NuSTAR Detection of X-Ray Heating Events in the Quiet Sun
NuSTAR Detection of X-Ray Heating Events in the Quiet Sun
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DOI：
10.3847/2041-8213/aab889
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发表时间：
2018-03
期刊：
影响因子：
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通讯作者：
M. Kuhar;S. Krucker;L. Glesener;I. Hannah;B. Grefenstette;David M. Smith;H. Hudson;S. White
中科院分区：
文献类型：
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作者：
M. Kuhar;S. Krucker;L. Glesener;I. Hannah;B. Grefenstette;David M. Smith;H. Hudson;S. White
对日冕加热问题的解释可能在于纳米耀斑的存在，即整个太阳盘面上发生的许多小规模加热事件。在这封信中，我们介绍了在2016年7月26日和2017年3月21日的核光谱望远镜ARray（努斯塔）太阳活动期间，与太阳动力学观测台/大气成像组件（SDO/AIA）观测同时进行的三次安静太阳耀斑的首次成像光谱X射线观测。这三个事件中有两个显示出X射线峰值和极紫外线辐射之间的几分钟时间滞后。在3.2-4.1 MK范围内的相当低的温度下的等温拟合和（0.6-15）× 1044 cm−3的发射测量很好地描述了它们的光谱，导致热能在（2-6）× 1026 erg范围内。努斯塔光谱未显示任何非热或高温成分的迹象。然而，由于（隐藏的）非热能的估计上限与热能估计相当，因此在观察到的光谱中缺乏非热分量不是一个约束结果。估计地球静止业务环境卫星（GOES）类从温度和排放量的拟合值之间的1/1000和1/100 A级的水平下降，使它们的软X射线通量比最大的太阳耀斑暗八个数量级。
The explanation of the coronal heating problem potentially lies in the existence of nanoflares, numerous small-scale heating events occurring across the whole solar disk. In this Letter, we present the first imaging spectroscopy X-ray observations of three quiet Sun flares during the Nuclear Spectroscopic Telescope ARray (NuSTAR) solar campaigns on 2016 July 26 and 2017 March 21, concurrent with the Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) observations. Two of the three events showed time lags of a few minutes between peak X-ray and extreme ultraviolet emissions. Isothermal fits with rather low temperatures in the range 3.2–4.1 MK and emission measures of (0.6–15) × 1044 cm−3 describe their spectra well, resulting in thermal energies in the range (2–6) × 1026 erg. NuSTAR spectra did not show any signs of a nonthermal or higher temperature component. However, as the estimated upper limits of (hidden) nonthermal energy are comparable to the thermal energy estimates, the lack of a nonthermal component in the observed spectra is not a constraining result. The estimated Geostationary Operational Environmental Satellite (GOES) classes from the fitted values of temperature and emission measure fall between 1/1000 and 1/100 A class level, making them eight orders of magnitude fainter in soft X-ray flux than the largest solar flares.