LOW-FREQUENCY OSCILLATIONS IN XTE J1550-564
- INAF-Osservatorio Astronomico di Brera, Via E. Bianchi 46, I-23807 Merate (Italy)
- INAF-Osservatorio Astronomico di Roma, Via di Frascati 33, I-00040 Monteporzio Catone, Rome (Italy)
- Department of Physics and Center for Astrophysics, Tsinghua University, Beijing 100084 (China)
We present the results of a timing analysis of the low-frequency quasi-periodic oscillation (QPO) in the Rossi X-Ray Timing Explorer data of the black hole binary XTE J1550-564 during its 1998 outburst. The QPO frequency is observed to vary on timescales between {approx}100 s and days, correlated with the count rate contribution from the optically thick accretion disk: we studied this correlation and discuss its influence on the QPO width. In all observations, the quality factors ({nu}{sub 0}/FWHM) of the fundamental and second harmonic peaks were observed to be consistent, suggesting that the quasi-periodic nature of the oscillation is due to frequency modulation. In addition to the QPO and its harmonic peaks, a new 1.5{nu} component was detected in the power spectra. This component is broad, with a quality factor of {approx}0.6. From this, we argue that the peak observed at half the QPO frequency, usually referred to as 'sub-harmonic', could be the fundamental frequency, leading to the sequence 1:2:3:4. We also studied the energy dependence of the timing features and conclude that the two continuum components observed in the power spectrum, although both more intense at high energies, show a different dependence on energy. At low energies, the lowest-frequency component dominates, while at high energies the higher-frequency one has a higher fractional rms. An interplay between these two components was also observed as a function of their characteristic frequency. In this source, the transition between the low/hard state and the hard-intermediate state appears to be a smooth process.
- OSTI ID:
- 21448877
- Journal Information:
- Astrophysical Journal, Vol. 714, Issue 2; Other Information: DOI: 10.1088/0004-637X/714/2/1065; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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