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arXiv 1509.01889astro-ph.GAastro-ph.HE
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射电强窄线Seyfert 1星系在秒差距尺度上的射电性质

The Radio Properties of Radio-Loud Narrow-Line Seyfert 1 Galaxies on Parsec Scales

Minfeng Gu, Yongjun Chen, S. Komossa, Weimin Yuan, Zhi-Qiang Shen, Kiyoaki Wajima, Hongyan Zhou, J. A. Zensus

摘要:

我们提出了在2013年进行的5 GHz甚长基线阵列观测的14个射电强窄线塞弗特1(NLS 1)星系的紧凑射电结构的检测。虽然我们的样品中有50%的源仅显示出致密的核心,但其余50%显示出核心喷流结构。测得的核心亮度温度范围从$10^{8.4}$到$10^{11.4}$ K,中位数为$10^{10.1}$ K,这表明射电发射来自非热喷流,并且很可能大多数源都没有强烈的光束,这意味着这些射电大声的NLS 1星系中的喷流速度较低。结合在多个频率下采集的档案数据,我们发现七个源显示出平坦甚至倒置的无线电频谱,而其余七个对象则显示出陡峭的频谱。虽然所有这些来源都是非常响亮的无线电与$R > 100$,他们的喷流属性是不同的,在他们的毫角秒(mas)尺度(pc尺度)形态和他们的整体无线电频谱形状。低速喷射的证据(即,相对论性喷流较少),结合低动能/射电功率,可以解释大多数源中紧凑的VLBA射电结构。这些高吸积率系统中的温和相对论性喷流与一种情况是一致的,即喷流是由磁场和吸积盘的辐射力从盘上方的热日冕加速的。或者,低喷流体积速度可以解释为低自旋的布兰德福德-Znajek机制。

英文摘要:

We present the detection of compact radio structures of fourteen radio-loud narrow line Seyfert 1 (NLS1) galaxies from Very Long Baseline Array observations at 5 GHz, which were performed in 2013. While 50\% of the sources of our sample show a compact core only, the remaining 50\% exhibit a core-jet structure. The measured brightness temperatures of the cores range from $10^{8.4}$ to $10^{11.4}$ K with a median value of $10^{10.1}$ K, indicating that the radio emission is from non-thermal jets, and that, likely, most sources are not strongly beamed, then implying a lower jet speed in these radio-loud NLS1 galaxies. In combination with archival data taken at multiple frequencies, we find that seven sources show flat or even inverted radio spectra, while steep spectra are revealed in the remaining seven objects. Although all these sources are very radio-loud with $R > 100$, their jet properties are diverse, in terms of their milli-arcsecond (mas) scale (pc scale) morphology and their overall radio spectral shape. The evidence for slow jet speeds (i.e., less relativistic jets), in combination with the low kinetic/radio power, may offer an explanation for the compact VLBA radio structure in most sources. The mildly relativistic jets in these high accretion rate systems are consistent with a scenario, where jets are accelerated from the hot corona above the disk by the magnetic field and the radiation force of the accretion disk. Alternatively, a low jet bulk velocity can be explained by low spin in the Blandford-Znajek mechanism.

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