Publication date: Jun 2008
Abstract:
A long discussion has been devoted to the issue of clustering of the kHz
quasi periodic oscillation (QPO) frequency ratios in the neutron star
sources. While the distribution of ratios inferred from an occurrence of
a single QPO seems to be consistent with a random walk, the distribution
based on simultaneous detections of both peaks indicates a preference of
ratios of small integers. Based on the public RXTE data we further
investigate this issue for the source 4U1636-53. Quality factors and rms
amplitudes of both the QPOs nearly equal at the points where the
frequencies are commensurable, and where the twin QPO detections
cluster. We discuss a connection of the clustering with the varying
properties of the two QPO modes. Assuming approximate relations for the
observed correlations of the QPO properties, we attempt to reproduce the
frequency and ratio distributions using a simple model of a random-walk
evolution along the observed frequency-frequency correlation. We obtain
results which are in qualitative agreement with the observed
distributions.
Authors:
Török, G.; Abramowicz, M. A.; Bakala, P.; Bursa, M.; Horák, J.; Rebusco, P.; Stuchlik, Z.;