Thermal Evolution of an Active Region Through Quiet and Flaring Phases as Observed by NuSTAR, XRT, and AIA

Solar active regions contain plasma at a broad range of temperatures, with the thermal distribution often observed to peak in the few millions of kelvin (MK). Differential emission measure (DEM) analysis allows for multi-instrument observations of a single source to be combined to estimate the amount of material present as a function of temperature. By constructing DEMs, we can take advantage of the diverse temperature responses of solar-capable instruments observing across the electromagnetic spectrum. Hard x-ray (HXR) observations are uniquely sensitive to the high-temperature components of coronal plasma distributions, and are therefore essential for diagnosing hot (>5 MK) DEM components. The Nuclear Spectroscopic Telescope ARray (NuSTAR) is a powerful HXR observatory which makes periodic observations of the Sun. Combining NuSTAR’s HXR coverage with soft x-ray and extreme ultraviolet observations from Hinode/XRT and SDO/AIA, we present a detailed DEM analysis of an active region (NOAA designation AR 12671) observed for ~5 hours on 2018 May 29. Over the course of the interval, we show how the plasma temperature distribution of the active region evolves as the region produces several small microflares, and also undergoes quiescent periods without obvious HXR transients.