Unprecedented Near-infrared Brightness and Variability of Sgr A*
Unprecedented Near-infrared Brightness and Variability of Sgr A*
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DOI：
10.3847/2041-8213/ab38c3
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发表时间：
2019-09
期刊：
影响因子：
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通讯作者：
T. Do;G. Witzel;A. Gautam;Zhuo Chen;A. Ghez;M. Morris;E. Becklin;A. Ciurlo;M. Hosek;
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文献类型：
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作者：
T. Do;G. Witzel;A. Gautam;Zhuo Chen;A. Ghez;M. Morris;E. Becklin;A. Ciurlo;M. Hosek;
银河系中心超大质量黑洞的电磁对应物Sgr A* 已经在近红外线上观测了20多年，并且已知是高度可变的。我们报告了新的凯克望远镜观测结果，显示Sgr A* 在2019年达到了比以往任何时候都在近红外波长下测量到的更明亮的通量水平。在K′波段，Sgr A* 的通量达到了106 mJy，是之前用甚大望远镜和凯克望远镜在130个夜晚进行的超过13，000次测量中观测到的峰值通量的两倍。我们还观察到在2小时的时间跨度内通量变化75倍，在1.6和2.1 μm之间没有明显的颜色变化。今年观测到的通量变化分布也与历史分布有很大不同。使用已发表的最全面的统计模型，考虑到凯克的历史观测，今年观测到的一个夜晚出现峰值通量水平的概率小于0.3%。观测到与2019年所有四个夜晚数据相似的通量水平的概率小于0.05%。这种亮度和可变性的增加可能表明Sgr A* 的活动增强或其吸积状态的变化。这也可能表明，目前的模型不足以模拟高通量水平下的Sgr A*，应予以更新。Sgr A* 前所未有的亮度的潜在物理起源可能是由于星星S 0 -2在2018年最接近黑洞的通道导致的吸积流的变化，或者是2014年尘埃物体G2接近的延迟反应。额外的多波长观测将是必要的，以监测Sgr A* 的潜在状态变化，并限制其当前可变性的物理过程。
The electromagnetic counterpart to the Galactic center supermassive black hole, Sgr A*, has been observed in the near-infrared for over 20 yr and is known to be highly variable. We report new Keck Telescope observations showing that Sgr A* reached much brighter flux levels in 2019 than ever measured at near-infrared wavelengths. In the K′ band, Sgr A* reached flux levels of ∼6 mJy, twice the level of the previously observed peak flux from >13,000 measurements over 130 nights with the Very Large Telescope and Keck Telescopes. We also observe a factor of 75 change in flux over a 2 hr time span with no obvious color changes between 1.6 and 2.1 μm. The distribution of flux variations observed this year is also significantly different than the historical distribution. Using the most comprehensive statistical model published, the probability of a single night exhibiting peak flux levels observed this year, given historical Keck observations, is less than 0.3%. The probability of observing flux levels that are similar to all four nights of data in 2019 is less than 0.05%. This increase in brightness and variability may indicate a period of heightened activity from Sgr A* or a change in its accretion state. It may also indicate that the current model is not sufficient to model Sgr A* at high flux levels and should be updated. Potential physical origins of Sgr A*'s unprecedented brightness may be from changes in the accretion flow as a result of the star S0-2's closest passage to the black hole in 2018, or from a delayed reaction to the approach of the dusty object G2 in 2014. Additional multi-wavelength observations will be necessary to both monitor Sgr A* for potential state changes and to constrain the physical processes responsible for its current variability.