Coherence between QPOs in X-ray Pulsars

Abstract:

Rossi X-ray Timing Explorer (RXTE) observations of Cen X-3 and 4U 1626-67 have shown that when a low frequency (nu_qpo~ 50 mHz) Quasi-Periodic Oscillation (QPO) is present in the power spectrum of these sources, smaller QPOs also appear in the upper and lower sidebands of the spin frequency nu_s, and in the sidebands of spin frequency harmonics. This is expected if the QPO is a modulation in the accretion rate. However, the QPO in the lower sideband of the spin frequency (nu= nu_s-nu_qpo) is stronger than the QPO in the in the upper sideband (nu= nu_s+ nu_qpo), which is not consistent with pure accretion rate modulation. I will present a method for measuring the phase coherence between the main QPO and any of the sideband QPOs, and apply this to RXTE observations. Preliminary results for Cen X-3 show that the QPO in the lower sideband of the spin frequency is highly coherent with the main …

Año de publicación:

1999

Keywords:

Fuente:

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