The First Focused Hard X-ray Images of the Sun with NuSTAR

TL;DR

This paper reports the first dedicated hard X-ray imaging of the Sun using NuSTAR, demonstrating its capabilities and initial scientific results in solar observations at energies above 3 keV.

Contribution

It introduces NuSTAR's solar observation techniques, discusses their limitations, and presents initial high-energy solar images and spectral measurements.

Findings

Detection of Fe K-shell lines in a solar flare

Hard X-ray emission from the high corona

Full-disk hard X-ray solar images

Abstract

We present results from the the first campaign of dedicated solar observations undertaken by the \textit{Nuclear Spectroscopic Telescope ARray} ({\em NuSTAR}) hard X-ray telescope. Designed as an astrophysics mission, {\em NuSTAR} nonetheless has the capability of directly imaging the Sun at hard X-ray energies ($>$3~keV) with an increase in sensitivity of at least two magnitude compared to current non-focusing telescopes. In this paper we describe the scientific areas where \textit{NuSTAR} will make major improvements on existing solar measurements. We report on the techniques used to observe the Sun with \textit{NuSTAR}, their limitations and complications, and the procedures developed to optimize solar data quality derived from our experience with the initial solar observations. These first observations are briefly described, including the measurement of the Fe K-shell lines in a decaying X-class flare, hard X-ray emission from high in the solar corona, and full-disk hard X-ray images of the Sun.