High-Energy Astrophysics American and Soviet Perspectives/Proceedings from the U.S.-U.S.S.R. Workshop on High-Energy Astrophysics (1991) / Chapter Skim
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QUASI-PERIODIC OSCILLATIONS IN LOW-MASS X-RAY BINARIES
QUASI-PERIODIC OSCILLATIONS IN LOW-MASS X-RAY BINARIES
Pages 251-260
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From page 251... ...
An outstanding exception has been the study of the very fast variability of the black-hole candidate Cyg X-1 and sources long thought to be of a similar nature such as Cir X-1 and GX 3394 (for a comprehensive review of the studies of noise in X-ray intensity variations of binary X-ray sources up to 1980, we refer to Bradt et at 1982~. Consequently the bright persistent X-ray sources in the central regions of the Galaxy (the galactic bulge sources)
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From page 252... ...
between the Keplerian frequency at the inner disk edge and the neutron star spin frequency. Modulation of the accretion rate through magnetic gating was proposed as a feasible mechanism for causing the X-ray intensity variations, and it was shown that the red-noise component was a natural consequence of accretion-modulation mechanism (Lamb e!
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From page 253... ...
The lines drawn through the data indicate fits described lay a function which is the sum of a constant (Poisson noise) , a line with a Lorentzian profile (the QPO peak)
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From page 254... ...
Three of the newly discovered QPO sources were known to exhibit two different X-ray spectral states, distinguishable as "branches" in an X-ray hardness versus intensity diagram. In OX 5-1 the 2040 Hz QPO were only and always observed when the source was found in the so-called "horizontal-branch" of this diagram (Van der Klis et al.
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The solid dots in the "honzontal branch" (HB) represent data when strong 2040 Hz QPO were observed; the power spectra represented by open circles on the "normal branch" (NB)
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From page 256... ...
1' 10-3 10-2 io-i 10 ° 101 ~o2 FREQUENCY (Hz) FIGURE 3 Display of the X-ray color color diagrams and power spectra for the Z sources C;yg X-2 and GX 17 + 2 illustrating the Correlation between the QPO behavior and the location of the source on the Z-shaped track This figure has been adapted from Van der Klis (1989~.
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From page 257... ...
When these sources are in the haring-branch state their radio brightness is relatively low, it increases when the source moves up the normal branch, becoming relatively high on the horizontal branch Since the radio emission is probably caused by relativistic electrons (synchrotron radiation) , this correlation suggests that perhaps the required non-thermal processes and particle acceleration are connected with the boundary layer between the inner disk and the magnetosphere of the neutron star.
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From page 258... ...
FIGURE 4 Display of the X-ray color color diagrams and power spectra of the atoll sources GX 13 ~ 1 and 4U 170544 illustrating the oo:Telation between power spectrum and the source spectral state ("island" versus "banana" state)
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From page 259... ...
al. (19891 mav Dose problems for He beat frequency model ~, ~ In closing, the recent division of the low-mass X-ray binaries in Z sources and atoll sources has clarified matters a great deal.
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From page 260... ...
Van der Klis.
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