Time Domain Analysis of Variability in Cygnus X-1: Constraints on the Emission Models

Maccarone, Thomas J.; Coppi, P.; Poutanen, Juri

doi:10.1086/312778

Cited by 69 publications

(108 citation statements)

References 23 publications

(37 reference statements)

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“…Recent RXTE observations (Maccarone, Coppi, & Poutanen 2000) clearly show asymmetries of the CCFs, which, however, peak within ∼ 1 ms from zero lag (see Fig. 2).…”

Section: Variability In the Time Domain Auto-and Cross-correlation Fumentioning

confidence: 86%

Understanding spectral variability and time lags in accreting black holes

Poutanen

2001

Advances in Space Research

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I review the temporal/spectral data of accreting black hole sources paying most attention to the properties of the temporal variability such as photon energy dependent auto-and cross-correlation functions, average shot profiles and hardness ratios, and the Fourier frequency dependent time/phase lags. These statistics characterize spectral changes at short time scales that are otherwise impossible to study by direct spectral analysis. The data provide strong constraints on the theoretical models for X-ray production in accreting black holes. Models for the spectral variability of the Comptonized component are briefly reviewed. It is also shown that Compton reflection can have significant impact on the observed temporal characteristics.

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“…Recent RXTE observations (Maccarone, Coppi, & Poutanen 2000) clearly show asymmetries of the CCFs, which, however, peak within ∼ 1 ms from zero lag (see Fig. 2).…”

Section: Variability In the Time Domain Auto-and Cross-correlation Fumentioning

confidence: 86%

Understanding spectral variability and time lags in accreting black holes

Poutanen

2001

Advances in Space Research

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“…Similar to Maccarone et al (2000), we computed the autocorrelation function in three energy bands: 20-50 keV of SuperAGILE, 1.5-5 keV given by the sum of the A and B bands of RXTE/ASM and 5-12 keV from the ASM C band. Apart from the peak at zero lag, no other peak is found, indicating that the source emission does not show periodicity in all energy ranges.…”

Section: Alternative Methods Of Timing Analysismentioning

confidence: 99%

A year-long AGILE observation of Cygnus X-1 in hard spectral state

Monte¹,

Feroci²,

Evangelista

et al. 2010

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Context. Cygnus X-1 (Cyg X-1) is a high mass X-ray binary system, known to be a black hole candidate and one of the brightest sources in the X-ray sky, which shows both variability on all timescales and frequent flares. The source spends most of the time in a hard spectral state, dominated by a power-law emission, with occasional transitions to the soft and intermediate states, where a strong blackbody component emerges. Aims. We present the observation of Cyg X-1 in a hard spectral state performed during the AGILE science verification phase and observing cycle 1 in hard X-rays (with SuperAGILE) and gamma rays (with the gamma ray imaging detector) and lasting for about 160 days with a live time of ∼6 Ms. Methods. We investigated the variability of Cyg X-1 in hard X-rays on different timescales, from ∼300 s up to one day, and we applied different tools of timing analysis, such as the autocorrelation function, the first-order structure function, and the LombScargle periodogram, to our data (from SuperAGILE) and to the simultaneous data in soft X-rays (from RXTE/ASM). We concluded our investigation with a search for emission in the energy range above 100 MeV with the maximum likelihood technique. Results. In the hard X-ray band, the flux of Cyg X-1 shows its typical erratic fluctuations on all timescales with variations of about a factor of two that do not significantly affect the shape of the energy spectrum. From the first-order structure function, we find that the X-ray emission of Cyg X-1 is characterized by antipersistence (anticorrelation in the time series, with an increase in the emission likely followed by a decrease), indicative of a negative feedback mechanism at work. In the gamma ray data a statistically significant point-like source at the position of Cyg X-1 is not found, and the upper limit on the flux is 5 × 10 −8 ph cm −2 s −1 over the whole observation (160 days). Finally we compared our upper limit in gamma rays with the expectation of various models of the Cyg X-1 emission, both of hadronic and leptonic origin, in the GeV-TeV band. Conclusions. The time history of Cyg X-1 in the hard X-ray band over 13 months (not continuous) is shown. Different analysis tools do not provide fully converging results of the characteristic timescales in the system, suggesting that the timescales found in the structure function are not intrinsic to the physics of the source. While Cyg X-1 is not detected in gamma rays, our upper limit is a factor of two lower than the EGRET one and is compatible with the extrapolation of the flux measured by COMPTEL in the same spectral state.

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“…With this modification we are able to explain two additional observational facts exhibited by Cygnus X-1. One is the narrowing of the autocorrelation function with increasing photon energy (Maccarone et al 2000) and the other is the hardening of the high-frequency power spectrum with increasing photon energy (Nowak et al 1999). Preliminary results of this work appeared in Kylafis et al (2004).…”

Section: Introductionmentioning

confidence: 68%

“…In the context of our model, this can be understood as the association of the state transitions with a more extended jet. Maccarone et al (2000) computed the autocorrelation functions (ACF) of the light curves of Cygnus X-1 in different energy bands and showed that the width of the ACF decreases with photon energy. This imposes strong constraints on the different models that attempt to describe both the spectral and the temporal properties of accreting black-hole binaries.…”

Section: Energy and Time-lag Spectramentioning

confidence: 99%

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Spectra and time variability of Galactic black-hole X-ray sources in the low/hard state

Kylafis

Giannios

Psaltis³

2004

AIP Conference Proceedings

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Abstract.We propose a jet model for the low/hard state of galactic black-hole X-ray sources which explains a) the X-ray spectra; b) the time-lag spectra; c) the increase of the variability amplitude (QPO and high frequency) with increasing photon energy; and d) the narrowing of the autocorrelation function with increasing photon energy. The model (in its simplest form) assumes that i) there is a uniform magnetic field along the axis of the jet; ii) the electron density in the jet is inversely proportional to distance; and iii) the jet is "hotter" near its center than at its periphery. We have performed Monte Carlo simulations of Compton upscattering of soft photons from the accretion disk and have found power-law high-energy spectra with photon-number index in the range 1.5-2, power-law time lags versus Fourier frequency with index ∼0.8, and an increase of the rms amplitude of variability and a narrowing of the autocorrelation function with photon energy as has been observed in Cygnus X-1. Similar energy spectra and time variability have been observed in neutron-star systems in the island state. It is therefore quite likely that a similar model holds for these sources as well.

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Time Domain Analysis of Variability in Cygnus X-1: Constraints on the Emission Models

Cited by 69 publications

References 23 publications

Understanding spectral variability and time lags in accreting black holes

Understanding spectral variability and time lags in accreting black holes

A year-long AGILE observation of Cygnus X-1 in hard spectral state

Spectra and time variability of Galactic black-hole X-ray sources in the low/hard state

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