半人马座A尘埃带中的一个瞬态亚爱丁顿黑洞候选X射线双星
A Transient Sub-Eddington Black Hole X-ray Binary Candidate in the Dust Lanes of Centaurus A
摘要：
本文报道了在早型星系NGC 5128中发现的一个明亮的X射线瞬变源CX132527.6 -430023。在2007年钱德拉的五次观测过程中首次发现了该源，在0.5-7.0 keV波段达到1-2*10^38 erg/s的未吸收爆发光度，然后恢复平静。这样的光度对于恒星质量的黑洞和中子星X射线双星瞬变都是可能的。在这里，我们试图描述紧凑对象的性质。在光学或无线电天空中还没有发现对应的物质，但由于该物质与尘埃带的距离很近，因此有可能存在一个被遮蔽的伴星。在X射线通量增加100倍以上后，该源的亮度使其成为第一个被证实的在爆发中的瞬态非ULX黑洞系统，以在本星系群之外进行详细的光谱建模，或者是一个明亮的（>10^38 erg/s）瞬态中子星X射线双星，这是非常罕见的。如此大的流量增加似乎为这是一个黑洞瞬变的观点提供了支持。X射线光谱拟合的吸收功率法产生非物理光子指数，而最佳拟合的吸收盘黑体模型的参数是典型的吸积~10 Msol黑洞在热占主导地位的状态。
英文摘要：
We report the discovery of a bright X-ray transient, CXOU J132527.6-430023, in the nearby early-type galaxy NGC 5128. The source was first detected over the course of five Chandra observations in 2007, reaching an unabsorbed outburst luminosity of 1-2*10^38 erg/s in the 0.5-7.0 keV band before returning to quiescence. Such luminosities are possible for both stellar-mass black hole and neutron star X-ray binary transients. Here, we attempt to characterize the nature of the compact object. No counterpart has been detected in the optical or radio sky, but the proximity of the source to the dust lanes allows for the possibility of an obscured companion. The brightness of the source after a >100 fold increase in X-ray flux makes it either the first confirmed transient non-ULX black hole system in outburst to be subject to detailed spectral modeling outside the Local Group, or a bright (>10^38 erg/s) transient neutron star X-ray binary, which are very rare. Such a large increase in flux would appear to lend weight to the view that this is a black hole transient. X-ray spectral fitting of an absorbed power law yielded unphysical photon indices, while the parameters of the best-fit absorbed disc blackbody model are typical of an accreting ~10 Msol black hole in the thermally dominant state.
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