NuSTAR observations of the quietest Sun

Observing X-rays (above a few keV) from the Sun provides a direct insight into energy release (heating and/or particle acceleration) in the solar atmosphere. Targeting the faintest X-ray emission allows the study of the smallest solar flares, and their contribution to heating coronal loops. NuSTAR is an astrophysics telescope that uses directly focusing X-rays optics to detect weak X-rays from the Sun. We have observed the Sun many times since the start of solar pointings in Sep 2014 through to our latest observations in 2019. See http://ianan.github.io/nsovr/ for an overview. During the current solar minimum, NuSTAR has observed X-rays from a variety of sources when the Sun is devoid of active regions, during periods of the very quietest conditions. These sources have a variety of forms: diffuse sources, steady compact sources and brief flares/brightenings. The NuSTAR X-ray images of these weak sources are related to features seen at other wavelengths, such as in softer X-rays with Hinode/XRT and EUV with SDO/AIA. Crucially, NuSTAR’s imaging spectroscopy allows us to obtain and fit the X-ray spectrum from these small events determining their thermal properties. We will present some of the latest solar observations with NuSTAR as we go through the current solar minimum.