VAPOLA——利用ALMA开展的AGNs与Sgr A*的多年多波段偏振巡天 II. 2017至2023年的偏振光谱特性及其演化
VAPOLA - A multiyear, multiband polarization survey of AGNs and Sgr A* at millimeter wavelengths with ALMA II. Spectropolarimetric properties and their evolution from 2017 to 2023
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中文总结 AI 辅助
本研究利用ALMA对39个AGNs及Sgr A*开展2017-2023年的VLBI偏振光谱分析，揭示其偏振特性的时间变异性及RM随频率变化的规律，探讨法拉第旋转的可能起源。
中文摘要 AI 辅助
我们对2017年至2023年间5次甚长基线干涉测量（VLBI）观测 campaign中，用阿塔卡马大型毫米波/亚毫米波阵列（ALMA）观测得到的39个活动星系核（AGNs）样本及人马座A*（Sagittarius A*）的偏振光谱特性开展了系统分析。我们在总强度和偏振层面表征了致密核，重点关注线性偏振度（LP）、电矢量位置角（EVPA）和法拉第旋转量（RM）在时间和光谱域的变化行为。我们既研究了M87、Sgr A*、3C273、3C279等单个天体，也分析了平谱射电类星体、蝎虎座BL型天体（BLLac objects）及其他活动星系等不同源类的整体特性。总强度和光谱指数在周时间尺度上通常保持稳定，而偏振特性常表现出强变异性，LP、EVPA和RM会在日尺度上发生显著变化。多个源显示出大的EVPA旋转，同时伴随LP和RM的变化，部分情况与耀发活动重合。对于拥有可靠多波段测量数据的所有源，我们观测到RM的幅度随观测频率升高而增大，这与相对论性喷流周围磁化鞘层产生的法拉第旋转一致，但无法排除吸积流（尤其对于Sgr A*）作为起源的可能性。
英文摘要
We present a systematic analysis of the spectropolarimetric properties of a sample of 39 active galactic nuclei and Sagittarius A* observed with the Atacama Large Millimeter/submillimeter Array during five VLBI campaigns between 2017 and 2023. We characterize the compact cores in total intensity and polarization, focusing on the behavior or the linear polarization fraction (LP), electric vector position angle (EVPA), and Faraday rotation measure (RM) over time and spectral domains. We investigate both individual objects--such as M87, Sgr A*, 3C273, and 3C279--and ensemble properties of different source classes, including flat-spectrum radio quasars, BLLac objects, and other active galaxies. While total intensity and spectral index are generally stable on weekly timescales, polarization properties often exhibit strong variability, with significant day-to-day changes in LP, EVPA, and RM. Several sources display large EVPA rotations accompanied by variations in LP and RM, in some cases coinciding with flaring activity. We observe that the magnitude of RM increases with observing frequency for all sources for which we have reliable multi-band measurements, consistent with Faraday rotation arising in a magnetized sheath surrounding the relativistic jet, although an origin in the accretion flow--particularly in the case of Sgr A*--cannot be ruled out.
