Monitoring Cygnus X-1 with RXTE

Wilms, J.; Pottschmidt, K.; Nowak, Michael A.; Gleissner, T.; Pooley, G. G.; Remillard, Ronald A.; Staubert, R.; Heindl, W. A.; Uttley, P.; Fender, R. P.

doi:10.1016/j.nuclphysbps.2004.04.076

Cited by 3 publications

(4 citation statements)

References 8 publications

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“…Energy dependence of the temporal behavior can be studied by computing the PDS in 3 or 4 broad energy bins as has been reported for RXTE data (Wilms et al 2004). The complete event mode data of LAXPC allows for the fractional rms to be integrated over a certain frequency range with finer energy bins.…”

Section: Timing Analysismentioning

confidence: 99%

A stochastic propagation model to the energy dependent rapid temporal behaviour of Cygnus X-1 as observed by AstroSat in the hard state

Maqbool

Mudambi

Misra

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We report the results from analysis of six observations of Cygnus X-1 by Large Area X-ray Proportional Counters (LAXPC) and Soft X-ray Telescope (SXT) on-board AstroSat, when the source was in the hard spectral state as revealed by the broad band spectra. The spectra obtained from all the observations can be described by a single temperature Comptonizing region with disk and reflection components. The event mode data from LAXPC provides unprecedented energy dependent fractional root mean square (rms) and time-lag at different frequencies which we fit with empirical functions. We invoke a fluctuation propagation model for a simple geometry of a truncated disk with a hot inner region. Unlike other propagation models, the hard X-ray emission (> 4 keV) is assumed to be from the hot inner disk by a single temperature thermal Comptonization process. The fluctuations first cause a variation in the temperature of the truncated disk and then the temperature of the inner disk after a frequency dependent time delay. We find that the model can explain the energy dependent rms and time-lag at different frequencies.

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Section: Timing Analysismentioning

confidence: 99%

A stochastic propagation model to the energy dependent rapid temporal behaviour of Cygnus X-1 as observed by AstroSat in the hard state

Maqbool

Mudambi

Misra

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…Since then a large number of analysis has been undertaken on several RXTE data sets of Cygnus X-1 and now results of comprehensive timing analysis using nearly all RXTE observations of the source are available (e.g. Wilms et al 2004).…”

Section: Introductionmentioning

confidence: 99%

“…RXTE analysis have shown that for the hard state the variability of Cygnus X-1 is primarily between ∼ 0.1 and ∼ 10 Hz and its power spectrum can be approximately described by two to four broad lorentzians in this frequency range (e.g. Nowak et al 1999;Wilms et al 2004). Time lag of high energy photons with respect to the low energy ones are known to approximately increase linearly with logarithm of the energy.…”

mentioning

confidence: 99%

AstroSat/LAXPC Observation of Cygnus X-1 in the Hard State

Misra¹,

Yadav²,

Chauhan³

et al. 2017

ApJ

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We report the first analysis of data from AstroSat/LAXPC observations of Cygnus X-1 in January 2016. LAXPC spectra reveals that the source was in the canonical hard state, represented by a prominent thermal Comptonization component having a photon index of ∼ 1.8 and high temperature kT e > 60 keV along with weak reflection and possible disk emission. The power spectrum can be characterized by two broad lorentzian functions centered at ∼ 0.4 and ∼ 3 Hz. The r.m.s of the low frequency component decreases from ∼ 15% at around 4 keV to ∼ 10% at around 50 keV, while that of the high frequency one varies less rapidly from ∼ 13.5% to ∼ 11.5% in the same energy range. The time lag between the hard (20-40 keV) and soft (5-10 keV) bands varies in a step-like manner being nearly constant at ∼ 50 milli-seconds from 0.3 to 0.9 Hz, decreasing to ∼ 8 milli-seconds from 2 to 5 Hz and finally dropping to ∼ 2 milli-seconds for higher frequencies. The time lags increase with energy for both the low and high frequency components. The event mode LAXPC data allows for flux resolved spectral analysis on a time-scale of 1 second, which clearly shows that the photon index increased from ∼ 1.72 to ∼ 1.80 as the flux increased by nearly a factor of two. We discuss the results in the framework of the fluctuation propagation model.

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“…Another critical aspect of the temporal behaviour of black hole X-ray binaries is that typically, the systems show hard lags such that the high energy photons are delayed relative to the soft ones. The time-lags increase logarithmically with energy and are surprisingly frequency dependent, t lag ∝ f −0.7 (Miyamoto et al, 1988;Nowak et al, 1999;Wilms et. al., 2004).…”

Section: Introductionmentioning

confidence: 98%

Modeling the response of a standard accretion disc to stochastic viscous fluctuations

Ahmad,

Misra,

Iqbal

et al. 2017

Preprint

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The observed variability of X-ray binaries over a wide range of time-scales can be understood in the framework of a stochastic propagation model, where viscous fluctuations at different radii induce accretion rate variability that propagate inwards to the X-ray producing region. The scenario successfully explains the power spectra, the linear rms-flux relation as well as the time-lag between different energy photons. The predictions of this model have been obtained using approximate analytical solutions or empirically motivated models which take into account the effect of these propagating variability on the radiative process of complex accretion flows. Here, we study the variation of the accretion rate due to such viscous fluctuations using a hydro-dynamical code for the standard geometrically thin, gas pressure dominated α-disc with a zero torque boundary condition. Our results confirm earlier findings that the time-lag between a perturbation and the resultant inner accretion rate variation depends on the frequency (or time-period) of the perturbation. Here we have quantified that the time-lag t lag ∝ f −0.54 , for time-periods less than the viscous time-scale of the perturbation radius and is nearly constant otherwise. This, coupled with radiative process would produce the observed frequency dependent time-lag between different energy bands. We also confirm that if there are random Gaussian fluctuations of the α-parameter at different radii, the resultant inner accretion rate has a power spectrum which is a power-law.

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Monitoring Cygnus X-1 with RXTE

Cited by 3 publications

References 8 publications

A stochastic propagation model to the energy dependent rapid temporal behaviour of Cygnus X-1 as observed by AstroSat in the hard state

A stochastic propagation model to the energy dependent rapid temporal behaviour of Cygnus X-1 as observed by AstroSat in the hard state

AstroSat/LAXPC Observation of Cygnus X-1 in the Hard State

Modeling the response of a standard accretion disc to stochastic viscous fluctuations

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