What question did this study set out to answer?

To assess whether Fourier phase lags between hard and soft X-rays in black hole candidates reflect intrinsic properties of the soft photon source or the surrounding Compton cloud.

May 1, 1996Monthly Notices of the Royal Astronomical SocietyOpen Access

Phase lags and coherence of X-ray variability in black hole candidates

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Authors

MNMichael A. NowakWashington University in St. Louis BVBrian VaughanTechnological University Dublin

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Implication

Theoretical modeling reveals X-ray phase lags and coherence primarily probe Compton cloud properties rather than soft input sources, indicating limits in tracing inner accretion disks.

Key Points

To assess whether Fourier phase lags between hard and soft X-rays in black hole candidates reflect intrinsic properties of the soft photon source or the surrounding Compton cloud.
Analyzed theoretical Compton cloud models describing the low (hard) state of black hole candidates.
Evaluated Fourier phase lags, diffusion times, and the cross-power spectral density coherence function across photon energies and Fourier frequencies.
Compared model sensitivity against observational limits from instruments such as Ginga, with reference to Cygnus X-1 observations.
Intrinsic phase lags disappear when output photon energy substantially exceeds input photon energy, leaving a time-lag shelf caused by mean diffusion time differences across the cloud.
Instrumental counting noise in prior missions like Ginga likely obscured the predicted time-lag shelf.
The coherence function decreases exponentially at high Fourier frequencies, indicating that variations in cloud size or temperature on scales over 10 seconds drive coherence loss.

Cite This Study

Nowak et al. (1996) studied this question.

synapsesocial.com/papers/6a0248942f52e40b1a9f46d4 https://doi.org/10.1093/mnras/280.1.227

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Implication

Theoretical modeling reveals X-ray phase lags and coherence primarily probe Compton cloud properties rather than soft input sources, indicating limits in tracing inner accretion disks.

Phase lags and coherence of X-ray variability in black hole candidates

Discussion

Member takes

Implication

Key Points

Cite This Study

Phase lags and coherence of X-ray variability in black hole candidates

Discussion

Member takes

Implication

Key Points

Cite This Study

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