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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    The astronomy and astrophysics review 1 (1989), S. 85-110 
    ISSN: 1432-0754
    Keywords: black holes ; X-rays: binaries ; stars: neutron ; stars: Be ; stars: mass loss
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The various types and classes of X-ray binary are reviewed high-lighting recent results. The high mass X-ray binaries (HMXRBs) can be used to probe the nature of the mass loss from the OB star in these systems. Absorption measurements through one orbital cycle of the supergiant system X1700-37 are well modelled by a radiation driven wind and also require a gas stream trailing behind the X-ray source. In Cen X-3 the gas stream is accreted by the X-ray source via an accretion disk. Changes in the gas stream can cause the disk to thicken and the disk to obscure the X-ray source. How close the supergiant is to corotation seems to be as much a critical factor in these systems as how close it is to filling its Roche lobe. In the Be star X-ray binaries a strong correlation between the neutron stars rotation period and its orbital period has been explained as due to the neutron star being immersed in a dense, slow moving equatorial wind from the Be star. For the X-ray pulsars in the transient Be X-ray binaries a centrifugal barrier to accretion is important in determining the X-ray lightcurve and the spin evolution. The X-ray orbital modulations from the low mass X-ray binaries, LMXRBs, include eclipses by the companion and/or periodic dipping behaviour from structure at the edge of the disk. The corresponding optical modulations show a smooth sinusoidal like component and in some cases a sharp eclipse by the companion. The orbital period of the LMXRB XB1916-05 is 1% longer in the optical compared to that given by the X-ray dip period. The optical period has been interpreted as the orbital period, but this seems inconsistent with the well established view of the origin of the X-ray modulations in LMXRB. A new model is presented that assumes the X-ray dip period is the true orbital period. The 5.2 h eclipsing LMXRB XB2129+47 recently entered a low state and optical observations unexpectedly reveal an F star which is too big to fit into the binary. This is probably the first direct evidence that an X-ray binary is part of a hierarchical triple. Finally the class of X-ray binaries containing black hole candidates is reviewed focusing on the value of using X-ray signatures to identify new candidates.
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 336 (1988), S. 424-425 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] THREE years have passed since the discovery1 of 20-50-hertz quasiperiodic oscillations (QPOs) from the bright X-ray source in the Galactic Centre, GX5-1. This discovery, made using the European Space Agency's Exosat satellite observa-tory, may provide the first direct indication that this class of ...
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 313 (1985), S. 119-121 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Hercules X-1 (Her X-1) was observed by the European Space Agency's EXOSAT Observatory (see ref. 12 for additional details) on 1983 June 28, 37 days after the Tenma X-ray satellite observed that it was close to its maximum high-state intensity13. During the 35-day cycle, Her X-1 normally has a ...
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 319 (1986), S. 469-471 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Observations of Cyg X-2 (4U 2142 + 380) with the Exosat instruments termed the medium energy experiment7 (ME) and gas scintillation proportional counter8 (GSPC) were carried out during a 14 h period beginning at 02:07 UT on 23 July, 1984. One half of the ME monitored the background. ME data were ...
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  • 5
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 316 (1985), S. 210-211 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] THE first short timescale periodic oscillations from a bright galactic centre X-ray source (GX5?1) are reported by van der Klis et al. on page 225 of this issue. These quasi-periodic oscillations (QPOs) probably indicate the presence of an accreting neutron star that is rotating with a period of a ...
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  • 6
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 333 (1988), S. 708-708 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] ELSEWHERE in this issue, K. Makishima et al. (Nature 333, 746-748; 1988) report that the spin-rate of the X-ray pulsar GX1 +4, which they have been observing with the X-ray satellite Ginga, is now decreasing whereas previous observations had shown that it was increasing. This fits neither of the ...
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  • 7
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 332 (1988), S. 416-418 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] An accreting, magnetized neutron star will be spun-up by the angular momentum of the accreted material until its rotation period equals the last keplerian period of the accretion disk at the magnetosphere boundary. If the neutron star rotates faster than this equilibrium period, the centrifugal ...
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Space science reviews 40 (1985), S. 167-194 
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The present knowledge of the structure of low-mass X-ray binary systems is reviewed. We examine the orbital period distribution of these sources and discuss how the orbital periods are measured. There is substantial observational evidence that the accretion disks in low-mass X-ray binaries are thick and structured. In a number of highly inclined systems, the compact X-ray emitting star is hidden from direct view by the disk and X-radiation is observed from these only because photons are scattered into the line of sight by material above and below the disk plane. In such systems the X-ray emission can appear extended with respect to the companion star, which can lead to partial X-ray eclipses. There are substantial variations in the thickness of the disk rim with azimuth. These give rise to the phenomenon of irregular dips in the X-ray flux which recur with the orbital period, or to an overall binary modulation of the X-ray flux if the source is “extended”. The X-ray spectra of low-mass X-ray binaries can be used to probe the innermost emission regions surrounding the compact star. The spectra of the bright “Sco X-1” variables can be fitted with two components which are provisionally identified as originating in the inner disk and the boundary layer between the disk and the neutron star respectively. The characteristic energy dependent flaring of the “Sco X-1” sub-class may be a geometric effect triggered by an increase in the thickness of the inner disk or boundary layer. The X-ray spectra of the lower luminosity systems, including the bursters, are less complex, and in many cases can be represented by a single power law with, in some sources, a high energy cut-off. Iron line emission is a characteristic of most low-mass X-ray binaries, irrespective of luminosity.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Space science reviews 40 (1985), S. 383-386 
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary We present the results of seven observations of the X-ray spectrum of Cyg X-1, made with the GSPC on board the EXOSAT observatory. We report the discovery of an iron emission line in its spectrum. The likely origin of this feature is discussed.
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  • 10
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The X-ray emission from Algol is thought to originate in a corona associated with the K star in this system. We report the results of a 35 hr continuous EXOSAT observation through secondary optical eclipse that was designed to measure the structure of the corona. No obvious X-ray eclipse was seen. The spectrum measured by the ME gives a temperature of 2.5 × 107 K, consistent with the hard component previously seen by the Einstein SSS. The soft component previously reported by the SSS would only contribute at most 25% to the count rate seen in the LE (used with Al/P). The lack of a hard X-ray eclipse indicates the dimensions of the higher temperature emission region to be comparable to or greater than the size of the K star. An X-ray flare was detected with a peak luminosity of 1.4 × 1031 erg s-1 and a total duration of 8 hours. The peak temperature was 5.0 keV with an emission measure of 9.4 × 1053 cm-3. The thermal nature of the flare is confirmed by the detection of an iron line with an EW of ∼2 keV. By equating the observed decay time of the flare to a known cooling law gives a dimension for the flaring loop of ∼0.3 stellar radii. This is much smaller than the dimensions of the hard component inferred from the lack of an eclipse. It seems probable that the flare occurred in one of the loops responsible for the lower temperature component seen by the SSS.
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