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A transient high-coherence oscillation in 4U 1820-30

T. Belloni·I. Parolin·P. Casella
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Abstract

We re-analyzed two Rossi X-Ray Timing Explorer archival observations of the atoll source 4U 1820-30 in order to investigate the detailed time-frequency properties of the source during the intervals when a ~7 Hz QPO was detected by Wijnands et al. (1999, ApJ, 512, L39). We find that in both observations, in addition to a QPO signal lasting a couple of minutes as previously reported, there is a much narrower transient oscillation with a life time of only a few seconds. Within this time, the oscillation is consistent with being coherent. Its integrated fractional rms is around 10% and its frequency 7.3 Hz and 5.7 Hz in the two observations. We discuss the possible association of this QPO with other oscillations known both in Neutron-Star and Black-Hole systems, concentrating on the similarities with the narrow 5-7 Hz oscillations observed at high flux in Black-Hole Candidates.

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T. Belloni, I. Parolin, P. Casella. 2004-05-17. A transient high-coherence oscillation in 4U 1820-30. https://doi.org/10.1051/0004-6361%3A20040335

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