Rossi XTE monitoring of 4U 1636–53 – I. Long-term evolution and kHz quasi-periodic oscillations |
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| Authors: | T Belloni J Homan S Motta E Ratti M Méndez |
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| Institution: | INAF-Osservatorio Astronomico di Brera, Via E. Bianchi 46, I-23807 Merate (LC), Italy;MIT Kavli Institute for Astrophysics and Space Research, 70 Vassar Street, Cambridge, MA 02139, USA;Universitàdi Milano Bicocca, Piazza della Scienza 3, 20126 Milano, Italy;SRON, Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, the Netherlands;Astronomical Institute 'Anton Pannekoek', University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, the Netherlands;Astronomical Institute, University of Utrecht, PO Box 80000, 3508 TA Utrecht, the Netherlands |
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| Abstract: | We have monitored the atoll-type neutron star low-mass X-ray binary 4U 1636?53 with the Rossi X-ray Timing Explorer ( RXTE ) for more than 1.5 yr. Our campaign consisted of short (～2 ks) pointings separated by 2 d, regularly monitoring the spectral and timing properties of the source. During the campaign we observed a clear long-term oscillation with a period of ～30–40 d, already seen in the light curves from the RXTE All-Sky Monitor, which corresponded to regular transitions between the hard (island) and soft (banana) states. We detected kilohertz (kHz) quasi-periodic oscillations (QPOs) in about a third of the observations, most of which were in the soft (banana) state. The distribution of the frequencies of the peak identified as the lower kHz QPO is found to be different from that previously observed in an independent data set. This suggests that the kHz QPOs in the system shows no intrinsically preferred frequency. |
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| Keywords: | accretion accretion discs stars: neutron X-rays: binaries |
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