The rms-flux relation in accreting objects: not a simple  “volume control”

Uttley, P.; McHardy, I. M.; Vaughan, S.

doi:10.1051/0004-6361/201630044

Cited by 11 publications

(24 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This makes sense physically where each radius acts as a low pass filter with variations suppressed on a local viscous timescale (e.g. Churazov et al 2001;Ingram et al 2016), although in reality these are well known to be coupled (Uttley et al 2017). Whilst we do not have a-priori knowledge of the nature of the Lorentzians that might describe the shape of the broad band noise in any of our energy-dependent observations, we can test the impact Vaughan 2005).…”

Section: Complex Broad-band Noise Modelsmentioning

confidence: 99%

Searching for energy-resolved quasi-periodic oscillations in AGN

Ashton

Middleton

2021

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

X-ray quasi-periodic oscillations (QPOs) in active galactic nucleus (AGN) allow us to probe and understand the nature of accretion in highly curved space–time, yet the most robust form of detection (i.e. repeat detections over multiple observations) has been limited to a single source to-date, with only tentative claims of single observation detections in several others. The association of those established AGN QPOs with a specific spectral component has motivated us to search the XMM–Newton archive and analyse the energy-resolved light curves of 38 bright AGNs. We apply a conservative false alarm testing routine folding in the uncertainty and covariance of the underlying broad-band noise. We also explore the impact of red-noise leak and the assumption of various different forms (power-law, broken power-law, and Lorentzians) for the underlying broad-band noise. In this initial study, we report QPO candidates in six AGNs (seven including one tentative detection in MRK 766) from our sample of 38, which tend to be found at characteristic energies and, in four cases, at the same frequency across at least two observations, indicating they are highly unlikely to be spurious in nature.

show abstract

Section: Complex Broad-band Noise Modelsmentioning

confidence: 99%

Searching for energy-resolved quasi-periodic oscillations in AGN

Ashton

Middleton

2021

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

show abstract

“…The lognormal distribution: This distribution is frequently used in active galactic nuclei (AGN) and X-ray binaries: The lognormal distribution results from many unresolved subprocesses which are Gaussian and amplify each other into a single observable. Thus the lognormal distribution results from the product of the Gaussian subprocesses (e.g., Uttley et al 2005). This model has been applied to Sgr A* in all past studies of the NIR flux distribution (see, e.g., Dodds-Eden et al 2009;Witzel et al 2012Witzel et al , 2018Hora et al 2014).…”

Section: Analytic Distribution Functionmentioning

confidence: 99%

“…Such a distribution function has been proposed by Dodds-Eden et al (2010) and has been interpreted in the following sense: The quiescent low flux density states are associated with a lognormal distribution. The lognormal flux distribution is motivated in analogy to the flux distribution of many accreting compact objects such as X-ray binaries or AGN (e.g., Uttley et al 2005). On top of the quiescent phase, there exists a secondary process which creates the flux density tail responsible for the highest flux densities, which coincide with the observed flaring events.…”

Section: Composite Distribution Functionsmentioning

confidence: 99%

The flux distribution of Sgr A*

Abuter

Amorim

Bauböck

et al. 2020

A&A

View full text Add to dashboard Cite

The Galactic center black hole Sagittarius A* is a variable near-infrared (NIR) source that exhibits bright flux excursions called flares. When flux from Sgr A* is detected, the light curve has been shown to exhibit red noise characteristics and the distribution of flux densities is non-linear, non-Gaussian, and skewed to higher flux densities. However, the low-flux density turnover of the flux distribution is below the sensitivity of current single-aperture telescopes. For this reason, the median NIR flux has only been inferred indirectly from model fitting, but it has not been directly measured. In order to explore the lowest flux ranges, to measure the median flux density, and to test if the previously proposed flux distributions fit the data, we use the unprecedented resolution of the GRAVITY instrument at the VLTI. We obtain light curves using interferometric model fitting and coherent flux measurements. Our light curves are unconfused, overcoming the confusion limit of previous photometric studies. We analyze the light curves using standard statistical methods and obtain the flux distribution. We find that the flux distribution of Sgr A* turns over at a median flux density of (1.1 ± 0.3) mJy. We measure the percentiles of the flux distribution and use them to constrain the NIR K-band spectral energy distribution. Furthermore, we find that the flux distribution is intrinsically right-skewed to higher flux density in log space. Flux densities below 0.1 mJy are hardly ever observed. In consequence, a single powerlaw or lognormal distribution does not suffice to describe the observed flux distribution in its entirety. However, if one takes into account a power law component at high flux densities, a lognormal distribution can describe the lower end of the observed flux distribution. We confirm the rms–flux relation for Sgr A* and find it to be linear for all flux densities in our observation. We conclude that Sgr A* has two states: the bulk of the emission is generated in a lognormal process with a well-defined median flux density and this quiescent emission is supplemented by sporadic flares that create the observed power law extension of the flux distribution.

show abstract

“…A linear rms-flux relation is a consequence of a lognormal transform of an underlying Gaussian process light curve (Uttley et al 2005, Uttley et al 2017. We test if some other transformation of an underlying Gaussian light curve, g(t), is producing the observed light curves x(t) in IRAS 13224-3809.…”

Section: Rms-flux Relationmentioning

confidence: 99%

The remarkable X-ray variability of IRAS 13224–3809 – I. The variability process

Alston

Fabian

Buisson

et al. 2018

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

We present a detailed X-ray timing analysis of the highly variable NLS1 galaxy, IRAS 13224-3809. The source was recently monitored for 1.5 Ms with XMM-Newton which, combined with 500 ks archival data, makes this the best studied NLS1 galaxy in X-rays to date. We apply standard time-and Fourier-domain techniques in order to understand the underlying variability process. The source flux is not distributed lognormally, as expected for all types of accreting sources. The first non-linear rms-flux relation for any accreting source in any waveband is found, with rms ∝ flux 2/3 . The light curves exhibit significant strong non-stationarity, in addition to that caused by the rms-flux relation, and are fractionally more variable at lower source flux. The power spectrum is estimated down to ∼ 10 −7 Hz and consists of multiple peaked components: a lowfrequency break at ∼ 10 −5 Hz, with slope α < 1 down to low frequencies; an additional component breaking at ∼ 10 −3 Hz. Using the high-frequency break we estimate the black hole mass M BH = [0.5 − 2] × 10 6 M , and mass accretion rate in Eddington units, m Edd ∼ > 1. The broadband PSD and accretion rate make IRAS 13224-3809 a likely analogue of Very-high/Intermediate state black hole X-ray binaries. The non-stationarity is manifest in the PSD with the normalisation of the peaked components increasing with decreasing source flux, as well as the low-frequency peak moving to higher frequencies. We also detect a narrow coherent feature in the soft band PSD at 7×10 −4 Hz, modelled with a Lorentzian the feature has Q ∼ 8 and an rms ∼ 3 %. We discuss the implication of these results for accretion of matter onto black holes.

show abstract

The rms-flux relation in accreting objects: not a simple “volume control”

Cited by 11 publications

References 23 publications

Searching for energy-resolved quasi-periodic oscillations in AGN

Searching for energy-resolved quasi-periodic oscillations in AGN

The flux distribution of Sgr A*

The remarkable X-ray variability of IRAS 13224–3809 – I. The variability process

Contact Info

Product

Resources

About