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Tracking the inner edge of the accretion disc in Cygnus X-1
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, Department of Astronomy.
2008 (English)In: 37th COSPAR Scientific Assembly, 2008, E15-0020 p.Conference paper, Published paper (Other academic)
Abstract [en]

Analyzing the archival data from the Rossi X-Ray Timing Explorer, we have studied the power density spectra (PDS) of Cygnus X-1 from 1996 to 2003. Applying a model with few components we show good fits to the PDS between 0.01 Hz and 25 Hz, and are able to track their evolution through all spectral states of the source. We confirm the relation between characteristic frequencies previously seen in both neutron star and black-hole candidate systems, and show the changes in this relation during transitional and soft states of the source. Applying a model of relativistic precession to explain the frequency relation shows remarkable agreement with the hard state data, but cannot explain the behavior in the soft state without additional assumptions. This identification makes the PDS a sensitive probe of the inner radius of the accretion disc. Analyzing the components of the PDS we find evidence of at least two separate emission components. At longer ( 1 hour) timescales, we study Cygnus X-1 during periods of low flux in the hard state, and find changes in the hardness-flux correlation. We interpret our results as signs of the accretion disc being truncated far from the innermost stable orbit, with an inner disc radius greater than 50 gravitational radii, in agreement with our results from the PDS. Our findings are compared to estimates of the viscous timescale responsible for small scale variability in the system.

Place, publisher, year, edition, pages
2008. E15-0020 p.
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:su:diva-18297OAI: oai:DiVA.org:su-18297DiVA: diva2:184820
Available from: 2009-01-25 Created: 2009-01-25Bibliographically approved

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