The puzzling harmonic behavior of the Cathedral QPO in XTE J1859+226

Abstract

Abridged: We present a spectral and temporal analysis of the Cathedral QPO detected in the power density spectra of the microquasar XTE J1859+226 obtained with RXTE. This type of QPO manifests as two peaks with similar amplitudes and harmonically related centroid frequencies (~3 and ~6 Hz). The amplitude of the ~3 Hz feature varies in anticorrelation with the count rate, by about ~50. The ~6 Hz feature shows a slight increase (~7%) of its amplitude with count rate. The RMS-spectra of the two peaks are quite different. The ~3 Hz feature is softer than the other one, and shows a cut-off at an energy of ~6 keV while the RMS of the 6 Hz increases up to at least 20 keV. We also study the bicoherence, $b^2(\mu ,\nu )$. The values b^2(~3,~3) and b^2(~6,~6) are rather high and similar to the type C QPOs of GRS 1915+105. By comparison with the latter source the fact that the bicoherence of the ~3 Hz feature is higher than that of the other peak, would tend to indicate that the ~3 Hz is the fundamental QPO. The value of b^2(~3,~6)$ is, however, low and therefore indicates a behavior that is different than that seen in GRS 1915+105. We suggest that, rather than pure harmonics, we may see different modes of the same underlying phenomenon competing to produce QPOs at different frequencies.

7 pages, 5 figures, published in ApJ, vol 735, p79 Version corrected for small mistakes

References in corpus (3)

• X-ray Properties of Black-Hole Binaries
• Two Years of INTEGRAL monitoring of GRS 1915+105 Part 2: X-Ray Spectro-Temporal Analysis
• Coupling between QPOs and broadband noise components in GRS 1915+105

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• Fast transition of type-B QPO in the black hole transient XTE J1817-330
• The Relationship Between X-ray Luminosity and Major Flare Launching in GRS 1915+105
• Disc-corona interaction in the heartbeat state of GRS 1915+105
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• On the modulation of low frequency Quasi-Periodic Oscillations in black-hole transients
• Phase-Resolved Timing Analysis of GRS 1915+105 in Its ρ State