Dual-perspective Microwave and Hard X-Ray Constraints of Asymmetric Nonthermal Loops in an X-class Flare

Abstract We report dual-perspective microwave and hard X-ray (HXR) observations of an X-class flare on 2024 May 15, taking advantage of the unique geometry of a front-side view from the Earth and a back-side perspective from the Solar Orbiter. Using spatially resolved imaging spectroscopy from Siberian Radioheliograph together with Chashan Broadband Solar millimeter spectrometer and Spectrometer Telescope for Imaging X-rays data, we identify a set of nonthermal flaring loops in an asymmetric magnetic field, with microwave sources located near the loop top and HXR sources associated with the southern footpoint. Compared with HXR, the microwave emission shows an opposite ascending trend, large time lags, and distinctive “soft–hard–harder” spectral patterns, which we attribute to energy-dependent trapping and precipitation of energetic electrons in an asymmetric magnetic configuration. Flux pulsations and their spectral and polarization signatures are consistent with intermittent particle acceleration rather than magnetohydrodynamic wave modulation. Microwave magnetic diagnostics, corroborated by nonlinear force free field extrapolation, provide key constraints on the three-dimensional magnetic configuration. The dual-perspective flux profile comparison and consistent quasiperiodic pulsation signatures across wavelengths together support a self-consistent picture of energy-dependent electron trapping, precipitation, and transport in these asymmetric loops.