Hardware upgrades and science outcomes from the latest flights of the FOXSI rocket

FOXSI (which stands for the Focusing Optics X-ray Solar Imager) is a sounding rocket payload that has completed three successful flights supported by the Low-Cost Access to Space (LCAS) program of NASA. FOXSI stands out for being the first telescope optimized to use direct focusing to perform imaging spectroscopy of solar hard X-rays (HXRs). We present the latest instrument upgrades incorporated into the rocket payload for its third flight. We highlight the way these upgrades substantially improved the telescope performance and we present the observations obtained. Particularly, we describe the strategies implemented to reduce stray-light (ghost-ray) background and the inclusion of a soft X-ray CMOS sensor as well as HXR CdTe strip detectors to widen the spectral range of the telescope.

We finalize with an overview of the science results of the FOXSI flights. We present a differential emission measure (DEM) and thermal analyses of microflares observed during the second flight. We prove the relevance of the FOXSI measurements for obtaining unprecedented constrained microflare DEMs and discuss their implications on the energetics of these small flaring events. We finish presenting a discussion on the FOXSI measurements of an aged active region and quiet-sun areas observed during its latest flight.