M87 * 新月形图像的方向
Orientation of the crescent image of M 87*
摘要：
由事件视界望远镜（EHT）获得的黑洞（BH）M 87* 的第一幅图像具有从E到WSW位置角延伸的新月形状，而观测到的大尺度喷流方向是WNW。基于BH吸积流的数值模拟的图像表明，平均而言，投影BH自旋轴应定向SSW。我们探索高度简化的玩具模型的几何分布和运动学的克尔度量中的发射区域，进行射线追踪计算相应的图像，并模拟他们的观察EHT计算相应的vibrium和关闭阶段。我们严格假定（1）BH自旋矢量固定在喷流轴上，（2）发射区相对于BH自旋是静止的和对称的，（3）发射率在局域静止系中是各向同性的。从SSE和WSW之间的新月形部门的排放可以很容易地解释在赤道环的圆形或暴跌测地线流量，无论BH自旋的值。在平面对称的极帽与暴跌测地线流的情况下，位于BH后面的帽的主导图像是敏感的发射器的角动量。在我们的模型的限制，我们还没有找到一个可行的解释所观察到的亮度的ESE部门。最有可能的是，ESE“热点”已产生的非稳态局部扰动的内部吸积流。或者，它可能是由局部各向异性的同步辐射率。EHT的多历元和偏振测量结果将是必不可少的，以验证理论上预期的BH自旋与大尺度喷流的对齐。
英文摘要：
The first image of the black hole (BH) M 87* obtained by the Event Horizon Telescope (EHT) has the shape of a crescent extending from the E to WSW position angles, while the observed direction of the large-scale jet is WNW. Images based on numerical simulations of BH accretion flows suggest that on average the projected BH spin axis should be oriented SSW. We explore highly simplified toy models for geometric distribution and kinematics of emitting regions in the Kerr metric, perform ray tracing to calculate the corresponding images, and simulate their observation by the EHT to calculate the corresponding visibilities and closure phases. We strictly assume that (1) the BH spin vector is fixed to the jet axis, (2) the emitting regions are stationary and symmetric with respect to the BH spin, and that (3) the emissivities are isotropic in the local rest frames. Emission from the crescent sector between SSE and WSW can be readily explained in terms of an equatorial ring with either circular or plunging geodesic flows, regardless of the value of BH spin. In the case of plane-symmetric polar caps with plunging geodesic flows, the dominant image of the cap located behind the BH is sensitive to the angular momentum of the emitter. Within the constraints of our model, we have not found a viable explanation for the observed brightness of the ESE sector. Most likely, the ESE "hotspot" has been produced by a non-stationary localised perturbation in the inner accretion flow. Alternatively, it could result from locally anisotropic synchrotron emissivities. Multi-epoch and polarimetric results from the EHT will be essential to verify the theoretically expected alignment of the BH spin with the large-scale jet.
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