标题： NuSTAR对太阳活动区中一个微小耀斑的观测 显示英文标题

标题： NuSTAR Observation of a Minuscule Microflare in a Solar Active Region

摘要： 我们展示了对最弱的活动区(AR)微耀斑之一的X射线成像光谱分析。 该微耀斑发生在2018年9月9日$\sim$11:04 UT，我们使用核光谱望远镜阵列(NuSTAR)和太阳动力学天文台的大气成像组件(SDO/AIA)对其进行研究。 该微耀斑在2.5-7 keV范围内由NuSTAR清晰观测到，并在来自SDO/AIA通道94$\unicode{x212B}$更热成分的Fe XVIII发射中得到证实。 我们估计该事件的能量比GOES A级微耀斑低三个数量级，能量为1.1$\times$10$^{26}$erg。 其温度达到6.7 MK，发射量为8.0$\times$10$^{43}$cm$^{-3}$。 未检测到非热辐射，但我们确定了此类辐射的上限。 我们提出了文献中活动区微耀斑的最低热能估计值，这处于仍被认为是X射线微耀斑的下限。 显示英文摘要

摘要： We present X-ray imaging spectroscopy of one of the weakest active region (AR) microflares ever studied. The microflare occurred at $\sim$11:04 UT on 2018 September 9 and we studied it using the Nuclear Spectroscopic Telescope ARray (NuSTAR) and the Solar Dynamic Observatory's Atmospheric Imaging Assembly (SDO/AIA). The microflare is observed clearly in 2.5-7 keV with NuSTAR and in Fe XVIII emission derived from the hotter component of the 94 $\unicode{x212B}$ SDO/AIA channel. We estimate the event to be three orders of magnitude lower than a GOES A class microflare with an energy of 1.1$\times$10$^{26}$ erg. It reaches temperatures of 6.7 MK with an emission measure of 8.0$\times$10$^{43}$ cm$^{-3}$. Non-thermal emission is not detected but we instead determine upper limits to such emission. We present the lowest thermal energy estimate for an AR microflare in literature, which is at the lower limits of what is still considered an X-ray microflare.