be accretion rate or black hole spin or both.

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“…While an optically thick corona could precess with the accretion disc providing it had some nonuniform geometry, it is generally accepted that the corona is optically thin (e.g. Cui et al 1997). In this case the corona would not precess with the disc unless it was a very thin layer just above and below the disc, and therefore the BATSE modulation should be comparable with that of ASM.…”

Section: Discussionmentioning

confidence: 99%

Orbital, Precessional and Flaring Variability in Cygnus X-1

Brocksopp¹,

Fender²,

Larianov³

et al.

Black Holes in Binaries and Galactic Nuclei: Diagnostics, Demography and Formation

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We present the results of a 2.5-year multiwavelength monitoring programme of Cygnus X-1, making use of hard and soft X-ray data, optical spectroscopy, UBVJHK photometry and radio data. In particular we confirm that the 5.6-day orbital period is apparent in all wavebands and note the existence of a wavelength-dependence to the modulation, in the sense that higher energies reach minimum first. We also find a strong modulation at a period of 142 ± 7 days, which we suggest is due to precession and/or radiative warping of the accretion disc. Strong modulation of the hard and soft X-ray flux at this long period may not be compatible with simple models of an optically thin accretion flow and corona in the low state. We present the basic components required for more detailed future modelling of the system -including a partially optically thick jet, quasi-continuous in the low state, the base of which acts as the Comptonising corona. In addition, we find that there are a number of flares which appear to be correlated in at least two wavebands and generally in more. We choose two of these flares to study in further detail and find that the hard and soft X-rays are well-correlated in the first and that the soft X-rays and radio are correlated in the second. In general, the optical and infrared show similar behaviour to each other but are not correlated with the X-rays or radio.

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Temporal Properties of Cygnus X‐1 during the Spectral Transitions

Cited by 180 publications

References 30 publications

Long term variability of Cygnus X-1

Long term variability of Cygnus X-1

Combined long and short timescale X-ray variability of NGC 4051 with RXTE and XMM-Newton

Orbital, Precessional and Flaring Variability in Cygnus X-1

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