X-ray variability of GX 339 - 4 in its very high state

Miyamoto, S.; Kimura, Kazuhiro; Kitamoto, Shunji; Dotani, Tadayasu; Ebisawa, Ken

doi:10.1086/170837

Cited by 405 publications

(429 citation statements)

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“…The level of variability power due to Poisson noise was determined fitting the high-frequency part (above 100 Hz) of the PSD with a constant. 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.…”

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 PDS of the individual segments were merged together, sorted in order of increasing frequency, and rebinned in frequency to have at least 40 points per bin. The PDS were white noise subtracted and normalized such that their integral over a frequency range ν 1 − ν 2 gives the squared fractional rms variability of the light curves due to variations on time scales from ν −1 2 to ν −1 1 (Belloni & Hasinger 1990;Miyamoto et al 1991). Figure 1 shows the power density spectra (PDS) of all the sources studied in this work, together with the best-fit powerlaw model and residuals.…”

Section: Discussionmentioning

confidence: 99%

Aperiodic variability of low-mass X-ray binaries at very low frequencies

Reig

Papadakis

Kylafis

2003

A&A

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Abstract. We have obtained discrete Fourier power spectra of a sample of persistent low-mass neutron-star X-ray binaries using long-term light curves from the All Sky Monitor on board the Rossi X-ray Timing Explorer. Our aim is to investigate their aperiodic variability at frequencies in the range 1 × 10 −7 −5 × 10 −6 Hz and compare their properties with those of the black-hole source Cyg X-1. We find that the classification scheme that divides LMXBs into Z and atoll sources blurs at very low frequencies. Based on the long-term (∼years) pattern of variability and the results of power-law fits (P(ν) ∝ ν −α ) to the 1 × 10 −7 −5 × 10 −6 Hz power density spectra, low-mass neutron-star binaries fall into three categories. Type I includes all Z sources, except Cyg X-2, and the atoll sources GX9+1 and GX13+1. They show relatively flat power spectra (α < ∼ 0.9) and low variability (rms < ∼ 20%). Type II systems comprise 4U 1636-53, 4U 1735-44 and GX3+1. They are more variable (20% < ∼ rms < ∼ 30%) and display steeper power spectra (0.9 < ∼ α < ∼ 1.2) than type I sources. Type III systems are the most variable (rms > 30%) and exhibit the steepest power spectra (α > 1.2). The sources 4U 1705-44, GX354-0 and 4U 1820-30 belong to this group. GX9+9 and Cyg X-2 appear as intermediate systems in between type I and II and type II and III sources, respectively. We speculate that the differences in these systems may be caused by the presence of different types of mass-donor companions. Other factors, like the size of the accretion disc and/or the presence of weak magnetic fields, are also expected to affect their low-frequency X-ray aperiodic varibility.

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“…The average PDS was obtained by calculating and averaging the power spectra for each interval using Xronos version 5.21. The PDS were normalized according to Miyamoto et al (1991). Figure 2a shows the PDS in the (0.2−10) keV energy band and shows a QPO peak around at ∼ 0.5 mHz (2.4 σ) with an integrated rms of 5% ± 1%.…”

Section: Timing Analysismentioning

confidence: 99%

A search for periodicities from a ULX in the LINER galaxy NGC 4736

Avdan

Akyüz

et al. 2014

Astrophys Space Sci

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We report our findings on a new quasi-periodic oscillation (QPO) and a long period from the ultraluminous X-ray source (ULX) X-2 in nearby galaxy NGC 4736 based on the Chandra and XMM-Newton archival data. To examine the timing properties, power density spectra of the source have been obtained using Fast Fourier Transform. Also the spectral parameters of the source have been calculated by obtaining and fitting the energy spectra. Power density spectrum of this source reveals a QPO peak at 0.73 +0.16 −0.14 mHz with an fractional rms variability of 16% using the Chandra data (in the year 2000-lower state of the source). The XMM-Newton data analysis indicates a peak at 0.53 +0.09 −0.35 mHz with a fractional rms variation of 5% (in the year 2006-higher state of the source). These recovered QPOs overlap within errors and may be the same oscillation. In addition, we detect a long periodicity or a QPO in the Chandra data of about (5.2 ± 2.0) × 10 −5 Hz (∼ 5.4 hrs) over 3 σ confidence level. If this is a QPO, it is the lowest QPO detected from a ULX. The mass of the compact object in ULX X-2 is estimated using the Eddington luminosity and a disk blackbody model in the range (10−80) M ⊙ .

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X-ray variability of GX 339 - 4 in its very high state

Cited by 405 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

Aperiodic variability of low-mass X-ray binaries at very low frequencies

A search for periodicities from a ULX in the LINER galaxy NGC 4736

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