Dead-Time Modifications to Fast Fourier Transform Power Spectra

Zhang, W.; Jahoda, K.; Swank, J. H.; Morgan, E.; Giles, A. B.

doi:10.1086/176111

Cited by 247 publications

(225 citation statements)

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“…Then, the average PSDs have been Poisson noise-subtracted, and renormalized adopting the squared fractional rms normalization (Miyamoto et al 1991). We corrected the RXTE data for instrumental dead-time (which produces an over-estimate of the intrinsic Poisson noise level) using the dead-time model of Zhang et al (1995Zhang et al ( , 1996. Since the variability power S/N ratio drops at high frequencies, we limited the analysis to frequencies < ∼ 50 Hz.…”

Section: Discussionmentioning

confidence: 99%

The evolution of the disc variability along the hard state of the black hole transient GX 339-4

Marco¹,

Ponti²,

Muñoz-Darias³

et al. 2015

Mon. Not. R. Astron. Soc.

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We report on the analysis of hard-state power spectral density function (PSD) of GX 339-4 down to the soft X-ray band, where the disc significantly contributes to the total emission. At any luminosity probed, the disc in the hard state is intrinsically more variable than in the soft state. However, the fast decrease of disc variability as a function of luminosity, combined with the increase of disc intensity, causes a net drop of fractional variability at high luminosities and low energies, which reminds the well-known behaviour of disc-dominated energy bands in the soft state. The peak-frequency of the high-frequency Lorentzian (likely corresponding to the high-frequency break seen in active galactic nuclei, AGN) scales with luminosity, but we do not find evidence for a linear scaling. In addition, we observe that this characteristic frequency is energy-dependent. We find that the normalization of the PSD at the peak of the high-frequency Lorentzian decreases with luminosity at all energies, though in the soft band this trend is steeper. Together with the frequency shift, this yields quasi-constant high frequency (5-20 Hz) fractional rms at high energies, with less than 10 percent scatter. This reinforces previous claims suggesting that the high frequency PSD solely scales with BH mass. On the other hand, this constancy breaks down in the soft band (where the scatter increases to ∼ 30 percent). This is a consequence of the additional contribution from the disc component, and resembles the behaviour of optical variability in AGN.

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Section: Discussionmentioning

confidence: 99%

The evolution of the disc variability along the hard state of the black hole transient GX 339-4

Marco¹,

Ponti²,

Muñoz-Darias³

et al. 2015

Mon. Not. R. Astron. Soc.

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“…The dead-time can also be measured by taking a Fourier transform of time series for a bright source, which would give a broad peak close to the inverse of the dead-time in the power spectrum. This can be compared with that expected for a deadtime corrected Poisson level power (Zhang et al 1995). This yields an estimate of dead-time of around 42 µs (Yadav et al 2016b).…”

Section: The Laxpc Detectorsmentioning

confidence: 93%

Calibration of the Large Area X-Ray Proportional Counter (LAXPC) Instrument on board AstroSat

Antia

Yadav

Agrawal

et al. 2017

ApJS

173

120

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We present the calibration and background model for the Large Area X-ray Proportional Counter (LAXPC) detectors on-board AstroSat. LAXPC instrument has three nominally identical detectors to achieve large collecting area. These detectors are independent of each other and in the event analysis mode, they record the arrival time and energy of each photon that is detected. The detectors have a time-resolution of 10 µs and a dead-time of about 42 µs. This makes LAXPC ideal for timing studies. The energy resolution and peak channel to energy mapping were obtained from calibration on ground using radioactive sources coupled with GEANT4 simulations of the detectors. The response matrix was further refined from observations of the Crab after launch. At around 20 keV the energy resolution of detector is 10-15%, while the combined effective area of the 3 detectors is about 6000 cm 2 .

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“…The rise in the power spectrum at low frequencies (< 60 Hz) is due to low frequency variability of the source while the structure at high frequencies is due to the characteristic effect of dead time. The expected dead time corrected Poisson level power for a system which is non-paralyzable is given by Zhang et al (1995) …”

Section: High Frequency Variabilitymentioning

confidence: 99%

Astrosat/Laxpc Reveals the High-Energy Variability of GRS 1915+105 in the Χ Class

Yadav

Misra

Chauhan

et al. 2016

ApJ

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We present the first quick look analysis of data from nine AstroSat's LAXPC observations of GRS 1915+105 during March 2016 when the source had the characteristics of being in Radio-quiet χ class. We find that a simple empirical model of a disk blackbody emission, with Comptonization and a broad Gaussian Iron line can fit the time averaged 3-80 keV spectrum with a systematic uncertainty of 1.5% and a background flux uncertainty of 4%. A simple deadtime-corrected Poisson noise level spectrum matches well with the observed high frequency power spectra till 50 kHz and as expected the data show no significant high frequency (> 20 Hz) features. Energy dependent power spectra reveal a strong low frequency (2 -8 Hz) Quasi-periodic oscillation (LFQPO) and its harmonic along with broad band noise. The QPO frequency changes rapidly with flux (nearly 4 Hz in ∼ 5 hours). With increasing QPO frequency, an excess noise component appears significantly in the high energy regime (> 8 keV). At the QPO frequencies, the time-lag as a function of energy has a non-monotonic behavior such that the lags decrease with energy till about 15-20 keV and then increase for higher energies. These first look results benchmark the performance of LAXPC at high energies and confirms that its data can be used for more sophisticated analysis such as flux or frequency-resolved spectro-timing studies.

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Dead-Time Modifications to Fast Fourier Transform Power Spectra

Cited by 247 publications

References 0 publications

The evolution of the disc variability along the hard state of the black hole transient GX 339-4

The evolution of the disc variability along the hard state of the black hole transient GX 339-4

Calibration of the Large Area X-Ray Proportional Counter (LAXPC) Instrument on board AstroSat

Astrosat/Laxpc Reveals the High-Energy Variability of GRS 1915+105 in the Χ Class

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