Long-term millimeter VLBI monitoring of M87 with KVN at milliarcsecond resolution: nuclear spectrum
Long-term millimeter VLBI monitoring of M87 with KVN at milliarcsecond resolution: nuclear spectrum
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DOI：
10.1051/0004-6361/201732421
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发表时间：
2018-02-19
影响因子：
6.5
通讯作者：
Kang, Sincheol
中科院分区：
文献类型：
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作者：
Kim, Jae-Young;Lee, Sang-Sung;Kang, Sincheol
利用韩国VLBI网络（KVN）获得的4年完全同步的多频VLBI数据，研究了射电星系M87核心在小于或近似于0.8 mas（110 R（s））空间尺度下厘米至毫米波长的同步辐射光谱。我们发现一个核心的光谱指数α大于或接近-0.37（S正比于nu（+ α））之间的22和129 GHz。通过结合分辨率匹配的通量测量从甚长基线阵列（VLBA）在15 GHz和事件地平线望远镜（EHT）230 GHz的核心通量测量在2009年和2012年作为下限，我们发现一个几乎平坦的核心频谱跨越15和129 GHz，这可以自然地连接230 GHz的VLBI核心通量的证据。非常平坦的光谱是一个强有力的指示，射流基础不包括一个简单的均匀等离子体，但不均匀的多能量分量，至少有一个组件的翻转频率大于或接近100 GHz。如果强磁化（紧凑，在>100 GHz处光学厚）和相对弱磁化（更扩展，在>100 GHz处光学薄）都可以定性地解释光谱形状。
We study the centimeter-to millimeter-wavelength synchrotron spectrum of the core of the radio galaxy M87 at less than or similar to 0.8 mas similar to 110R(s) spatial scales using four years of fully simultaneous, multi-frequency VLBI data obtained by the Korean VLBI Network (KVN). We find a core spectral index alpha of greater than or similar to-0.37 (S proportional to nu(+alpha)) between 22 and 129 GHz. By combining resolution-matched flux measurements from the Very Long Baseline Array (VLBA) at 15 GHz and taking the Event Horizon Telescope (EHT) 230 GHz core flux measurements in epochs 2009 and 2012 as lower limits, we find evidence of a nearly flat core spectrum across 15 and 129 GHz, which could naturally connect the 230 GHz VLBI core flux. The extremely flat spectrum is a strong indication that the jet base does not consist of a simple homogeneous plasma, but of inhomogeneous multi-energy components, with at least one component with the turn-over frequency greater than or similar to 100 GHz. The spectral shape can be qualitatively explained if both the strongly (compact, optically thick at >100 GHz) and the relatively weakly magnetized (more extended, optically thin at