Joint X-ray, EUV and UV Observations of a Small Microflare

Abstract

We present the first joint observation of a small microflare in X-rays with the Nuclear Spectroscopic Telescope ARray (NuSTAR), UV with the Interface Region Imaging Spectrograph (IRIS) and EUV with the Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA). These combined observations allows us to study the microflare's hot coronal and cooler chromospheric/transition region emission. This small microflare peaks from SOL2016-07-26T23:35 to 23:36UT, in both NuSTAR, SDO/AIA and IRIS. Spatially this corresponds to a small loop visible in the SDO/AIA Fe XVIII emission, which matches a similar structure lower in the solar atmosphere seen by IRIS in SJI1330Å and 1400Å. The NuSTAR emission in both 2.5-4 keV and 4-6 keV, is located in a small source at this loop location. The IRIS slit was over the microflaring loop, and fits show little change in Mg II but do show intensity increases, slight width enhancements and redshifts in Si IV andO IV, indicating that this microflare had most significance in and above the upper chromosphere. The NuSTAR microflare spectrum is well fitted by a thermal component of 5.8MK and $2.3\times 10^{44}$ cm${}^{-3}$, which corresponds to a thermal energy of $10^{26}$ erg, making it considerably smaller than previously studied X-ray microflares. No non-thermal emission was detected but this could be due to the limited effective exposure time of the observation. This observation shows that even ordinary features seen in UV and EUV, can remarkably have a higher energy component that is clear in X-rays.

Accepted for publication in ApJ

References in corpus (12)

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• Observations of the Quiet Sun During the Deepest Solar Minimum of the Past Century with Chandrayaan-2 XSM -- Sub-A Class Microflares Outside Active Regions
• NuSTAR Observation of a Minuscule Microflare in a Solar Active Region
• NuSTAR Observation of Energy Release in Eleven Solar Microflares
• FOXSI-2 Solar Microflares II: Hard X-ray Imaging Spectroscopy and Flare Energetics
• Spectroscopic evidence of cool plasma in quiet Sun HRIEUV small scale brightenings
• Multi-wavelength observations by XSM, Hinode and SDO of an active region. Chemical abundances and temperatures
• Diagnosing the Optically Thick/Thin Features Using the Intensity Ratio of Si IV Resonance Lines in Solar Flares
• The First Survey of Quiet Sun Features Observed in Hard X-Rays With NuSTAR
• First joint X-ray solar microflare observations with NuSTAR and Solar Orbiter/STIX
• A new view of the solar interface region from the Interface Region Imaging Spectrograph (IRIS)
• Detecting non-thermal emission in a solar microflare using nested sampling
• Quiet Sun impulsive events observed with NuSTAR during solar minimum