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The Island State of the Atoll Source 4U 1820-30
Altamirano, Diego; Van der Klis, M.; Méndez, M.; Migliari, Simone; Jonker, P. G.; Tiengo, A.; Zhang, W.
Universitat de Barcelona
We study the rapid X-ray time variability in all public data available from the Rossi X-Ray Timing Explorer Proportional Counter Array on the atoll source 4U 1820-30 in the low-luminosity island state. A total of ~46 ks of data were used. We compare the frequencies of the variability components of 4U 1820-30 with those in other atoll sources. These frequencies were previously found to follow a universal scheme of correlations. We find that 4U 1820-30 shows correlations that are shifted by factors of 1.13 ± 0.01 and 1.21 ± 0.02 with respect to those in other atoll sources. These shifts are similar to, but smaller than, the shift factor of ~1.45 previously reported for some accreting millisecond pulsars. Therefore, 4U 1820-30 is the first atoll source that shows no significant pulsations but has a significant shift in the frequency correlations compared with the other three nonpulsating atoll sources.
Estels binaris de raigs X
Estels de neutrons
Astronomia de raigs X
X-ray binaries
Neutron stars
X-ray astronomy
(c) American Astronomical Society, 2005
Institute of Physics (IOP)

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