Long term variability of Cygnus X–1

Pottschmidt, K.; Wilms, J.; Nowak, Michael A.; Pooley, G. G.; Gleissner, T.; Heindl, W. A.; Smith, D. M.; Remillard, Ronald A.; Staubert, R.

doi:10.1051/0004-6361:20030906

Cited by 252 publications

(435 citation statements)

References 71 publications

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“…In the HSS, the orbital period is not clearly seen in any energy band. Figure 5 shows our 4-10 keV NPSDs in both states, in comparison with previous works by Cui et al (1997), Pottschmidt et al (2003), and Reig et al (2002). In both states, our results at 10 −4 Hz locate on simple extrapolations of the NPSDs obtained previously by the RXTE/PCA in the frequency region above 10 −3 Hz.…”

Section: Results (2): Using Shorter Data Lengthssupporting

confidence: 85%

“…Pottschmidt et al (2003), the dotted line is that in the HSS in 2-13 keV by Cui et al (1997), and the dot-dashed line is that by Reig et al (2002) where the most data are in the LHS.…”

Section: Energy Spectramentioning

confidence: 93%

“…Above 10 −1 Hz, the index returns to about −1. There is a break again at around 1 Hz, above which the index becomes steeper (e.g., Belloni & Hasinger 1990;Nowak 2000;Negoro et al 2001;Pottschmidt et al 2003). These time scales are thought to reflect the dynamics of accretion flows, and the process of energy dissipation or particle acceleration in a vicinity of the BH.…”

Section: Introductionmentioning

confidence: 99%

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MAXI observations of long-term variations of Cygnus X-1 in the low/hard and the high/soft states

Sugimoto¹,

Mihara²,

Kitamoto³

et al. 2016

Publications of the Astronomical Society of Japan

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Long-term X-ray variability of the black hole binary, Cygnus X-1, was studied with five years of MAXI data from 2009 to 2014, which include substantial periods of the high/soft state, as well as the low/hard state. In each state, Normalized Power Spectrum densities (NPSDs) were calculated in three energy bands of 2-4 keV, 4-10 keV and 10-20 keV. The NPSDs in a frequency from 10 −7 Hz to 10 −4 Hz are all approximated by a power-law function with an index −1.35 ∼ −1.29. The fractional RMS variation η, calculated in the above frequency range, was found to show the following three properties; (1) η slightly decreases with energy in the low/hard state; (2) η increases towards higher energies in the high/soft state; and (3) in the 10-20 keV band, η is 3 times higher in the high/soft state than in the low/hard state. These properties were confirmed through studies of intensity-correlated changes of the MAXI spectra. Of these three findings, the first one is consistent with that seen in the short-term variability during the LHS. The latter two can be understood as a result of high variability of the hard-tail component seen in the high/soft state with the above very low frequency range, although the origin of the variability remains inconclusive.

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Section: Results (2): Using Shorter Data Lengthssupporting

confidence: 85%

“…Pottschmidt et al (2003), the dotted line is that in the HSS in 2-13 keV by Cui et al (1997), and the dot-dashed line is that by Reig et al (2002) where the most data are in the LHS.…”

Section: Energy Spectramentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

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MAXI observations of long-term variations of Cygnus X-1 in the low/hard and the high/soft states

Sugimoto¹,

Mihara²,

Kitamoto³

et al. 2016

Publications of the Astronomical Society of Japan

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“…The intrinsic variability of Cyg X-1 on timescales of hours (Böck et al 2011) to years (Pottschmidt et al 2003;Wilms et al 2006;Shaposhnikov & Titarchuk 2006;Axelsson et al 2006;Grinberg et al 2013) can be classified in terms of X-ray spectral states that also show distinct timing characteristics on timescales below 1 s and are similar for most black hole binaries (for a review see, e.g., Belloni 2010). In particular, the hard state spectrum above ∼2 keV is dominated by a power law component with photon index Γ ∼ 1.7, while in the soft state the thermal emission from the accretion disk is prominent and the contribution from a steeper power law component is low.…”

