We present Hubble Space Telescope/Advanced Camera for Surveys ultraviolet photometry of three quiescent black hole X-ray transients, X-ray Nova Muscae 1991 (GU Mus), GRO J0422+32 (V518 Per), and X-ray Nova Vel 1993 (MM Vel), and one neutron star system, Aql X-1. These are the first quiescent UV detections of these objects. All are detected at a much higher level than expected from their companion stars alone and are significant detections of the accretion flow. Three of the four UV excesses can be characterized by a blackbody of temperature 5000-13, 000?K, hotter than expected for the quiescent outer disk. A good fit could not be found for MM Vel. The source of the blackbody-like emission is most likely a heated region of the inner disk. Contrary to initial indications from spectroscopy, there does not appear to be a systematic difference in the UV luminosity or spectral shape between black holes and neutron star systems. However, combining our new data with earlier spectroscopy and published X-ray luminosities, there is a significant difference in the X-ray to UV flux ratios, with the neutron stars exhibiting L X/L UV about 10 times higher than the black hole systems. This is consistent with earlier comparisons based on estimating non-stellar optical light, but since both bandpasses we use are expected to be dominated by accretion light, we present a cleaner comparison. This suggests that the difference in X-ray luminosities cannot simply reflect differences in quiescent accretion rates and so the UV/X-ray ratio is a more robust discriminator between the black hole and neutron star populations than the comparison of X-ray luminosities alone.
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机译：我们介绍了哈勃太空望远镜/高级相机，用于对三个静态黑洞X射线瞬变，X射线Nova Muscae 1991（GU Mus），GRO J0422 + 32（V518 Per）和X射线Nova Vel 1993（ MM Vel）和一个中子星系统Aql X-1。这些是这些对象的第一个静态UV检测。探测到的所有卫星都比单独观测其伴星的预期水平高得多，并且是对积聚流的重要探测。四个紫外线过剩中的三个可以通过温度为5000-13，000？K的黑体来表征，该黑体的温度高于静态外盘的预期温度。找不到适合MM Vel的合适装备。黑体状发射的来源很可能是内盘的受热区域。与光谱学的初步发现相反，黑洞和中子星系统之间的紫外光度或光谱形状似乎没有系统的差异。但是，将我们的新数据与较早的光谱学和已发布的X射线光度相结合，X射线与UV的通量比存在显着差异，中子星表现出的L X / L UV约为黑洞系统的10倍。这与先前基于估计非星状光学光的比较是一致的，但是由于我们使用的两个带通都被吸积光所主导，因此我们提出了一个比较清晰的比较。这表明X射线光度的差异不能简单地反映静态吸积率的差异，因此与单独比较X射线光度相比，UV / X射线比是黑洞与中子星总数之间更强的区分力。
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