A Strong Radio Brightening at the Jet Base of M 87 during the Elevated Very High Energy Gamma-Ray State in 2012
A Strong Radio Brightening at the Jet Base of M 87 during the Elevated Very High Energy Gamma-Ray State in 2012
复制标题
2012 年高能伽玛射线状态下 M 87 喷气机基地的强烈射电增亮
DOI：
10.1088/0004-637x/788/2/165
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
A.; Na
中科院分区：
文献类型：
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作者：
Hada;K.; Giroletti;M.; Kino;M.; Giovannini;G.; D'Ammando;F.; Cheung;C. C.; Beilicke;M.; Nagai;H.; Doi;A.; Akiyama;K.; Honma;M.; Niinuma;K.; Casadio;C.; Orienti;M.; Krawczynski;H.; Gomez;J. L.; Sawada-Satoh;S.; Koyama;S.; Cesarini;A.; Na
本文报道了2011年2月至2012年10月，利用VLBI射电天文探测（VERA）和欧洲VLBI网络（EVN）对m87喷射流的密集、高角分辨率无线电监测观测，以及费米大面积望远镜获得的同期高能(100 MeV< E< 100 GeV) γ射线光曲线。在此期间（特别是2012年2月至2012年3月），VERITAS报告了m87通量在非常高能(VHE; E bbb100 GeV) γ射线中的升高水平。我们检测到与VHE活动一致的22 GHz和43 GHz的未解析喷气基地（无线电核心）的无线电通量密度显著（高达70%）增加。与此同时，我们用5 GHz的EVN证实了特殊的结，HST-1，它是另一个受欢迎的γ射线产生位点，位于距离原子核约120pc处，在其通量密度和结构上保持静止。这些无线电波段的结果强烈表明，2012年的VHE γ射线活动起源于距中心超大质量黑洞0.03 pc或56史瓦西半径（43 GHz时VERA空间分辨率为0.4 mas）范围内的喷流基地。我们进一步对m87核心在耀斑期间的6个时期进行了VERA天文测量，检测到核心在22 ~ 43 GHz之间的偏移，其平均值与之前的天文测量结果相似。我们还发现了无线电核心耀斑在43,22和5ghz的明显频率依赖演化；在频率越高、幅度越大的情况下，射电通量密度增加得越快，光曲线在22 GHz和43 GHz的峰值之间明显存在时滞，其值被限制在~ 35-124天之间。这表明在VHE事件期间，在黑洞附近产生了一个新的无线电发射成分，然后向外传播，同步加速器不透明度逐渐降低。通过结合得到的核心位移和时延，我们估计了在22和43 GHz的核心之间的不透明区域传播的新生分量的表观速度。我们得出了该组件的亚光速速度（小于~ 0.2c）。这个数值比2008年突出的VHE耀斑事件期间从核心出现的超光（~ 1.1c）特征要慢得多，这表明m87中更强的VHE活动可能与产生更高的洛伦兹因子射流有关。
We report our intensive, high angular resolution radio monitoring observations of the jet in M 87 with the VLBI Exploration of Radio Astrometry (VERA) and the European VLBI Network (EVN) from 2011 February to 2012 October, together with contemporaneous high-energy (100 MeV< E< 100 GeV) γ-ray light curves obtained by the Fermi Large Area Telescope. During this period (specifically from 2012 February to 2012 March), an elevated level of the M 87 flux is reported at very high energy (VHE; E> 100 GeV) γ rays by VERITAS. We detected a remarkable (up to∼ 70%) increase of the radio flux density from the unresolved jet base (radio core) with VERA at 22 and 43 GHz coincident with the VHE activity. Meanwhile, we confirmed with EVN at 5 GHz that the peculiar knot, HST-1, which is an alternative favored γ-ray production site located at≳ 120 pc from the nucleus, remained quiescent in terms of its flux density and structure. These results in the radio bands strongly suggest that the VHE γ-ray activity in 2012 originates in the jet base within 0.03 pc or 56 Schwarzschild radii (the VERA spatial resolution of 0.4 mas at 43 GHz) from the central supermassive black hole. We further conducted VERA astrometry for the M 87 core at six epochs during the flaring period, and detected core shifts between 22 and 43 GHz, a mean value of which is similar to that measured in the previous astrometric measurements. We also discovered a clear frequency-dependent evolution of the radio core flare at 43, 22, and 5 GHz; the radio flux density increased more rapidly at higher frequencies with a larger amplitude, and the light curves clearly showed a time-lag between the peaks at 22 and 43 GHz, the value of which is constrained to be within∼ 35–124 days. This indicates that a new radio-emitting component was created near the black hole in the period of the VHE event, and then propagated outward with progressively decreasing synchrotron opacity. By combining the obtained core shift and time-lag, we estimated an apparent speed of the newborn component propagating through the opaque region between the cores at 22 and 43 GHz. We derived a sub-luminal speed (less than∼ 0.2c) for this component. This value is significantly slower than the super-luminal (∼ 1.1c) features that appeared from the core during the prominent VHE flaring event in 2008, suggesting that stronger VHE activity can be associated with the production of a higher Lorentz factor jet in M 87.