Hercules A (Her A) is one of a rare class of dying and transition-type objects, which has a pair of giant, powerful radio lobes and a weak radio core. We reduce and analyze the radio data of Her A that observed by the Expanded Very Large Array (EVLA) during 2010-2011 at C band. The intensity distribution is very smooth along the edge of the lobe front and the intensity also sharply decreases at the edge, which supports that magnetic fields may play an important role in radio lobes. The spectrum of the weak core is very steep and the core flux becomes weaker for about ten percent when compared to that was observed twenty years ago, which suggest that the central engine is still dying quickly. Her A deviates a lot from the relation between [O III] luminosity and low-frequency 178 MHz luminosity (LO III − L178MHz) as defined by other FR I/II sources. However, when only radio core emission is considered, it roughly follows LO III − L178MHz correlation. This result supports that the black-hole accretion and the large-scale jet in Her A are not evolved simultaneously, and indicates that although the large-scale jet is still powerful while the accretion and the inner jet are changed into an inactive state. Based on the estimated Bondi accretion rate, we model the spectrum of Her A with a radiatively inefficient accretion flow and jet model.

中文翻译：

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赫拉克勒斯 A 强大射电星系中垂死的吸积物和喷流

赫拉克勒斯A（Her A）是一类罕见的垂死过渡型天体，它有一对巨大而强大的射电瓣和一个微弱的射电核心。我们减少并分析了扩展甚大阵列 (EVLA) 在 2010-2011 年在 C 波段观测到的 Her A 的无线电数据。沿波瓣前沿边缘的强度分布非常平滑，边缘处的强度也急剧下降，这支持磁场可能在无线电波瓣中起重要作用。与二十年前观察到的情况相比，弱核心的频谱非常陡峭，核心通量变弱了大约百分之十，这表明中央引擎仍在快速死亡。Her A 与其他 FR I/II 源定义的 [O III] 光度和低频 178 MHz 光度（LO III - L178MHz）之间的关系有很大偏差。然而，当仅考虑无线电核心发射时，它大致遵循 LO III - L178MHz 相关性。这一结果支持了黑洞吸积和Her A中的大尺度喷流不是同时演化的，表明虽然大尺度喷流仍然强大，但吸积和内部喷流变成了非活动状态。基于估计的邦迪吸积率，我们使用辐射效率低下的吸积流和射流模型对 Her A 的光谱进行建模。