Collimation, Acceleration, and Recollimation Shock in the Jet of Gamma-Ray Emitting Radio-loud Narrow-line Seyfert 1 Galaxy 1H0323+342
Collimation, Acceleration, and Recollimation Shock in the Jet of Gamma-Ray Emitting Radio-loud Narrow-line Seyfert 1 Galaxy 1H0323+342
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DOI：
10.3847/1538-4357/aac49f
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发表时间：
2018-05
期刊：
影响因子：
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通讯作者：
K. Hada;A. Doi;K. Wajima;F. D’Ammando;M. Orienti;M. Giroletti;G. Giovannini;M. Nakamura;K. Asada
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作者：
K. Hada;A. Doi;K. Wajima;F. D’Ammando;M. Orienti;M. Giroletti;G. Giovannini;M. Nakamura;K. Asada
我们利用高分辨率多频甚长基线阵列观测研究了1H 0323+342喷流的详细射电结构。这个源被称为最近的γ射线发射射电大声窄线塞弗特1（NLS 1）星系。我们发现，内部射流的形态是很好的特点是由一个抛物线形状，表明射流是连续准直附近的射流基地。另一方面，我们发现射流在更大的尺度上膨胀得更快，从而形成圆锥形。“准直中断”的位置与距地核7 mas处的明亮准定常特征相一致（对应于约100 pc的去投影距离），在那里喷流宽度与高度偏振的信号一起局部收缩，表明是一个准定常激波。我们发现，准直区与喷流速度逐渐加快的区域重合，表明喷流加速区与准直区共存，最后形成准直激波，这可能是费米LAT探测到的高能γ射线耀斑的潜在位置。值得注意的是，1H 0323+342喷流的这些观测特征总体上与附近的射电星系M87和HST-1以及一些耀变体非常相似，这表明可能存在共同的喷流形成机制。基于两个源喷流剖面的相似性，我们还简要讨论了1H 0323+342中心黑洞的质量，这在该源和NLS 1中仍然是非常有争议的。
We investigated the detailed radio structure of the jet of 1H 0323+342 using high-resolution multifrequency Very Long Baseline Array observations. This source is known as the nearest γ-ray emitting radio-loud narrow-line Seyfert 1 (NLS1) galaxy. We discovered that the morphology of the inner jet is well characterized by a parabolic shape, indicating that the jet is continuously collimated near the jet base. On the other hand, we found that the jet expands more rapidly at larger scales, resulting in a conical shape. The location of the “collimation break” is coincident with a bright quasi-stationary feature at 7 mas from core (corresponding to a deprojected distance on the order of ∼100 pc), where the jet width locally contracts together with highly polarized signals, suggesting a recollimation shock. We found that the collimation region is coincident with the region where the jet speed gradually accelerates, suggesting a coexistence of the jet acceleration and collimation zone, ending up with the recollimation shock, which could be a potential site of high-energy γ-ray flares detected by the Fermi-LAT. Remarkably, these observational features of the 1H 0323+342 jet are overall very similar to those of the nearby radio galaxy M87 and HST-1 as well as some blazars, suggesting that a common jet formation mechanism might be at work. Based on the similarity of the jet profile of the two sources, we also briefly discuss the mass of the central black hole of 1H 0323+342, which is also still highly controversial in this source and NLS1s in general.