New XMM-Newton Analysis of Three Bright X-Ray Sources in M31 Globular Clusters, Including a New Black Hole Candidate
New XMM-Newton Analysis of Three Bright X-Ray Sources in M31 Globular Clusters, Including a New Black Hole Candidate
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对 M31 球状星团中三个明亮 X 射线源（包括一个新黑洞候选者）的新 XMM-牛顿分析
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发表时间：
2008
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通讯作者：
G. Sala
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作者：
Robin Barnard;H. Stiele;D. Hatzidimitriou;A. Kong;B. Williams;W. Pietsch;U. Kolb;F. Haberl;G. Sala
我们对 M31 的 XMM-牛顿扩展巡天中的三个球状星团 X 射线源进行了详细分析。 2006 年 12 月 26 日，用 XMM-Newton 观测到 M31 球状星团 Bo 45 (XBo 45) 的 X 射线对应物。它的组合 pn+MOS 0.3-10 keV 光曲线变化约 10%，并且它的 0.3-7.0 keV 发射光谱可以通过光子指数 1.44 ± 0.12 的吸收功率定律很好地描述。无论吸积体是中子星还是黑洞，其变异性和发射都是低硬态低质量 X 射线双星 (LMXB) 的特征。这种行为通常在光度≲10% Eddington 时观察到。然而，XBo 45 在未吸收的 0.3-10 keV 光度为 2.5 ± 0.2 × 1038 erg s−1 时表现出这种行为，对于吸积氢的 1.4 M☉ 中子星来说，光度约为 140% 爱丁顿。因此，我们将 XBo 45 确定为新的候选黑洞 LMXB。 XBo 45 似乎在大约 30 年内一直保持明亮，这与通过潮汐捕获形成的球状星团黑洞双星的理论预测一致。 Bo 375 是在 2007 年 1 月 2 日的 XMM-牛顿观测中观测到的，它具有典型的明亮中子星 LMXB 的双分量光谱。 Bo 135 与 Bo 45 在同一区域被观测到，并且可能包含黑洞或中子星。
We present a detailed analysis of three globular cluster X-ray sources in the XMM-Newton extended survey of M31. The X-ray counterpart to the M31 globular cluster Bo 45 (XBo 45) was observed with XMM-Newton on 2006 December 26. Its combined pn+MOS 0.3-10 keV light curve was seen to vary by ~10%, and its 0.3-7.0 keV emission spectrum was well described by an absorbed power law with photon index 1.44 ± 0.12. Its variability and emission is characteristic of low-mass X-ray binaries (LMXBs) in the low-hard state, whether the accretor is a neutron star or black hole. Such behavior is typically observed at luminosities ≲10% Eddington. However, XBo 45 exhibited this behavior at an unabsorbed, 0.3-10 keV luminosity of 2.5 ± 0.2 × 1038 erg s−1, or ~140% Eddington for a 1.4 M☉ neutron star accreting hydrogen. Hence, we identify XBo 45 as a new candidate black hole LMXB. XBo 45 appears to have been consistently bright for ~30 years, consistent with theoretical prediction for a globular cluster black hole binary formed via tidal capture. Bo 375 was observed in the 2007 January 2 XMM-Newton observation, and has a two-component spectrum that is typical for a bright neutron star LMXB. Bo 135 was observed in the same field as Bo 45, and could contain either a black hole or a neutron star.