Grant C. Weldon, T. Do, G. Witzel, A. Ghez, A. Gautam, E. Becklin, M. Morris, G. Martinez, S. Sakai, Jessica R. Lu, K. Matthews, M. Hosek, Zoë Haggard
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These observations reveal that the mean luminosity of Sgr A* increased by a factor of ∼3 in 2019, and the 2019 light curves had higher variance than in all time periods we examined. We find that the 2020–2022 flux distribution is statistically consistent with the historical sample and model predictions, but with fewer bright measurements above 0.6 mJy at the ∼2σ level. Since 2019, we have observed a maximum K s (2.2 μm) flux of 0.9 mJy, compared to the highest pre-2019 flux of 2.0 mJy and highest 2019 flux of 5.6 mJy. Our results suggest that the 2019 activity was caused by a temporary accretion increase onto Sgr A*, possibly due to delayed accretion of tidally stripped gas from the gaseous object G2 in 2014. We also examine faint Sgr A* fluxes over a long time baseline to search for a quasi-steady quiescent state. 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引用次数: 0
摘要
Sgr A*是与银河系中心超大质量黑洞吸积有关的可变电磁源。虽然Sgr A*的近红外(NIR)变化在过去20年里是一致的,但2019年前所未有的活动挑战了现有的统计模型。我们通过重新校准和重新分析凯克天文台Sgr A*从2005年到2022年的所有成像观测来调查这种活动的起源。采用激光导星自适应光学系统,在2.12 μm波段使用NIRC2成像仪,得到了69个观测历元的光曲线。这些观测结果表明,Sgr A*的平均光度在2019年增加了约3倍,2019年的光度曲线比我们研究的所有时间段都有更高的方差。我们发现,2020-2022年的通量分布在统计上与历史样本和模型预测一致,但在~ 2σ水平上,0.6 mJy以上的明亮测量较少。自2019年以来,我们观测到的最大K s (2.2 μm)通量为0.9 mJy,而2019年之前的最高通量为2.0 mJy, 2019年的最高通量为5.6 mJy。我们的研究结果表明,2019年的活动是由Sgr a *的暂时吸积增加引起的,可能是由于2014年气态物体G2的潮汐剥离气体的延迟吸积。我们还检查了Sgr A*在长时间基线上微弱的通量,以寻找准稳定的静止状态。我们发现Sgr A*显示出超过500倍的通量变化,在近红外波段没有静止状态的证据。
Near-infrared Flux Distribution of Sgr A* from 2005–2022: Evidence for an Enhanced Accretion Episode in 2019
Sgr A* is the variable electromagnetic source associated with accretion onto the Galactic center supermassive black hole. While the near-infrared (NIR) variability of Sgr A* was shown to be consistent over two decades, unprecedented activity in 2019 challenges existing statistical models. We investigate the origin of this activity by recalibrating and reanalyzing all of our Keck Observatory Sgr A* imaging observations from 2005–2022. We present light curves from 69 observation epochs using the NIRC2 imager at 2.12 μm with laser-guide star adaptive optics. These observations reveal that the mean luminosity of Sgr A* increased by a factor of ∼3 in 2019, and the 2019 light curves had higher variance than in all time periods we examined. We find that the 2020–2022 flux distribution is statistically consistent with the historical sample and model predictions, but with fewer bright measurements above 0.6 mJy at the ∼2σ level. Since 2019, we have observed a maximum K s (2.2 μm) flux of 0.9 mJy, compared to the highest pre-2019 flux of 2.0 mJy and highest 2019 flux of 5.6 mJy. Our results suggest that the 2019 activity was caused by a temporary accretion increase onto Sgr A*, possibly due to delayed accretion of tidally stripped gas from the gaseous object G2 in 2014. We also examine faint Sgr A* fluxes over a long time baseline to search for a quasi-steady quiescent state. We find that Sgr A* displays flux variations over a factor of ∼500, with no evidence for a quiescent state in the NIR.