EDP Sciences
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Volume 385, Number 2, April II 2002
Page(s) 693 - 700
Section Physical and chemical processes
DOI http://dx.doi.org/10.1051/0004-6361:20020013

A&A 385, 693-700 (2002)
DOI: 10.1051/0004-6361:20020013

Characterising anomalous transport in accretion disks from X-ray observations

J. Greenhough1, S. C. Chapman1, S. Chaty2, R. O. Dendy3, 1 and G. Rowlands1

1  Department of Physics, University of Warwick, Coventry CV4 7AL, UK
    e-mail: greenh, sandrac@astro.warwick.ac.uk; g.rowlands@warwick.ac.uk
2  Department of Physics & Astronomy, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
    e-mail: S.Chaty@open.ac.uk
3  Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxfordshire OX14 3DB, UK
    e-mail: richard.dendy@ukaea.org.uk

(Received 4 July 2001 / Accepted 2 January 2002)

Whilst direct observations of internal transport in accretion disks are 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 GRS 1915+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 GRS 1915+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.

Key words: accretion, accretion disks -- methods: statistical -- X-rays: general

Offprint request: J. Greenhough, greenh@astro.warwick.ac.uk

SIMBAD Objects in preparation

© ESO 2002