Observations of 1.4-Hz quasi-periodic oscillations in Cir X-1
Open Access
- 1 February 1988
- journal article
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 230 (3) , 403-414
- https://doi.org/10.1093/mnras/230.3.403
Abstract
Cir X-1 was observed to vary by a factor of ∼1000 during an EXOSAT observation made in August 1985. The power spectrum is ∼ 1/f from ∼10−5 to ∼0.02 Hz. Above 0.02 Hz the power spectrum steepens. In this paper, results from the interval in which the source flux increased to the maximum are presented. During this interval the source was highly variable on time-scales of > 1 s. The lack of high-frequency noise and the shape of the energy spectrum favor a model in which most of this variability is due to obscuration of the central source. Quasi-periodic oscillation (QPO) were detected at a frequency of 1.4 Hz. There was no indication of a change in the peak frequency as the intensity varied by a factor > 3. When compared to a previously published observation of Cir X-1, we find evidence that the QPO is bimodal with the low-frequency being independent of intensity.Keywords
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