The resolved jet of 3C 273 at 150 MHz Sub-arcsecond imaging with the LOFAR international baselines
The resolved jet of 3C 273 at 150 MHz Sub-arcsecond imaging with the LOFAR international baselines
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3C 273 在 150 MHz 下的解析射流 亚弧秒成像与 LOFAR 国际基线
DOI：
10.1051/0004-6361/202141579
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发表时间：
2022
影响因子：
6.5
通讯作者：
Harwood J
中科院分区：
文献类型：
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作者：
Harwood J
自1963年发现以来，3C 273已经成为研究最广泛的类星体之一，其研究跨越了电磁波谱。因此，虽然对这个历史上著名的来源已经发现了很多，但对它的低频发射却知之甚少。传统上，兆赫兹（MHz）波段的观测缺乏探索小尺度结构所需的分辨率，如结和漫射喷射发射，这对于理解导致观测到的发射的过程至关重要。LOFAR国际基线数据处理方面的进展现在已经消除了这一限制，首次为探索这一关键领域提供了机会。本文利用3C 273在MHz频率下的第一次亚弧秒图像，研究了致密射流结构的形态和产生观测光谱的过程。我们确定了射流的动能，对射流的总体速度和倾斜角进行了限制，并在150兆赫兹寻找难以捉摸的反射流的证据。方法利用LOFAR国际台站（德国、波兰、法国、英国、瑞典）的全补数据，在150 MHz频率下生成3C 273的0.31 × 0.21 arcsec图像。利用千兆赫频率的辅助数据，我们将自由-自由吸收（FFA）和同步加速器自吸收（SSA）模型拟合到每个区域，以确定它们在解释观测光谱方面的有效性。结果所展示的图像首次表明，利用LOFAR国际基线对低赤纬复杂源进行稳健的高保真成像是可能的。我们表明，3C 273的主要小尺度结构与在更高频率下看到的结构相匹配，并对外瓣的延伸进行了微弱的检测。我们发现FFA和SSA模型能够描述结的光谱，而区分模型类型需要进一步的观测，我们得出结论，吸收存在于观测到的发射中。我们确定射流的动能在3.5 × 1043-1.5 × 1044erg s−1之间，这与使用更高频率观测得到的估计一致。我们推导出体积速度和洛伦兹因子的下限分别为β≥0.55和Γ≥1.2。在150 MHz时，反喷流仍然未被检测到，这限制了scj_150 < 40 mJy波束−1的峰值亮度。
ContextSince its discovery in 1963, 3C 273 has become one of the most widely studied quasars with investigations spanning the electromagnetic spectrum. While much has therefore been discovered about this historically notable source, its low-frequency emission is far less well understood. Observations in the megahertz (MHz) regime have traditionally lacked the resolution required to explore small-scale structures, such as knots and diffuse jet emission, that are crucial to understanding the processes that result in the observed emission. Advances in the processing of LOFAR international baseline data have now removed this limitation, providing the opportunity to explore this key area for the first time.AimsIn this paper we use the first sub-arcsecond images of 3C 273 at MHz frequencies to investigate the morphology of the compact jet structures and the processes that result in the observed spectrum. We determine the jet’s kinetic power, place constraints on the bulk speed and inclination angle of the jets, and look for evidence of the elusive counterjet at 150 MHz.MethodsUsing the full complement of the LOFAR international stations (German, Poland, France, UK, Sweden), we produce 0.31 × 0.21 arcsec images of 3C 273 at 150 MHz. Using ancillary data at gigahertz frequencies, we fit free-free absorption (FFA) and synchrotron self-absorption (SSA) models to each region in order to determine their validity in explaining the observed spectra.ResultsThe images presented display for the first time that robust high-fidelity imaging of low-declination complex sources is now possible with the LOFAR international baselines. We show that the main small-scale structures of 3C 273 match those seen at higher frequencies, with a tenuous detection of an extension to the outer lobe. We find that FFA and SSA models are able to describe the spectrum of the knots and, while differentiating between model types requires further observations, we conclude that absorption is present in the observed emission. We determine the kinetic power of the jet to be in the range of 3.5 × 1043–1.5 × 1044erg s−1, which agrees with estimates made using higher frequency observations. We derive lower limits for the bulk speed and Lorentz factor ofβ≳ 0.55 and Γ ≥ 1.2, respectively. The counterjet remains undetected at 150 MHz, placing a limit on the peak brightness ofScj_150< 40 mJy beam−1.