Microflare Heating of a Solar Active Region Observed with NuSTAR, Hinode/XRT, and SDO/AIA
Microflare Heating of a Solar Active Region Observed with NuSTAR, Hinode/XRT, and SDO/AIA
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DOI：
10.3847/1538-4357/aa7a59
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发表时间：
2017-06
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影响因子：
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通讯作者：
P. Wright;I. Hannah;B. Grefenstette;L. Glesener;S. Krucker;H. Hudson;David M. Smith;A. Marsh;S. White;M. Kuhar
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文献类型：
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作者：
P. Wright;I. Hannah;B. Grefenstette;L. Glesener;S. Krucker;H. Hudson;David M. Smith;A. Marsh;S. White;M. Kuhar
NuSTAR 是一台高灵敏度聚焦硬 X 射线 (HXR) 望远镜，在其初始太阳指向中观察到了几个小微耀斑。在本文中，我们提出了 2015 年 4 月 29 日世界标准时间约 11:29 与 NuSTAR 和 Hinode/XRT 首次联合观测到的微耀斑。这种微耀斑显示材料被加热到几百万开尔文，通过 Hinode/XRT 在软 X 射线中观察到，并且通过 SDO/AIA 在极紫外光中微弱可见。对于该区域的四个 NuSTAR 观测中的三个（耀斑前、衰变和耀斑后阶段），光谱与 3.2-3.5 MK 的单一热模型很好地拟合，但脉冲阶段的光谱显示高达 10 MK 的额外发射，相当于 A0.1 GOES 级别的发射。我们使用 SDO/AIA、Hinode/XRT 和 NuSTAR 恢复差分发射测量 (DEM)，提供前所未有的温度覆盖范围。我们发现耀斑前的 DEM 在 ∼3 MK 处达到峰值，并在 5 MK 处急剧下降；但在微耀斑的脉冲阶段，3 MK 以上的发射更亮，并延伸至 10 MK，加热速率约为 erg s−1。由于 NuSTAR 光谱是纯热光谱，我们确定了可能的非热轫致辐射的上限。我们发现，要使加速电子成为热源，需要具有低能量截止 keV 的幂律谱。总之，这第一个 NuSTAR 微耀斑与更强大的耀斑非常相似。
NuSTAR is a highly sensitive focusing hard X-ray (HXR) telescope and has observed several small microflares in its initial solar pointings. In this paper, we present the first joint observation of a microflare with NuSTAR and Hinode/XRT on 2015 April 29 at ∼11:29 UT. This microflare shows the heating of material to several million Kelvin, observed in soft X-rays with Hinode/XRT, and was faintly visible in the extreme ultraviolet with SDO/AIA. For three of the four NuSTAR observations of this region (pre-flare, decay, and post-flare phases), the spectrum is well fitted by a single thermal model of 3.2–3.5 MK, but the spectrum during the impulsive phase shows additional emission up to 10 MK, emission equivalent to the A0.1 GOES class. We recover the differential emission measure (DEM) using SDO/AIA, Hinode/XRT, and NuSTAR, giving unprecedented coverage in temperature. We find that the pre-flare DEM peaks at ∼3 MK and falls off sharply by 5 MK; but during the microflare’s impulsive phase, the emission above 3 MK is brighter and extends to 10 MK, giving a heating rate of about erg s−1. As the NuSTAR spectrum is purely thermal, we determined upper limits on the possible non-thermal bremsstrahlung emission. We find that for the accelerated electrons to be the source of heating, a power-law spectrum of with a low-energy cutoff keV is required. In summary, this first NuSTAR microflare strongly resembles much more powerful flares.