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arXiv 2108.10892astro-ph.HE
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通过它们的无线电可变性识别不断变化的喷流

Identifying changing jets through their radio variability

I. Liodakis, T. Hovatta, M. F. Aller, H. D. Aller, M. A. Gurwell, A. Lähteenmäki, M. Tornikoski

摘要:

超大质量黑洞发射高度相对论性的喷流,其速度达到高达$Γ>50$的洛伦兹因子。射流如何加速到如此高的速度,以及它们沿着射流在何处达到终极速度是与它们的结构、发射和耗散机制密切相关的公开问题。沿喷流的聚束因子的变化可能揭示喷流的加速、减速或弯曲。我们的目标是(1)量化在多个射频的相对论效应和(2)研究可能的喷流速度-视角变化在秒差距尺度。我们使用最先进的代码Magnetron来模拟密歇根大学射电天文台和Metsähovi射电天文台在5个频率下的监测计划的光变曲线,这些频率覆盖了61个源在4.8-37~GHz范围内约25年的观测。我们用ALMA、CARMA和SMA在100-340 GHz范围内的高频射电观测补充了我们的数据集。对于每个频率,我们估计多普勒因子,我们使用它来量化沿射流的相对论效应的可能变化。我们的大多数源在其多普勒因子跨频率方面没有显示出任何统计学上的显著差异。这与在秒差距尺度下所预期的锥形喷流中的恒定速度是一致的。然而,我们的分析揭示了17个源,其中相对论性光束的变化作为频率的函数。在大多数情况下,多普勒因子朝向较低频率增加。只有1253-053显示出相反的行为。通过研究它们的喷流特性,我们发现0420-014的喷流可能在4.8-340 GHz范围内弯曲。对于0212+735,喷流可能是抛物线的,并且仍然在4.8-37 GHz范围内加速。我们讨论了在其余来源中发现的趋势的可能解释。

英文摘要:

Supermassive black holes launch highly relativistic jets with velocities reaching Lorentz factors as high as $Γ>50$. How the jets accelerate to such high velocities and where along the jet do they reach terminal velocity are open questions that are tightly linked to their structure, launching and dissipation mechanisms. Changes in the beaming factor along the jets could potentially reveal jet acceleration, deceleration, or bending. We aim to (1) quantify the relativistic effects in multiple radio frequencies and (2) study possible jet velocity--viewing angle variations at parsec scales. We used the state-of-the-art code Magnetron to model light curves from the University of Michigan Radio Observatory and the Metsähovi Radio Observatory's monitoring programs in five frequencies covering about 25 years of observations in the 4.8-37~GHz range for 61 sources. We supplement our data set with high-frequency radio observations in the 100-340~GHz range from ALMA, CARMA, and SMA. For each frequency we estimate the Doppler factor which we use to quantify possible changes in the relativistic effects along the jets. The majority of our sources do not show any statistically significant difference in their Doppler factor across frequencies. This is consistent with constant velocity in a conical jet, as expected at parsec scales. However, our analysis reveals 17 sources where relativistic beaming changes as a function of frequency. In the majority of cases the Doppler factor increases towards lower frequencies. Only 1253-053 shows the opposite behavior. By exploring their jet properties we find that the jet of 0420-014 is likely bent across the 4.8-340~GHz range. For 0212+735 the jet is likely parabolic, and still accelerating in the 4.8-37~GHz range. We discuss possible interpretations for the trends found in the remaining sources.

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