Issue |
A&A
Volume 452, Number 3, June IV 2006
|
|
---|---|---|
Page(s) | 975 - 984 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20054397 | |
Published online | 06 June 2006 |
Probing the temporal variability of Cygnus X-1 into the soft state
Stockholm Observatory, AlbaNova, 106 91 Stockholm, Sweden e-mail: [magnusa;luis]@astro.su.se
Received:
21
October
2005
Accepted:
9
March
2006
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 . 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.
Key words: accretion, accretion disks / stars: binaries: close / stars: individual: Cyg X-1 / X-rays: binaries
© ESO, 2006
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