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arXiv 2106.14909astro-ph.HEastro-ph.SR
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O型施主星内禀X射线辐射和超巨星快X射线瞬变最暗态的残余吸积

Detecting the intrinsic X-ray emission from the O-type donor star and the residual accretion in a Supergiant Fast X-ray Transient during its faintest state

L. Sidoli, K. Postnov, L. Oskinova, P. Esposito, A. De Luca, M. Marelli, R. Salvaterra

摘要:

我们报告了2020年6月对超巨星快速X射线瞬变(SFXT)IGR J 08408 -4503进行的XMM-牛顿观测的结果。该源由一个围绕O 8.5Ib-II(f)p星LM Vel运行的致密天体(可能是一颗中子星)组成。X射线光变曲线显示出非常低的发射水平,被单个微弱的耀斑打断。对耀斑期间和平静期间测得的光谱进行了分析。静态显示连续谱以及去卷积到三个光谱模型:两个组件是从碰撞电离等离子体(与温度kT 1 =0.24千电子伏和kT 2 =0.76千电子伏),连同幂律模型(光子指数为2.55),占主导地位的2千电子伏以上。在这个最低水平发射的X射线通量为3.2 $\times10^{-13}$ erg/cm 2/s(0.5-10 keV,校正星际吸收),这意味着X射线光度为1.85 $\times10^{32}$ erg/s(2.2 kpc)。两个温度的碰撞电离等离子体是固有的施主恒星的恒星风,而幂律可以解释为由于剩余的,低层次的吸积到紧凑的对象的排放。在最低状态下,仅由幂律分量贡献的X射线光度为(4.8 $\pm{1.4})\times10^{31}$ erg/s,这是从SFXT中的致密物体检测到的最低静态光度。由于XMM-牛顿捕捉到了这种非常微弱的X射线状态,施主恒星LM Vel风中的X射线发射可以首次得到很好的证实和详细的研究,以及对致密物体的非常低的吸积。IGR J 08408 -4503中致密天体上的剩余吸积率可以解释为在准球形辐射驱动的沉降吸积阶段,从超巨星施主风以低Bondi捕获率进入中子星磁层的(可能磁化的)等离子体的玻姆扩散。

英文摘要:

We report on the results of an XMM-Newton observation of the Supergiant Fast X-ray Transient (SFXT) IGR J08408-4503 performed in June 2020. The source is composed by a compact object (likely a neutron star) orbiting around an O8.5Ib-II(f)p star, LM Vel. The X-ray light curve shows a very low level of emission, punctuated by a single, faint flare. Analysis of spectra measured during the flare and during quiescence is performed. The quiescent state shows a continuum spectrum well deconvolved to three spectral models: two components are from a collisionally-ionized plasma (with temperatures kT1=0.24 keV and kT2=0.76 keV), together with a power law model (photon index of 2.55), dominating above 2 keV. The X-ray flux emitted at this lowest level is 3.2$\times10^{-13}$ erg/cm2/s (0.5-10 keV, corrected for the interstellar absorption), implying an X-ray luminosity of 1.85$\times10^{32}$ erg/s (at 2.2 kpc). The two temperature collisionally-ionized plasma is intrinsic to the stellar wind of the donor star, while the power law can be interpreted as emission due to residual, low level accretion onto the compact object. The X-ray luminosity contributed by the power law component only, in the lowest state, is (4.8$\pm{1.4})\times10^{31}$ erg/s, the lowest quiescent luminosity detected from the compact object in an SFXT. Thanks to this very faint X-ray state caught by XMM-Newton, X-ray emission from the wind of the donor star LM Vel could be well-established and studied in detail for the first time, as well as a very low level of accretion onto the compact object. The residual accretion rate onto the compact object in IGR J08408-4503 can be interpreted as the Bohm diffusion of (possibly magnetized) plasma entering the neutron star magnetosphere at low Bondi capture rates from the supergiant donor wind at the quasi-spherical radiation-driven settling accretion stage.

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