2007ApJ...663.1225B -
Astrophys. J., 663, 1225-1231 (2007/July-2)
Correlations between X-ray spectral characteristics and quasi-periodic oscillations in Scorpius X-1.
BRADSHAW C.F., TITARCHUK L. and KUZNETSOV S.
Abstract (from CDS):
Correlations between 1-10 Hz quasi-periodic oscillations (QPOs) and spectral power-law index have been reported for black hole (BH) candidate sources and one neutron star source, 4U 1728-34. An examination of QPO frequency and index relationships in Sco X-1 is reported here. We discover that Sco X-1, representing Z-source groups, can be adequately modeled by a simple two-component model of Compton up-scattering with a soft photon electron temperature of about 0.4 keV, plus an Iron K line. The results show a strong correlation between spectral power-law index and kHz QPOs. Because Sco X-1 radiates near the Eddington limit, one can infer that the geometrical configuration of the Compton cloud (CC) is quasi-spherical from high radiation pressure in the CC. Thus, we conclude that the high Thomson optical depth of the Compton cloud, in the range of ∼5-6 from the best-fit model parameters, is consistent with the neutron star's surface being obscured by material. Moreover, a spin frequency of Sco X-1 is likely suppressed due to photon scattering off CC electrons. In addition, we demonstrate how the power spectrum evolves when Sco X-1 transitions from the horizontal branch to the normal branch.
Abstract Copyright:
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Journal keyword(s):
Accretion, Accretion Disks - Stars: Individual: Constellation Name: Scorpius X-1 - Stars: Neutron - X-Rays: Individual: Constellation Name: Scorpius X-1
Simbad objects:
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