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arXiv 1404.0901astro-ph.HE
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第一个Be/黑洞系统X射线辐射的发现

Discovery of X-ray emission from the first Be/black hole system

P. Munar-Adrover, J. M. Paredes, M. Ribó, K. Iwasawa, V. Zabalza, J. Casares

摘要:

MWC 656(= HD 215227)是最近发现的第一个由Be星和黑洞(BH)组成的双星系统。我们用\textit{XMM-Newton}对它进行了观测,发现了一个与光学星位置一致的微弱X射线源,从而证明它是第一个Be/BH X射线双星。光谱分析需要一个模型拟合两个组件,一个黑体加一个幂律,与$k_{\rm B}T = 0.07^{+0.04}_{-0.03}$ ~keV和光子指数$Γ= 1.0\pm0.8$,分别。非热分量占主导地位以上$\simeq$ 0.8千电子伏。所获得的总通量为$F(0.3$ - $5.5~{\rm keV}) = (4.6^{+1.3}_{-1.1})\times10^{-14}$ erg cm $^{-2}$ s $^{-1}$。在$2.6\pm0.6$ ~kpc的距离处,总通量转化为光度$L_{\rm X} = (3.7\pm1.7)\times10^{31}$ erg s $^{-1}$。考虑到黑洞质量的估计范围为3.8- 6.9 $M_{\odot}$,这个光度代表了$(6.7\pm4.4)\times10^{-8}~L_{\rm Edd}$,这是典型的恒星质量黑洞的静止。我们讨论了两个光谱分量的起源:热分量是与热的风的Be星,而幂律分量是与从BH附近的排放。我们还发现MWC~656在射电-X射线光度图中的位置可能与BH低质量X射线双星中观测到的射电/X射线关联相一致。这表明,这种相关性也可能是有效的BH高质量X射线双星(HMXB)与X射线亮度下降到$\sim10^{-8} L_{\rm Edd}$。MWC~656可以用来研究BH~ HMXB的吸积过程和吸积/抛射耦合。

英文摘要:

MWC 656 (= HD 215227) was recently discovered to be the first binary system composed of a Be star and a black hole (BH). We observed it with \textit{XMM-Newton}, and detected a faint X-ray source compatible with the position of the optical star, thus proving it to be the first Be/BH X-ray binary. The spectrum analysis requires a model fit with two components, a black body plus a power law, with $k_{\rm B}T = 0.07^{+0.04}_{-0.03}$~keV and a photon index $Γ= 1.0\pm0.8$, respectively. The non-thermal component dominates above $\simeq$0.8 keV. The obtained total flux is $F(0.3$--$5.5~{\rm keV}) = (4.6^{+1.3}_{-1.1})\times10^{-14}$ erg cm$^{-2}$ s$^{-1}$. At a distance of $2.6\pm0.6$~kpc the total flux translates into a luminosity $L_{\rm X} = (3.7\pm1.7)\times10^{31}$ erg s$^{-1}$. Considering the estimated range of BH masses to be 3.8--6.9 $M_{\odot}$, this luminosity represents $(6.7\pm4.4)\times10^{-8}~L_{\rm Edd}$, which is typical of stellar-mass BHs in quiescence. We discuss the origin of the two spectral components: the thermal component is associated with the hot wind of the Be star, whereas the power law component is associated with emission from the vicinity of the BH. We also find that the position of MWC~656 in the radio versus X-ray luminosity diagram may be consistent with the radio/X-ray correlation observed in BH low-mass X-ray binaries. This suggests that this correlation might also be valid for BH high-mass X-ray binaries (HMXBs) with X-ray luminosities down to $\sim10^{-8} L_{\rm Edd}$. MWC~656 will allow the accretion processes and the accretion/ejection coupling at very low luminosities for BH~HMXBs to be studied.

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