Volume 519, September 2010
|Number of page(s)||9|
|Section||Stellar structure and evolution|
|Published online||14 September 2010|
Wavelet and R/S analysis of the X-ray flickering of cataclysmic variables*
ICFO - Institut de Ciències Fotòniques, avinguda del Canal Olimpic s/n,
08860 Castelldefels (Barcelona), Spain e-mail: email@example.com
2 Dipartimento di Astronomia, Università di Padova, vicolo dell'Osservatorio 3, 35122 Padova, Italy e-mail: [fabrizio.tamburini;antonio.bianchini]@unipd.it
3 INAF - Osservatorio Astronomico di Capodimonte, salita Moiariello 16, 80131 Napoli, Italy e-mail: firstname.lastname@example.org
Accepted: 31 May 2010
Context. Recently, wavelets and R/S analysis have been used as statistical tools to characterize the optical flickering of cataclysmic variables.
Aims. Here we present the first comprehensive study of the statistical properties of X-ray flickering of cataclysmic variables in order to link them with physical parameters.
Methods. We analyzed a sample of 97 X-ray light curves of 75 objects of all classes observed with the XMM-Newton space telescope. By using the wavelets analysis, each light curve has been characterized by two parameters, α and Σ, that describe the energy distribution of flickering on different timescales and the strength at a given timescale, respectively. We also used the R/S analysis to determine the Hurst exponent of each light curve and define their degree of stochastic memory in time.
Results. The X-ray flickering is typically composed of long time scale events (1.5 α 3), with very similar strengths in all the subtypes of cataclysmic variables (-3 Σ -1.5). The X-ray data are distributed in a much smaller area of the α - Σ parameter space with respect to those obtained with optical light curves. The tendency of the optical flickering in magnetic systems to show higher Σ values than the non-magnetic systems is not encountered in the X-rays. The Hurst exponents estimated for all light curves of the sample are larger than those found in the visible, with a peak at 0.82. In particular, we do not obtain values lower than 0.5. The X-ray flickering presents a persistent memory in time, which seems to be stronger in objects containing magnetic white dwarf primaries.
Conclusions. The similarity of the X-ray flickering in objects of different classes together with the predominance of a persistent stochastic behavior can be explained in terms of magnetically-driven accretion processes acting in a considerable fraction of the analyzed objects.
Key words: novae, cataclysmic variables / X-rays: binaries / accretion, accretion disks / magnetic fields / methods: data analysis
Table 1 is only available in electronic form at http://www.aanda.org
© ESO, 2010
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.