发表机构
National Centre for Radio Astrophysics - Tata Institute of Fundamental Research; University of Pretoria; Inter-University Institute for Data Intensive Astronomy（国家射电天体物理中心-塔塔基础研究所; 比勒陀利亚大学; 跨大学数据密集型天文学研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究利用uGMRT对射电宁静赛弗特星系NGC 4235开展多频偏振观测，首次在低频段约束其旋转量，估算出相关磁化等离子体参数，拓展了法拉第旋转诊断在低功率射电宁静AGN领域的应用。
AI 中文摘要
我们利用升级后的巨米波射电望远镜（uGMRT）对射电宁静赛弗特星系NGC 4235开展多频偏振研究，旨在约束其千秒差距尺度射电辐射的法拉第旋转特性。这是首次利用uGMRT的两个频段进行偏振分析，也是首次对弱射电源（1.3 GHz处流量密度为17.1±1.7 mJy，663 MHz处为27.7±2.8 mJy）在低频段的旋转量（RM）进行约束。我们探测到与NGC 4235的“核”及延展瓣相关的线性偏振射电辐射。宽带偏振分析得出“核”处的RM值约为200 rad m⁻²，表明同步辐射区域外的磁化等离子体产生了法拉第旋转。利用这些RM约束，我们估算出法拉第旋转介质的平均电子密度约为3×10⁻² cm⁻³，对应的特征扰动尺度约为0.3秒差距，假设磁化区域大小约为1.3千秒差距，这与弥散磁化鞘或AGN驱动风的模型一致。这些结果将经典法拉第旋转诊断扩展到低功率射电宁静AGN领域，证明了uGMRT宽带偏振测量在探测此类AGN内部及周围磁化环境中的潜力。
英文摘要
We present a multi-frequency polarimetric study of the radio-quiet Seyfert galaxy NGC 4235 using the upgraded Giant Metrewave Radio Telescope (uGMRT), aimed at constraining the Faraday rotation properties of its kpc-scale radio emission. This marks the first-ever analysis of polarization across two frequency bands of the uGMRT and the first constraints on rotation measure (RM) at lower frequencies for a weak radio source (17.1$\pm$1.7 mJy at 1.3 GHz, 27.7$\pm$2.8 mJy at 663 MHz). We detect linearly polarized radio emission associated with the `core' and the extended lobes of NGC 4235. Broadband polarimetric analysis yields an RM value of {$\sim200$ rad m$^{-2}$} in the `core', indicating Faraday rotation by magnetized plasma external to the synchrotron-emitting regions. Using these RM constraints, we estimate an average electron density of the Faraday-rotating medium of $\sim$3$\times10^{-2}$ cm$^{-3}$ for a characteristic perturbation scale of $\sim$0.3 parsec within an assumed magnetized region of size $\sim$1.3 kpc, consistent with a diffuse magnetized sheath or AGN-driven wind. These results extend classical Faraday rotation diagnostics to the low-power, radio-quiet AGN regime and demonstrate the potential of uGMRT broadband polarimetry for probing magnetized environments in and around such AGN.
CommentsAccepted for publication in the Journal of Astrophysics and Astronomy
