The Medium Energy Instrument on Exosat

Turner, M. J. L.; Smith, A.; Zimmermann, H. U.

doi:10.1007/bf01246071

Cited by 109 publications

(28 citation statements)

References 1 publication

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“…For our analysis we used Cyg X-1 and Cyg X-2 data from the Proportional Counter Array (PCA) and All-Sky Monitor (ASM ) on board RXTE (Swank 1999) and the medium energy ( ME) detector of EXOSAT (Turner et al 1981). The data are available through the Goddard Space Flight Center public archive.…”

Section: Observationsmentioning

confidence: 99%

Power Spectra of Black Holes and Neutron Stars as a Probe of Hydrodynamic Structure of the Source: Diffusion Theory and Its Application to Cygnus X‐1 and Cygnus X‐2 X‐Ray Observations

Titarchuk

Shaposhnikov

Arefiev

2007

ApJ

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We present a model of Fourier power density spectrum ( PDS) formation in accretion-powered X-ray binary systems derived from diffusion theory. Timing properties of X-ray emission are considered a result of diffusive propagation of the driving perturbations in a bounded medium. We prove that the integrated power P x of the resulting PDS is only a small fraction of the integrated power P dr of the driving oscillations, which is distributed over the disk. Furthermore, we demonstrate that P x is inversely proportional to the characteristic frequency of the driving oscillations dr , which likely scales with the frequency of the local gravity waves in the disk (Keplerian frequency). Because dr increases toward soft states, we conclude that P x declines toward soft states. This dependence P x / À1 dr explains the well-known observational phenomenon that the X-ray variability power decreases when the source evolves to softer states. The resulting PDS continuum is a sum of a low-frequency (LF) component, which presumably originates in an extended accretion disk, and a high-frequency ( HF) component, which originates in the innermost part of the source (Compton cloud or corona). The LF PDS component has a power-law shape with an index of 1.0Y1.5 at higher frequencies (''red'' noise) and a flat spectrum below a characteristic ( break) frequency (''white'' noise). This white-red noise (WRN ) continuum spectrum holds information about the bounded extended medium, the diffusion timescale, and the dependence law of viscosity versus radius. We apply our model of the PDS to RXTE and EXOSAT timing data from Cygnus X-1 and Cygnus X-2, which describes adequately the spectral transitions in these sources. The presented PDSs are shown in frequency range from 10 À8 to 10 2 Hz, 10 orders of magnitude.

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Section: Observationsmentioning

confidence: 99%

Power Spectra of Black Holes and Neutron Stars as a Probe of Hydrodynamic Structure of the Source: Diffusion Theory and Its Application to Cygnus X‐1 and Cygnus X‐2 X‐Ray Observations

Titarchuk

Shaposhnikov

Arefiev

2007

ApJ

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“…subtracted; deadtime correction has not been applied. Data for the Rapid Burster is the 1-20 keV count rate in the EXOSAT/ME instrument (Turner, Smith, & Zimmermann 1981), with a nominal background count rate of 70 counts s Ϫ1 subtracted; no deadtime correction has been applied. Time resolution of the data shown is 2 s. The vertical scale has been enlarged, cutting off the peak count rates of the bursts, to show the postburst ''dips'' in some detail.…”

