We use the observed optical-UV and X-ray emission spectrum of Cen X-4 during quiescence to constrain models for the accretion flow in this system. We argue that the optical-UV emission is not due to an optically thick quiescent accretion disk, nor due to synchrotron emission from an advection-dominated accretion flow (ADAF). Emission from the bright spot could account for the observed optical-UV component if the mass transfer rate in Cen X-4 is 2 × 1016 g s-1. Although the presence of an ADAF around the neutron star leads to Compton upscattering of the soft X-ray photons radiated from the stellar surface, we find that this process alone cannot account for the power-law component seen in the quiescent X-ray spectrum of Cen X-4 and other X-ray transients containing neutron stars; this result is independent of whether the source of soft photons is incandescent thermal emission or accretion-powered emission. We conclude that, in models which invoke the presence of an ADAF and a propeller effect for the quiescence of X-ray transients containing neutron stars, the intrinsic emission from the ADAF must contribute very little to the optical-UV and X-ray emission observed. If these ADAF + propeller models are correct, the X-ray power-law component observed must arise from regions where the gas impacts the neutron star surface. Variability studies could greatly help clarify the role of the various emission mechanisms involved.
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机译：我们使用静态时观测到的Cen X-4的光学UV和X射线发射光谱来约束该系统中吸积流的模型。我们认为，紫外光发射不是由于光学上较厚的静态吸积盘，也不是由于平流为主的吸积流（ADAF）产生的同步加速器发射。如果Cen X-4中的传质速率为2×1016 g s-1，则亮点的发射可解释观察到的光学UV分量。尽管在中子星周围存在ADAF会导致从恒星表面辐射的软X射线光子的康普顿散射，但我们发现仅此过程不能解释在静态X射线光谱中看到的幂律分量。 Xen X-4和其他含有中子星的X射线瞬变;此结果与软光子源是白炽热发射还是增生动力发射无关。我们得出的结论是，在调用存在ADAF和螺旋桨效应以使包含中子星的X射线瞬态静止的模型中，ADAF的固有发射对观察到的光学UV和X射线发射的贡献很小。 。如果这些ADAF +螺旋桨模型正确，则观察到的X射线幂律分量必须来自气体影响中子星表面的区域。可变性研究可以极大地帮助阐明所涉及的各种排放机制的作用。
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