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Probing the temporal variability of Cygnus X-1 into the soft state
Stockholm University, Faculty of Science, Department of Astronomy.
Stockholm University, Faculty of Science, Department of Astronomy.
Stockholm University, Faculty of Science, Department of Astronomy.
2006 (English)In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 452, no 3, 975-984 p.Article in journal (Refereed) Published
Abstract [en]

Building on results from previous studies of Cygnus X-1, we analyze Rossi X-ray Timing Explorer (RXTE) data taken when the source was in the soft and transitional spectral states. We look at the power spectrum in the 0.01-50 Hz range, using a model consisting of a cut-off power-law and two Lorentzian components. We are able to constrain the relation between the characteristic frequencies of the Lorentzian components, and show that it is consistent with a power-law relation having the same index (1.2) as previously reported for the hard state, but shifted by a factor ˜2. Furthermore, it is shown that the change in the frequency relation seen during the transitions can be explained by invoking a shift of one Lorentzian component to a higher harmonic, and we explore the possible support for this interpretation in the other component parameters. With the improved soft state results we study the evolution of the fractional variance for each temporal component. This approach indicates that the two Lorentzian components are connected to each other, and unrelated to the power-law component in the power spectrum, pointing to at least two separate emission components.

Place, publisher, year, edition, pages
2006. Vol. 452, no 3, 975-984 p.
Keyword [en]
accretion, accretion disks, stars: binaries: close, stars: individual: Cyg X-1, X-rays: binaries
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:su:diva-20141DOI: doi:10.1051/0004-6361:20054397OAI: oai:DiVA.org:su-20141DiVA: diva2:186666
Available from: 2007-02-27 Created: 2007-02-27 Last updated: 2011-01-11Bibliographically approved

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Axelsson, MagnusBorgonovo, LuisLarsson, Stefan
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