Strong Aperiodic X-Ray Variability and Quasi-Periodic Oscillationin X-Ray Nova XTE J1550-564
Abstract
We report the discovery of strong aperiodic X-ray variability and quasi-periodic oscillation (QPO) in the X-ray light curves of a new X-ray nova, XTE J1550-564, and the evolution of the observed temporal properties during the rise of the recent X-ray outburst. The power spectral analysis of the first observation reveals strong aperiodic X-ray variability of the source (~28%) as well as the presence of a QPO at ~82 mHz with fractional rms amplitude ~14% over the 2-60 keV energy range. Also apparent is the first harmonic of the QPO with the amplitude ~9%. As the X-ray flux increases, the source tends to become less variable, and the QPO frequency increases rapidly, from 82 mHz to 4 Hz, over the flux (2-50 keV) range of 1.73-5.75×10-8 ergs cm-2 s-1. The amplitude of the fundamental component of the QPO varies little, while that of the harmonic follows a decreasing trend. The fundamental component strengthens toward high energies, while its harmonic weakens. Initially, the power spectrum is roughly flat at low frequencies and turns into a power law at high frequencies, with the QPO harmonic sitting roughly at the break. In later observations, however, the high-frequency portion of the continuum can actually be better described by a broken power law (as opposed to a simple power law). This effect becomes more apparent at higher energies. The overall amplitude of the continuum shows a similar energy dependence to that of the fundamental component of the QPO. Strong rapid X-ray variability, as well as a hard energy spectrum, makes XTE J1550-564 a good black hole candidate. We compare its temporal properties with those of other black hole candidates.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 1999
- DOI:
- 10.1086/311870
- arXiv:
- arXiv:astro-ph/9812308
- Bibcode:
- 1999ApJ...512L..43C
- Keywords:
-
- STARS: BINARIES: GENERAL;
- STARS: INDIVIDUAL: ALPHANUMERIC: XTE J1550-564;
- X-RAYS: STARS;
- Stars: Binaries: General;
- Stars: Individual: Alphanumeric: XTE J1550-564;
- X-Rays: Stars;
- Astrophysics
- E-Print:
- 12 pages, including 5 figures. To appear in ApJ Letters, vol. 512 (1999)