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arXiv 1104.0860astro-ph.HE
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用Chandra和XMM-Newton在M31球状星团中发现了四个新的黑洞候选者

Four new black hole candidates identified in M31 globular clusters with Chandra and XMM-Newton

R. Barnard, M. Garcia, Z. Li, F. Primini, S. S. Murray

摘要:

利用123个Chandra和4个XMM-Newton对M31中心区域的观测,我们在M31球状星团中发现了4个新的黑洞候选者。与Bo 163(XB 163)相关的X射线源是一个周期性的瞬变,最高光度约为1.4 E +38 erg/s,比任何来自中子星瞬变Aql X-1或4U 1608 - 452的爆发都要亮得多;爆发显然比观测到的峰值早45天,因此光度可能要高得多。我们通过观测亮度超过中子星双星阈值的"低态"发射光谱,将XB 082、XB 153和XB 185确定为BHC。这些是向我们发射各向异性辐射的中子星系统的概率<4E-4,它们的变化表明辐射来自单一来源。因此,我们得出结论,这些系统可能包含黑洞而不是中子星。我们现在已经在该区域确定了4个持续明亮的BHC;它们都是背景AGN的概率<1E-20。根据理论,捐赠者可能是潮汐捕获的主序星,或者是超紧凑双星中的白矮星。我们发现,特别是质量大(XB 082)或金属丰富(XB 144)的GC可以托管明亮的X射线源,除了那些都是(XB 163)。我们的方法可以揭示BHC在其他明亮的X射线源。

英文摘要:

We have identified four new black hole candidates in M31 globular clusters using 123 Chandra, and 4 XMM-Newton observations of the M31 central region. The X-ray source associated with Bo 163 (XB163) is a recurrent transient, with the highest luminosity ~1.4E+38 erg/s, considerably brighter than any outbursts from the neutron star transients Aql X-1 or 4U 1608-452; the outburst apparently started ~45 days earlier than the observed peak, hence the luminosity could have been considerably higher. We identified XB082, XB153 and XB185 as BHCs by observing "low state" emission spectra at luminosities that exceed the threshold for neutron star binaries. The probability that these are neutron star systems with anisotropic emission beamed toward us is <4E-4, and their variability suggests emission from a single source. We therefore conclude that these systems likely contain black holes rather than neutron stars. We have now identified 4 persistently bright BHCs in the region; the probability that these are all background AGN is <1E-20. According to theory, the donors could be tidally captured main sequence stars, or white dwarves in ultra-compact binaries. We find that GCs that are particularly massive (XB082) or metal rich (XB144) can host bright X-ray sources in addition to those that are both (XB163). Our method may reveal BHCs in other bright X-ray sources.

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