Speaker
Description
Solar flare hard X-ray (HXR) emission is conventionally interpreted within a thin-target / thick-target dichotomy, corresponding to coronal looptop and chromospheric footpoint sources respectively. Solar filaments, with characteristic densities of 10e10–10e11cme−3, occupy an intermediate density regime that fits neither limit. Motivated by this gap, we examine two failed filament eruptions in which Solar Orbiter/STIX reveals non-thermal coronal HXR emission spatially associated with the confined filament: (i) the partially-occulted event of 2022 May 3, in which the STIX peak occurs during the deceleration—rather than the initiation—phase of the rising filament; and (ii) the 2024 September 30 event, observed jointly by STIX and EUI/HRI at 2-second cadence, allowing fine-scale comparison between the HXR sources and the filament structure. We discuss the possibility that the filament itself acts as a "hybrid-target" bremsstrahlung emitter—neither cleanly thin nor cleanly thick—and outline the imaging-spectroscopy diagnostics required to test this picture, including footpoint–filament spectral index contrasts and inferred target column densities.