Rudy A. D. Wijnands

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Millisecond pulsars are neutron stars that are thought to have been spun-up by mass accretion from a stellar companion. It is not known whether there is a natural brake for this process, or if it continues until the centrifugal breakup limit is reached at submillisecond periods. Many neutron stars that are accreting mass from a companion star exhibit(More)
We measure simultaneously the properties of the energy spectra and the frequencies of the kilohertz quasi-periodic oscillations (QPOs) in fifteen low mass X-ray binaries covering a wide range of X-ray luminosities. In each source the QPO frequencies cover the same range of approximately 300 Hz to 1300 Hz, though the sources differ by two orders of magnitude(More)
We present new results based on observations carried out with the Rossi X-ray Timing Explorer during the decay of an outburst of the low-mass X-ray binary (LMXB) and atoll source 4U 1608–52. Our results appear to resolve, at least in 4U 1608–52, one of the long-standing issues about the phenomenology of the kilohertz quasi-periodic oscillations (kHz QPOs),(More)
Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. ABSTRACT We report on six RXTE observations taken during the 2010 outburst of(More)
We report on a series of 20, 110 5 counts s Ϫ1 , 0.125 ms time-resolution Rossi X-Ray Timing Explorer observations of the Z-source and low-mass X-ray binary Scorpius X-1. Twin kilohertz quasi-periodic oscillation (QPO) peaks are obvious in nearly all observations. We find that the peak separation is not constant, as expected in some beat-frequency models,(More)
We report the discovery of nearly coherent oscillations with a frequency of ∼ 567 Hz during type-I X-ray bursts from the X-ray transient and eclipsing binary X 1658–298. If these oscillations are directly related to the neutron star rotation then the spin period of the neutron star in X 1658–298 is ∼1.8 ms. The oscillations can be present during the rise or(More)
We present new Rossi X-ray Timing Explorer observations of the low-mass X-ray binary 4U 1608–52 during the decay of its 1998 outburst. We detect by a direct FFT method the existence of a second kilohertz quasi-periodic oscillation (kHz QPO) in its power density spectrum, previously only seen by means of the sensitivity-enhancing 'shift and add' technique.(More)
We present an analysis of data of the black hole candidate and X-ray transient XTE J1550–564, taken with the Rossi X-ray Timing Explorer between 1998 November 22 and 1999 May 20. During this period the source went through several different states, which could be divided into soft and hard states based on the relative strength of the high energy spectral(More)
I present an overview of our current observational knowledge of the six known accretion-driven millisecond X-ray pulsars. A prominent place in this review is given to SAX J1808.4–3658; it was the first such system discovered and currently four outbursts have been observed from this source, three of which have been studied in detail using the Rossi X-ray(More)
We present Chandra and XMM–Newton X-ray observations that monitor the neutron star cooling of the quasi-persistent neutron star X-ray transients KS 1731−260 and MXB 1659−29 for approximately 4 yr after these sources returned to quiescence from prolonged outbursts. In both sources the outbursts were long enough to significantly heat the neutron star crust(More)