The nearby radio galaxy Centaurus A belongs to a class of active galaxies that are luminous at radio wavelengths. Most show collimated relativistic outflows known as jets, which extend over hundreds of thousands of parsecs for the most powerful sources. Accretion of matter onto the central supermassive black hole is believed to fuel these jets and power their emission 1 . Synchrotron radiation from relativistic electrons causes the radio emission, and it has been suggested that the X-ray emission from Centaurus A also originates in electron synchrotron processes 2 – 4 . Another possible explanation is inverse Compton scattering with cosmic microwave background (CMB) soft photons 5 – 7 . Synchrotron radiation needs ultrarelativistic electrons (about 50 teraelectronvolts) and, given their short cooling times, requires some continuous re-acceleration mechanism 8 . Inverse Compton scattering, on the other hand, does not require very energetic electrons, but the jets must stay highly relativistic on large scales (exceeding 1 megaparsec). Some recent evidence disfavours inverse Compton-CMB models 9 – 12 , although other work seems to be compatible with them 13 , 14 . In principle, the detection of extended γ-ray emission, which directly probes the presence of ultrarelativistic electrons, could distinguish between these options. At gigaelectronvolt energies there is also an unusual spectral hardening 15 , 16 in Centaurus A that has not yet been explained. Here we report observations of Centaurus A at teraelectronvolt energies that resolve its large-scale jet. We interpret the data as evidence for the acceleration of ultrarelativistic electrons in the jet, and favour the synchrotron explanation for the X-rays. Given that this jet is not exceptional in terms of power, length or speed, it is possible that ultrarelativistic electrons are commonplace in the large-scale jets of radio-loud active galaxies. Observations of the radio galaxy Centaurus A at teraelectronvolt energies resolve its large-scale jet and favour electron synchrotron processes as the source of its X-ray emission.

中文翻译：

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沿半人马座 A 喷射流解析加速度为非常高的能量

附近的射电星系半人马座 A 属于一类在射电波长下发光的活跃星系。大多数显示出被称为喷流的准直相对论流出，对于最强大的源，它延伸超过数十万秒差距。据信，物质在中央超大质量黑洞上的吸积为这些喷流提供燃料并为其排放提供动力 1。来自相对论电子的同步加速器辐射引起无线电发射，有人提出半人马座 A 的 X 射线发射也起源于电子同步加速器过程 2 - 4 。另一种可能的解释是宇宙微波背景 (CMB) 软光子 5 – 7 的逆康普顿散射。同步辐射需要超相对论电子（大约 50 太电子伏特），而且鉴于它们的冷却时间很短，需要一些连续的再加速机制 8。另一方面，逆康普顿散射不需要非常高能的电子，但喷流必须在大尺度（超过 1 兆秒差距）上保持高度相对论。最近的一些证据不赞成逆康普顿-CMB 模型 9-12，尽管其他工作似乎与它们兼容 13、14。原则上，直接探测超相对论电子存在的扩展 γ 射线发射的检测可以区分这些选项。在千兆电子伏特能量下，半人马座 A 中也有一种不寻常的光谱硬化 15 、 16 ，尚未得到解释。在这里，我们报告了半人马座 A 以太电子伏特能量解析其大规模喷流的观测结果。我们将这些数据解释为喷流中超相对论电子加速的证据，并赞成对 X 射线的同步加速器解释。鉴于这种喷流在功率、长度或速度方面并不例外，超相对论电子可能在射电响亮的活跃星系的大规模喷流中很常见。在太电子伏特能量下对射电星系半人马座 A 的观测解决了它的大规模喷流，并有利于电子同步加速器过程作为其 X 射线发射的来源。