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NuSTAR and IRIS Co-observation of Microflare-Accelerated Electrons

Presentation #126.05 in the session Explosive Energy Release Processes in the Solar Corona and Earth’s Magnetosphere — Poster Session.

Published onOct 20, 2022
NuSTAR and IRIS Co-observation of Microflare-Accelerated Electrons

The Nuclear Spectroscopic Telescope ARray (NuSTAR) uses direct-focusing Hard X-Ray (HXR) telescopes to study astrophysical sources, and is capable of performing solar observations. NuSTAR’s direct-focusing optics provide high sensitivity to observe transient brightenings of microflares below GOES class B. The HXR regime is particularly useful for measuring nonthermal electron distributions and flare-heated plasma on the order of 5-10 MK, both via bremsstrahlung radiation (Grefenstette 2016). Investigation of nonthermal emission in these microflares, made possible by NuSTAR’s sensitivity, expands our understanding of particle acceleration to fainter flares, and gives important insight on similarities in the energy makeup between large and small flares.

In conjunction with the increasingly organized multi-instrument campaigns centered around Parker Solar Probe’s (PSP) perihelia, NuSTAR observed the Sun on April 29th, 2021, along with the Interface Region Imaging Spectrograph (IRIS) and the radio observatory the Very Large Array (VLA). This co-observation presents powerful opportunities for the joint study of flare-accelerated electrons and how these high-energy electrons affect the local plasma. During this observation, the IRIS slit that is capable of spectroscopy was aligned atop the same flaring region contained in NuSTAR’s FOV. Doppler blueshifting of the Silicon IV emission line is indicative of nonthermal activity with IRIS (Testa 2014), and was seen in initial IRIS analysis for this observation. Initial NuSTAR investigation also suggests the possibility of flare-accelerated particles present in at least 1 flare. A full spectral, spatial and temporal characterization of the flares that show possible nonthermal signatures within this NuSTAR observation will be presented. This joint analysis presents potential for the observation of both nonthermal emission signatures in the transition region with IRIS, and direct observation of the accelerated electron distribution at the flare source with NuSTAR. By combining the available analysis methods, greater knowledge of nonthermal emission within microflares may be achieved than with previous independent observations.

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