Presentation #124.06 in the session High-Energy Solar Investigations Through Next-Generation Remote Sensing: Spectroscopy, Imaging, and Beyond — Poster Session.
Solar flares are known to accelerate electrons to high energies efficiently. However, how the underlying acceleration mechanism works remains poorly understood. The angular distribution of the accelerated electrons and the resultant hard X-ray emission and specifically, its polarization and directional anisotropy are the key to solve this mystery. The solar PolArization and Directivity X-Ray Experiment (PADRE) is a 12U Cubesat observatory that will observe the Sun in hard X-ray (HXRs) from low earth orbit. PADRE will investigate the accelerated electron angular distribution in solar flares with two unique and complementary approaches (1) by making spatially-integrated spectro-polarimetric x-ray measurements (~10-100 keV) and (2) by coordinating with Solar Orbiter/STIX to make the first two point measurements of x-rays and determining their directivity. We present the PADRE observatory concept, its science objectives, design and updates. We will discuss the type of observations that will be made by its two instruments (SHARP and XDSOX). Spectro-polarimetric observations will provide unique information of the electron angular distribution. Furthermore, STIX on board Solar Orbiter will perform X-ray observations of solar flares from 0.28 AU (at perihelion) to 1.2AU (at aphelion) and up to inclinations of ~25 degrees at heliospheric angles significantly different from the Earth. PADRE in collaboration with Solar Orbiter/STIX will provide a unique opportunity to make stereoscopic X-ray observations and measure the electron anisotropy of individual flares confidently for the first time. PADRE has one science objective: determine the angular distribution of accelerated electrons from standalone and joint SolO/STIX observations. This will allow the determination of the angular distribution of flare-accelerated electrons. The observational campaigns of STIX and PADRE with its directivity observations and the unique polarization measurements that will be performed by PADRE are two independent and complementary measurements. These observations are two independent anisotropy diagnostics that can be compared to validate the current particle acceleration mechanism models.