<i>CHANDRA</i>X-RAY SPECTROSCOPY OF THE FOCUSED WIND IN THE CYGNUS X-1 SYSTEM. I. THE NONDIP SPECTRUM IN THE LOW/HARD STATE

Hanke, Manfred; Wilms, J.; Nowak, Michael A.; Pottschmidt, K.; Schulz, Norbert S.; Lee, Julia C.

doi:10.1088/0004-637x/690/1/330

Cited by 95 publications

(136 citation statements)

References 79 publications

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“…For example, Feng & Cui (2002) discuss a long dip of at least ∼3 ks that shows complex substructure. Prolonged periods of increased absorption are also clearly seen in the long uninterrupted observations possible with Chandra (Hanke et al 2008). Given these previous measurements and the size of our sample, the detection of several strong absorption events as discussed in Sect.…”

Section: Discussion and Comparison To Earlier Resultssupporting

confidence: 64%

“…Boroson & Vrtilek (2010) classified 102 of these observations as hard states and used them to demonstrate the orbital variability of absorption in the hard state, but did not have enough data taken during softer states. At the same time, higher sensitivity snapshots at different φ orb with Chandra (Miller et al 2005;Hanke et al 2009;Miškovičová et al 2015) and Suzaku Miller et al 2012;Yamada et al 2013) revealed a complex structure of the wind with highly Grinberg et al (2013).…”

Section: Introductionmentioning

confidence: 92%

“…As HDE 226868 fills > ∼ 90% of its Roche lobe (Gies et al 2003) and has a strong (a few 10 −6 M yr −1 , Gies et al 2003) fast wind, the black hole accretes via a focussed wind (Friend & Castor 1982;Gies & Bolton 1986a,b;Sowers et al 1998;Miller et al 2005;Hanke et al 2009;Hell et al 2013;Miškovičová et al 2015, and others). Values for ∞ for HDE 226868 vary in the literature: Davis & Hartmann (1983) obtain (2300±400) km s −1 in the hard state, but Vrtilek et al (2008) find 1420 km s −1 in the soft state.…”

Section: Introductionmentioning

confidence: 96%

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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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Section: Discussion and Comparison To Earlier Resultssupporting

confidence: 64%

Section: Introductionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 96%

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Long term variability of Cygnus X-1

Grinberg

Leutenegger

Hell

et al. 2015

A&A

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“…Some disagreement between the MEG and HEG spectrum in the 3-5 keV energy range is an indication of pileup (discussed in more detail in Section 2.2), because light is dispersed over smaller angles with the MEG as compared to the HEG. To test for possible non-linear effects in the HEG arms, we applied the pileup correction simple gpile2 (Nowak et al 2008;Hanke et al 2009) with the physical spectral models described below. We found that the MEG and HEG arms could be fit simultaneously with less than 1% of HEG counts being affected by pileup.…”

Section: Fit To the Hetg Spectrummentioning

confidence: 99%

The dust scattering halo of Cygnus X-3

Corrales

Paerels

2015

Mon. Not. R. Astron. Soc.

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Dust grains scatter X-ray light through small angles, producing a diffuse halo image around bright X-ray point sources situated behind a large amount of interstellar material. We present analytic solutions to the integral for the dust scattering intensity, which allow for a Bayesian analysis of the scattering halo around Cygnus X-3. Fitting the optically thin 4-6 keV halo surface brightness profile yields the dust grain size and spatial distribution. We assume a power law distribution of grain sizes (n ∝ a −p ) and fit for p, the grain radius cut-off a max , and dust mass column. We find that a p ≈ 3.5 dust grain size distribution with a max ≈ 0.2 µm fits the halo profile relatively well, whether the dust is distributed uniformly along the line of sight or in clumps. We find that a model consisting of two dust screens, representative of foreground spiral arms, requires the foreground Perseus arm to contain 80% of the total dust mass. The remaining 20% of the dust, which may be associated with the outer spiral arm of the Milky Way, is located within 1 kpc of Cyg X-3. Regardless of which model was used, we found τ sca ∼ 2 E −2 keV . We examine the energy resolved halos of Cyg X-3 from 1 -6 keV and find that there is a sharp drop in scattering halo intensity when E < 2 − 3 keV, which cannot be explained with multiple scattering effects. We hypothesize that this may be caused by large dust grains or material with unique dielectric properties, causing the scattering cross-section to depart from the Rayleigh-Gans approximation that is used most often in X-ray scattering studies. The foreground Cyg OB2 association, which contains several evolved stars with large extinction values, is a likely culprit for grains of unique size or composition.

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“…Because of its brightness and persistent emission, Cyg X-1 is one of the best studied BHs. In addition to studies of snapshot observations (e.g., Gierliński et al 1999;Di Salvo et al 2001;Frontera et al 2001;Makishima et al 2008;Hanke et al 2009), most recent work has concentrated on the long-term behavior of the source from a monitoring campaign with the Rossi X-Ray Timing Explorer (RXTE) at a two week sampling that started in 1998 and is still ongoing (Pottschmidt et al 2003;Gleissner et al 2004a,b;Axelsson et al 2005;Wilms et al 2006, and references therein). The motivation of the present work was to fill the gap between the biweekly time scale and individual RXTE pointings with an intensive quasi-continuous observation spanning 10 days.…”

Section: Introductionmentioning

confidence: 99%

Spectro-timing analysis of Cygnus X-1 during a fast state transition

Böck

Grinberg

Pottschmidt

et al. 2011

A&A

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We present the analysis of two long, quasi-uninterrupted RXTE observations of Cygnus X-1 that span several days within a 10 d interval. The spectral characteristics during this observation cover the region where previous observations have shown the source to be most dynamic. Despite that the source behavior on time scales of hours and days is remarkably similar to that on year time scales. This includes a variety of spectral/temporal correlations that previously had only been observed over Cyg X-1's long-term evolution. Furthermore, we observe a full transition from a hard to a soft spectral state that occurs within less than 2.5 h -shorter than previously reported for any other similar Cyg X-1 transition. We describe the spectra with a phenomenological model dominated by a broken power law, and we fit the X-ray variability power spectra with a combination of a cutoff power law and Lorentzian components. The spectral and timing properties are correlated: the power spectrum Lorentzian components have an energy-dependent amplitude, and their peak frequencies increase with photon spectral index. Averaged over 3.2−10 Hz, the time lag between the variability in the 4.5−5.7 keV and 9.5−15 keV bands increases with decreasing hardness when the variability is dominated by the Lorentzian components during the hard state. The lag is small when there is a large power law noise contribution, shortly after the transition to the soft state. Interestingly, the soft state not only shows the shortest lags, but also the longest lags when the spectrum is at its softest and faintest. We discuss our results in terms of emission models for black hole binaries.

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CHANDRAX-RAY SPECTROSCOPY OF THE FOCUSED WIND IN THE CYGNUS X-1 SYSTEM. I. THE NONDIP SPECTRUM IN THE LOW/HARD STATE

Cited by 95 publications

References 79 publications

Long term variability of Cygnus X-1

Long term variability of Cygnus X-1

The dust scattering halo of Cygnus X-3

Spectro-timing analysis of Cygnus X-1 during a fast state transition

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