RadioAstron 空间VLBI成像观测M87喷流：II. 4.8 GHz下的秒差距尺度结构
RadioAstron space-VLBI imaging of the jet in M87: II. The parsec-scale structure at 4.8 GHz
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中文总结 AI 辅助
利用RadioAstron空间VLBI在4.8 GHz对M87喷流成像，揭示螺旋结构源于开尔文-亥姆霍兹不稳定性，并发现谱变平部分为CLEAN成像的系统效应。
中文摘要 AI 辅助
我们展示了2014年2月4日至5日在4.8 GHz（λ=6.2 cm）频率下获得的M87喷流的RadioAstron观测结果。10米空间天线与地面射电望远镜之间的相关信号被探测到，其投影基线长度可达约3个地球直径（0.65 Gλ）。核心下游喷流的取向向北偏移，这与其它研究中报道的长期振荡趋势一致。开尔文-亥姆霍兹不稳定性的椭圆体模态可以产生观测到的喷流螺旋形状。该不稳定性模态的估计波长表明，其起源可能与吸积盘中的某些过程有关。我们展示了1.7-4.8 GHz和4.8-15.4 GHz的谱指数图，显示谱在外侧流线和喷流脊柱方向变平。模拟和分析表明，这种谱变平部分是人为造成的，是VLBI成像中CLEAN程序的一种常见系统效应。M87喷流的谱指数与光学薄发射一致，而其变陡可能由不稳定性模态的传播引起，这些模态在喷流边界附近及其内部产生较高压力区域。
英文摘要
We present RadioAstron observations of the M87 jet obtained on 2014 February 4-5 at 4.8 GHz ($λ=6.2$ cm). The correlated signals between the 10-m space antenna and ground-based radio telescopes were detected up to projected baselines of $\thicksim3$\,Earth diameters (0.65~G$λ$). The orientation of the jet downstream of the core shifts northward, consistent with the long-term oscillating trend reported in other studies. An elliptical body mode of the Kelvin-Helmholtz instability can create the observed helical shape of the jet. The estimated wavelength of this instability mode suggests that its origin may be related to some processes in the accretion disc. We present 1.7 - 4.8 GHz and 4.8 - 15.4 GHz spectral index maps showing flattening of the spectrum along the outer streamlines and along the jet spine. Simulations and analysis show that this spectral flattening is partially artificial and is a common systematic effect of the CLEAN procedure of VLBI imaging. The spectral index of the M87 jet is consistent with the optically thin emission, while its steepening can be produced by the propagation of the instability modes causing higher pressure regions near the jet boundary and in its interior.
发表机构
- Lebedev Physical Institute（列别捷夫物理研究所）
- Aalto University（阿尔托大学）
- Max-Planck-Institut für Radioastronomie（马克斯·普朗克射电天文研究所）
- Moscow Center for Advanced Studies（莫斯科高等研究中心）
- Joint Institute for VLBI ERIC（甚长基线干涉测量联合研究所）
- Delft University of Technology（代尔夫特理工大学）
机构由 AI 辅助整理，请以论文原文为准。
