Multi-Epoch VERA Observations of Sagittarius A*. I. Images and Structural Variability
Multi-Epoch VERA Observations of Sagittarius A*. I. Images and Structural Variability
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DOI：
10.1093/pasj/65.4.91
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发表时间：
2013-08
影响因子：
2.3
通讯作者：
K. Akiyama;R. Takahashi;M. Honma;T. Oyama;H. Kobayashi
中科院分区：
文献类型：
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作者：
K. Akiyama;R. Takahashi;M. Honma;T. Oyama;H. Kobayashi
我们报告的结果，多历元观测的Sgr A* 与VLBI探测射电天体测量（VERA）在43 GHz的，从2004年至2008年进行。我们检测到通量的时间变化在11%的水平和内在的大小在19%。此外，与以前的甚长基线阵列（VLBA）结果的比较表明，Sgr A* 在2007年5月经历了至少超过10天的耀斑事件。Sgr A* 的本征尺寸与耀斑事件前后的尺寸相比保持在1级以内不变，表明Sgr A* 的亮温度有所增加。耀斑事件发生在31 d内，比折射时间尺度短。此外，简单的星际散射模型很难解释耀斑事件时光谱指数的增加。因此，燃烧事件最有可能与Sgr A* 内在性质的变化有关。我们考虑了亮温变化的原因，认为Sgr A* 的耀斑事件可以用电子的持续加热来解释，例如吸积流中的驻激波。
We report the results of multi-epoch observations of Sgr A* with VLBI Exploration of Radio Astrometry (VERA) at 43 GHz, carried out from 2004 to 2008. We detected a time variation of flux at 11 % level and intrinsic size at 19 %. In addition, comparisons with previous Very Long Baseline Array (VLBA) results shows that Sgr A* underwent the flaring event at least longer than 10 days in May 2007. The intrinsic size of Sgr A* remained unchanged within 1 � level from the size before/after the flaring event, indicating that the brightness temperature of Sgr A* was increased. The flaring event occurred within 31 d, which is shorter than the refractive time scale. Moreover it is difficult to explain the increase in the spectral index at the flaring event by the simple interstellar scattering model. Hence, the flaring event is most likely associated with the changes in intrinsic properties of Sgr A*. We considered the origin of the brightness temperature variation, and concluded that the flaring event of Sgr A* could be explained by the continuous heating of electrons, such as a standing shock in accretion flow.