Section: Introductionmentioning

confidence: 99%

Long term variability of Cygnus X-1

Grinberg

Leutenegger

Hell

et al. 2015

A&A

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Binary systems with an accreting compact object offer a unique opportunity to investigate the strong, clumpy, line-driven winds of early-type supergiants by using the compact object's X-rays to probe the wind structure. We analyze the two-component wind of HDE 226868, the O9.7Iab giant companion of the black hole Cyg X-1, using 4.77 Ms Rossi X-ray Timing Explorer (RXTE) observations of the system taken over the course of 16 years. Absorption changes strongly over the 5.6 d binary orbit, but also shows a large scatter at a given orbital phase, especially at superior conjunction. The orbital variability is most prominent when the black hole is in the hard X-ray state. Our data are poorer for the intermediate and soft state, but show signs for orbital variability of the absorption column in the intermediate state. We quantitatively compare the data in the hard state to a toy model of a focussed Castor-AbbottKlein wind: as it does not incorporate clumping, the model does not describe the observations well. A qualitative comparison to a simplified simulation of clumpy winds with spherical clumps shows good agreement in the distribution of the equivalent hydrogen column density for models with a porosity length on the order of the stellar radius at inferior conjunction; we conjecture that the deviations between data and model at superior conjunction could either be due to lack of a focussed wind component in the model or to a more complicated clump structure.

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“…Belloni et al 2011). The characteristic frequencies move in unison ; notice that in Cyg X-1, a persistent system, one additional component was seen to remain at the same frequency across LHS-HIMS transitions, Pottschmidt et al 2003). Therefore the system displays effectively one frequency.…”

Section: Hard Intermediate Statementioning

confidence: 94%

Accretion and Ejection in Black-Hole X-Ray Transients

Kylafis

Belloni

2014

The Formation and Disruption of Black Hole Jets

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Context. A rich phenomenology has been accumulated over the years regarding accretion and ejection in black-hole X-ray transients (BHTs) and it needs an interpretation. Aims. Here we summarize the current observational picture of the outbursts of BHTs, based on the evolution traced in a hardness -luminosity diagram (HLD), and we offer a physical interpretation. Methods. The basic ingredient in our interpretation is the Poynting -Robertson Cosmic Battery (PRCB, Contopoulos & Kazanas 1998), which provides locally the poloidal magnetic field needed for the ejection of the jet. In addition, we make two assumptions, easily justifiable. The first is that the mass-accretion rate to the black hole in a BHT outburst has a generic bell-shaped form, whose characteristic time scale is much longer than the dynamical or the cooling ones. This is guaranteed by the observational fact that all BHTs start their outburst and end it at the quiescent state, i.e., at very low accretion rate, and that state transitions take place over long time scales (hours to days). The second assumption is that at low accretion rates the accretion flow is geometrically thick, ADAF-like, while at high accretion rates it is geometrically thin. Last, but not least, we demonstrate that the previous history of the system is absolutely necessary for the interpretation of the HLD. Results. Both, at the beginning and the end of an outburst, the PRCB establishes a strong poloidal magnetic field in the ADAF-like part of the accretion flow, and this explains naturally why a jet is always present in the right part of the HLD. In the left part of the HLD, the accretion flow is in the form of a thin disk, and such a disk cannot sustain a strong poloidal magnetic filed. Thus, no jet is expected in this part of the HLD. Finally, the counterclockwise traversal of the HLD is explained as follows: all outbursts start from the quiescent state, in which the inner part of the accretion flow is ADAF-like, threaded by a poloidal magnetic field. As the accretion rate increases and the source moves to the hard state, the poloidal magnetic field in the ADAF forces the flow to remain ADAF and the source to move upwards in the HLD rather than to turn left. Thus, the history of the system determines the counterclockwise traversal of the HLD. As a result, no BHT is expected to ever traverse the entire HLD curve in the clockwise direction. Conclusions. We offer a physical interpretation of accretion and ejection in BHTs with only one parameter, the mass transfer rate, plus the history of the system.

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Long term variability of Cygnus X–1

Cited by 252 publications

References 71 publications

MAXI observations of long-term variations of Cygnus X-1 in the low/hard and the high/soft states

MAXI observations of long-term variations of Cygnus X-1 in the low/hard and the high/soft states

Long term variability of Cygnus X-1

Accretion and Ejection in Black-Hole X-Ray Transients

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