黑洞X射线双星磁场输运和喷流
Transfer of Magnetic Field and Jets in Black Hole X-Ray Binaries
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摘要: 黑洞X射线双星(Black Hole X-Ray Binary, BHXRB)是由中心致密黑洞与其伴星组成的双星系统. 其在爆发阶段总是伴随着多波段的辐射. 随着多波段天文领域的发展, 目前对于其多波段辐射背后的物理过程及能谱分布(spectral energy distribution, SED)已有大致图像: 黑洞周围的吸积盘与冕主导X射线辐射; 黑洞X射线双星总是伴随着喷流, 喷流为射电波段辐射的主要来源; 主导光学/近红外波段辐射的物理过程较为复杂, 一般认为有X射线再辐射、外吸积盘粘滞热辐射和喷流发射3个物理过程. 研究发现各波段辐射光度间往往存在幂律相关性. 这暗示了各波段辐射背后物理过程存在关联. 然而, 喷流与吸积盘之间关联的具体物理过程仍不明确. 研究表明BHXRB中外部弱磁场可以通过吸积盘向内径移形成吸积盘内的强磁场. 这一过程使得吸积盘内部磁场被大幅增强, 这为理论研究上解释喷流产生及加速的BZ (Blandford-Znajek)模型与BP (Blandford-Payne)模型提供了先决条件. 同时强磁场也会改变内部吸积流的结构, 可能在靠近黑洞区域形成磁囚禁吸积盘(magnetic arrested accretion disk, MAD). 借助慧眼卫星(Insight Hard X-ray Modulation Telescope, Insight-HXMT)的宽能段X射线观测, 得以窥见如此致密区域中的高能辐射过程. 考虑黑洞双星中的磁场输运过程, 可以一定程度上解释吸积盘-喷流耦合关系. 回顾了近年来对BHXRB吸积磁场输运及喷流的研究, 并介绍了黑洞吸积与磁场输运的最新进展.Abstract: Black hole X-ray binary (BHXRB) is a binary system consisting of a central compact black hole and its companion star. Its outburst phase is always accompanied by multi-wavelength emission. With the development of the multi-messenger astronomy, a general picture of the physical processes and spectral energy distribution (SED) behind the multi-wavelength radiation has been formed. The accretion disk and corona around the black hole dominate the X-ray emission; black hole X-ray binaries are always accompanied by jets, and the jets are the main source of radio emission; the physical process that dominates the optical/near-infrared emission is more complicated. It is generally believed that there are three physical processes involved, including X-ray reprocessing, viscous thermal radiation from the outer accretion disc, and jet emission. Many researches indicate that there is often a clear power-law correlation between the flux of the multi-wavelength emissions. This implies a correlation between the physical processes behind the multi-wavelength emissions. However, the specific physical processes underlying the association between the jet and the accretion disc remain unclear. It has been suggested that the weak external magnetic field in the BHXRB can be radially dragged inwards by the accretion disc to form a strong magnetic field near the black hole. This process results in a significant amplification of the magnetic field in the accretion flow. And it is a prerequisite for theoretical studies of the BZ (Blandford-Znajek) model and the BP (Blandford-Znajek) model for jet launching and acceleration. Also, the strong magnetic fields can change the structure of the internal accretion flow, possibly forming the magnetically arrested accretion disks (MADs) in regions close to the black hole. Using the broad band X-ray observations from Insight-HXMT (Insight Hard X-ray Modulation Telescope), we are able to glimpse the high-energy radiation processes occurring in such densely compact regions. The transfer of magnetic fields in BHXRBs may provide insights into, or partially explain, the coupling between the accretion disk and the jet. We will review the researches on BHXRB accretion magnetic field advection and jets over the decades, and introduce the recent research on black hole accretion and magnetic field advection.