ASKAP变源与慢瞬变巡天观测到的活动星系核射电光度的年际-十年际变化
Year-timescale changes in AGN radio luminosity as seen by the ASKAP Variables and Slow Transients Survey
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中文总结 AI 辅助
ASKAP VAST巡天发现64972个非耀变体AGN中的101个致密射电源存在年际-十年际射电光度变化，揭示了部分源的射电噪转变源于年轻喷流，且射电噪状态多为暂时现象。
中文摘要 AI 辅助
数十个此前射电宁静的活动星系核（AGN）被观测到在10年以上的时标内于1-3 GHz频率下转变为射电噪，这被解释为新喷流启动所致。我们从澳大利亚SKA路径finder变源与慢瞬变巡天（ASKAP VAST）的64972个非耀变体AGN样本中，识别出101个致密射电源，它们在1-6年的时标内887.5 MHz频段的流量密度增幅达80%-1800%。我们利用新观测和存档巡天数据获取了光学光谱与射电光谱能量分布（SED），判定其中60个源的变化符合星际折射闪烁导致的外禀变异性，41个源的变化源于内禀原因；26个源持续增亮，2个源从射电宁静转变为射电噪。我们得出结论，持续增亮的AGN是由潮汐瓦解事件或吸积特性变化引发的年轻射电喷流所致，这些源在同期更高频率下无变异性，符合膨胀辐射区的预期。14个源初始具有倒转或峰状SED，之后要么在拐点以下变平，要么演化为陡SED，与年轻膨胀喷流一致；12个源具有无变异性的陡谱或吉赫兹峰状SED，表明其拥有演化更缓慢的喷流。我们对此前发现的启动新喷流的AGN展开研究，发现多个源在多个频率下已变暗，表明观测到的射电噪是暂时的，而非射电活动持续期的开端。
英文摘要
A few dozen previously radio-quiet active galactic nuclei (AGN) have been observed to transition to radio-loud at 1-3 GHz frequencies over timescales of more than a decade, and this has has been interpreted to be due to newly launched jets. We identified 101 compact radio sources out of a sample of 64,972 non-blazar AGN which increased in flux density by 80-1800% over 1-6 years in the 887.5 MHz Australian SKA Pathfinder Variables and Slow Transients survey. We obtained optical spectra and radio SEDs using new observations and archival survey data. We determined 60 sources were consistent with extrinsic variability due to refractive interstellar scintillation and 41 were variable due to intrinsic causes, with 26 continuously brightening and two transitioning from radio-quiet to radio-loud. We concluded that young radio jets launched by either tidal disruption events or changes in the accretion properties were responsible for the continuously brightening AGN. These sources were non-variable at higher frequencies over the same time period, as expected for an expanding emission region. Fourteen sources had inverted or peaked SEDs initially which either flattened below the turnover or evolved into steep SEDs, consistent with young, expanding jets. Twelve sources had non-variable steep or gigahertz-peaked SEDs, which suggested these hosted more slowly evolving jets. We investigated the previously discovered AGN with newly launched jets, and found several have faded at multiple frequencies, which suggested the observed radio-loudness was temporary, rather than the onset of a sustained period of radio activity.
