Characterising Anomalous Transport in Accretion Disks from X-ray Observations

Abstract

Abstract. Whilst direct observations of internal transport in accretion disksare not yet possible, measurement of the energy emitted from accreting astrophysical systems can provide useful information on the physical mechanisms at work. Here we examine the unbroken multi-year time variation of the total X-ray flux from three sources: Cygnus X-1, the microquasar GRS1915+105, and for comparison the nonaccreting Crab nebula. To complement previous analyses, we demonstrate that the application of advanced statistical methods to these observational time-series reveals important contrasts in the nature and scaling properties of the transport processes operating within these sources. We find the Crab signal resembles Gaussian noise; the Cygnus X-1 signal is a leptokurtic random walk whose self-similar properties persist on timescales up to three years; and the GRS1915+105 signal is similar to that from Cygnus X-1, but with self-similarity extending possibly to only a few days. This evidence of self-similarity provides a robust quantitative characterisation of anomalous transport occuring within the systems.

Recurrence plot statistics and the effect of embedding

“…Comparisons between repeated patterns in signals from nonlinear systems are particularly valuable when the systems in question are spatially extended and evolve in a nonstationary fashion. Macroscopic plasmas, whether naturally occuring or created in fusion experiments, often fall into this category, which presents a substantial challenge to the techniques of statistical and time series analysis; see, for example, the discussions in recent studies of astrophysical [29], solar [30], and fusion [31] plasma observations. The successful application of recurrence plots and the concepts of information theory to the geomagnetic plasma timeseries studied in the present paper is, therefore, encouraging.…”

Polarized NIR and X-ray flares from Sagittarius A*

“…flaring, and a low flux density state. Greenhough et al (2001) outline the importance of scaling properties of the transport processes operating within accretion disks. Pessah et al (2007) present a scaling law between magnetic stress in units of the gas pressure and the vertical disk cell size in units of the pressure scale height implying that the magnetic field and source component size follow a power law relation.…”