M87射流中HST-1的类核性质
The Core-like Nature of HST-1 in the M87 Jet
摘要：
我们调查的总通量密度，光谱，偏振和法拉第旋转变化的HST-1在M87喷流在2003年至2007年的爆发期间，通过多历元VLA观测在8，15和22 GHz。与一般耀变体的情况相反，HST-1的流量密度在较低的频率从无线电到X射线的上升较早，并且随着爆发的增长，光谱正在软化，这表明HST-1内新出现的子成分具有相对陡峭的光谱。特别是，内在的EVPA单调变化的$\sim90^\circ$在3个波段的期间，和所有的，但在东端的静止子组件的HST-1的超光速偏离偏离整体射流方向向下游移动，与最外的子组件的运动从一侧的射流轴弯曲到另一侧。这些强有力地证明了HST-1周围存在螺旋磁场，这也得到了子成分可能在该区域加速的事实的支持。在上升阶段，分数极化相对较低，而在衰减阶段，三个波段的极化水平几乎相当。鉴于相当大的RM值，法拉第旋转预计将主要发生在HST-1的外部，在衰变阶段，这是很好地支持了HST-1周围的扩散发射的存在，并与RM下降的情况下，随着时间的推移变得缓慢。
英文摘要：
We investigate the total flux density, spectral, polarization, and Faraday rotation variability of HST-1 in the M87 jet during the outburst from 2003 to 2007 through multi-epoch VLA observations at 8, 15, and 22 GHz. Contrary to the general case for blazars, the flux densities of HST-1 rise earlier at lower frequencies from radio to X-ray, and the spectra are softening with the growth of outburst, indicating that the newly emerging subcomponents within HST-1 have relatively steep spectra. In particular, the intrinsic EVPA varies monotonically by $\sim90^\circ$ at the 3 wavebands during the period, and all but the stationary subcomponent in the eastern end of HST-1 move downstream superluminally deviating divergently from the overall jet direction, with the motion of the outmost subcomponent bending from one side of the jet axis to another. These strongly argue for the presence of helical magnetic fields around HST-1, which is also supported by the fact that the subcomponents might be accelerated in this region. The fractional polarization is relatively low in the rising stage, and in the decaying stage the polarization levels are almost comparable at the 3 wavebands. In view of the quite large RM values, Faraday rotation is expected to occur dominantly external to HST-1 in the decaying stage, which is well supported by the presence of diffuse emission around HST-1, and consistent with the scenario that RM decrease gets slower with time.
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