Section: Gro J1744ϫ28mentioning

confidence: 99%

A Comparison between the Rapid Burster and GRO J1744–28

Lewin

Rutledge

Kommers

et al. 1996

ApJ

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A comparison between the rapid burster and GRO J1744-28Lewin, W.H.G.; Rutledge, R.E.; Kommers, J.M.; van Paradijs, J.A.; Kouveliotou, C. General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. ABSTRACT Twenty years ago, the Rapid Burster (MXB 1730Ϫ335) was discovered. Its most salient feature was the occurrence of rapidly repetitive type II X-ray bursts, the release of gravitational potential energy due to spasmodic accretion onto a compact object. This is almost certainly due to an accretion disk instability whose origin is still not understood. With the recent appearance of GRO J1744Ϫ28, the Rapid Burster is no longer the only system to produce such bursts. Both systems are transient low-mass X-ray binaries in which the accretor is a neutron star. The Rapid Burster, located in a globular cluster, also produces type I bursts which are due to thermonuclear flashes on the neutron star's surface; no X-ray pulsations are observed. Its neutron star magnetic field is therefore relatively weak. In contrast, strong X-ray pulsations have been observed in the persistent flux as well as in the type II bursts from GRO J1744Ϫ28, but no type I bursts have been observed. Thus, the magnetic field of the neutron star in this system is probably stronger than is the case of the Rapid Burster. The fact that type II bursts occur in both systems may bring us closer to an understanding of the mechanism(s?) that produces them. Subject headings: stars: neutron -X-rays: general -X-rays: bursts THE RAPID BURSTERThe Rapid Burster (MXB 1730Ϫ335) was discovered in March of 1976 during observations with the SAS 3 observatory (Lewin et al. 1976). Extensive reviews of this source and its complex behavior are given by Lewin, Van Paradijs, & Taam (1993, 1995; these two reviews are hereafter referred to as LVT93, LVT95. We mention here some of the most salient features of the Rapid Burster and refer the reader largely to LVT93 and LVT95 for references.The Rapid Burster is located at a distance of 110 kpc in the highly reddened globular cluster Liller 1. It is a low-mass X-ray binary and a recurrent transient. There are 1125 known low-mass X-ray binaries (van Paradijs 1995), all produce a persistent flux of X-rays, the result of a release of gravitational potential energy. Approximately 40 of them also ex...

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“…We downloaded 1-8 keV background-subtracted EXOSAT light curves from the medium energy (ME) proportional counter (Turner, Smith, & Zimmermann 1981) with 1 s time resolution from the High-Energy Astrophysics Science Archive Research Center (HEASARC) 5 at Goddard Space Flight Center for 14 EXOSAT observations (see Parmar et al 1989b for observation details). We were unable to unambiguously maintain a pulsar cycle count across these observations, so we measured pulse frequencies instead.…”

Section: Orbit Fittingmentioning

confidence: 99%

A Decade in the Life of EXO 2030+375: A Multiwavelength Study of an Accreting X‐Ray Pulsar

Wilson

Finger

Coe

et al. 2002

ApJ

155

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Using BATSE and RXTE observations from 1991 April to 2001 August, we have detected 71 outbursts from 82 periastron passages of EXO 2030+375, a 42 s transient X-ray pulsar with a Be star companion, including several outbursts from 1993 August to 1996 April, when the source was previously believed to be quiescent. Combining BATSE, RXTE, and EXOSAT data, we have derived an improved orbital solution. Applying this solution results in a smooth profile for the spin-up rate during the giant outburst and results in evidence for a correlation between the spin-up rate and observed flux in the brighter BATSE outbursts. Infrared and H measurements show a decline in the density of the circumstellar disk around the Be star. This decline is followed by a sudden drop in the X-ray flux and a turnover from a spin-up trend to spin-down in the frequency history. This is the first Be/X-ray binary that shows an extended interval, about 2.5 yr, in which the global trend is spin-down, but the outbursts continue. In 1995 the orbital phase of EXO 2030+375's outbursts shifted from peaking about 6 days after periastron to peaking before periastron. The outburst phase slowly recovered to peaking at about 2.5 days after periastron. We interpret this shift in orbital phase followed by a slow recovery as evidence of a global one-armed oscillation propagating in the Be disk. This is further supported by changes in the shape of the H profile, which are commonly believed to be produced by a reconfiguration of the Be disk. The truncated viscous decretion disk model provides an explanation for the long series of normal outbursts and the evidence of an accretion disk in the brighter normal outbursts. Longterm multiwavelength observations such as these clearly add considerably to our knowledge of Be/X-ray binaries and the relationship among optical, infrared, and X-ray observations.

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The Medium Energy Instrument on Exosat

Cited by 109 publications

References 1 publication

Power Spectra of Black Holes and Neutron Stars as a Probe of Hydrodynamic Structure of the Source: Diffusion Theory and Its Application to Cygnus X‐1 and Cygnus X‐2 X‐Ray Observations

Power Spectra of Black Holes and Neutron Stars as a Probe of Hydrodynamic Structure of the Source: Diffusion Theory and Its Application to Cygnus X‐1 and Cygnus X‐2 X‐Ray Observations

A Comparison between the Rapid Burster and GRO J1744–28

A Decade in the Life of EXO 2030+375: A Multiwavelength Study of an Accreting X‐Ray Pulsar

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