由VLA低频电离层与暂现实验发现的一个致密对称天体
A Compact Symmetric Object Discovered by the VLA Low-band Ionosphere and Transient Experiment
AI总结：
本研究利用VLITE的低频数据发现致密对称天体J0330-2730，通过VLBA成像揭示其双瓣结构，分析其光变机制并探讨其偏离标准喷流模型的可能原因，展现了VLITE识别年轻致密射电源的潜力。
摘要：
我们展示了对一个兆赫兹峰值谱（MPS）源的甚长基线阵列（VLBA）新成像结果，该源是利用卡尔·G·央斯基甚大阵（VLA）的共生低频数据发现的。该源J0330-2730是在VLA低频电离层与暂现实验（VLITE）的多历元数据中被识别出的，VLITE会在VLA的常规观测期间持续采集340 MHz的低频数据。我们对VLITE光变曲线的分析表明，J0330-2730在约一年的时标上存在显著的340 MHz流量变化，变化幅度约为20%。我们的VLBA图像揭示出它具有可分辨的双瓣形态，投影线尺度为64秒差距。我们探讨了能够解释观测到的340 MHz光变以及该源毫角秒尺度性质的合理机制，排除了可变多普勒增亮的可能，得出星际折射闪烁或可变自由-自由吸收是最可能的解释。我们认为J0330-2730的性质与致密对称天体（CSOs）类别相符，并探讨了该源的演化阶段。VLBA揭示的可分辨瓣的延展尺度，远小于基于标准同步辐射自吸收喷流模型的转折频率-尺度关系的预测值。我们讨论了这种偏离转折频率-尺度关系的可能解释，包括由潮汐瓦解事件这类暂现现象形成的喷流，或是被稠密气体或高压环境阻碍的“受阻喷流”。本研究凸显了VLITE在识别致密、年轻射电源方面的潜力。
英文摘要：
We present new Very Long Baseline Array (VLBA) imaging of a MHz-peaked spectrum (MPS) source that was found using commensal low-frequency data taken with the Karl G. Jansky Very Large Array (VLA). The source, J0330-2730, was identified in multi-epoch data from the VLA Low-band Ionosphere and Transient Experiment (VLITE). VLITE continuously collects low-frequency data at 340 MHz during regular VLA observations. Our analysis of the VLITE light curve demonstrates that J0330-2730 has significant 340 MHz flux variability at the ~20% level over a timescale of approximately one year. Our VLBA images reveal a resolved, double-lobed morphology with a projected linear size of 64 pc. We consider plausible mechanisms that could explain the observed 340 MHz variability and the source properties on milliarcsecond scales. We rule-out variable Doppler boosting and conclude that refractive interstellar scintillation or variable free-free absorption are the most likely explanations. We argue that the properties of J0330-2730 are consistent with the class of compact symmetric objects (CSOs) and consider the evolutionary stage of the source. The extent of the resolved lobes revealed by the VLBA is significantly smaller than predictions based on the turnover-size relation for a standard synchrotron self-absorbed jet model. We discuss possible explanations for the departure from the turnover-size relation, including jet formation by a transient phenomenon such as a tidal disruption event or a "frustrated jet" impeded by the presence of dense gas or a high-pressure environment. This study highlights the potential of VLITE for the identification of compact and young radio sources.
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