Hard X‐Ray Spectral Evolution and Production of Solar Energetic Particle Events during the January 2005 X‐Class Flares

High-resolution hard X-ray observations provided by the Reuven Ramaty High Energy Solar Spectroscopic Imager ( RHESSI ) are used to study the spectral evolution of ~50-200 keV nonthermal electron bremsstrahlung emissions of five X-class flares observed during the January 2005 solar storm events. Four of these flares show progressive spectral hardening during at least some hard X-ray peaks, while only one event shows the otherwise more commonly observed soft-hard-soft behavior. Imaging observations reveal that ~50-100 keV nonthermal electron bremsstrahlung emissions originate from footpoints of flare loops at all times, including during times of progressive spectral hardening, indicating that the spectral hardening component is produced by precipitating electrons, and not by electrons trapped in the corona. The four flares with progressive spectral hardening are all related to solar energetic particle (SEP) events, while the only X-class flare with soft-hard-soft behavior is not. This finding is consistent with earlier studies, suggesting that electron acceleration and transport in flares is somehow linked to the production of SEPs escaping into interplanetary space.