RHESSI X-ray and Gamma-ray observations of the January 20, 2005 event

Spacecraft and ground-based solar observations of the January 20, 2005 flare are summarized with a focus on X-ray and Gamma-ray observations from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). X-ray and Gamma-ray observations are excellent diagnostics of accelerated particles: Accelerated electrons colliding with the ambient solar atmosphere produce bursts of bremsstrahlung hard X-rays; and collisions of accelerated ions with the atmosphere result in a complex spectrum of narrow and broad gamma-ray lines. In the January 20 flare, HXR emission is observed from footpoints of the flare loop. The statistics in the 2.2 MeV line emission is rather poor and a detailed spatial comparison with HXR images is inconclusive. The spectral evolution in HXRs during the main peak shows hardening during the event (so-called 'soft-hard-harder' behavior) as often observed from flares related to solar energetic particle events (Kiplinger 1995). The flare accelerated proton spectrum derived from the Gamma-ray observations is flat with a power law index of 2.3±0.3 and is surprisingly similar to the insitu observed proton spectrum near 1~AU (2.1±0.1). This suggest that the insitu observed protons are possibly flare associated and not necessarily shock accelerated. We will discuss this possibility also considering the relative timing between flare emissions, the coronal mass ejection, and the onset of solar energetic particles observed at 1 AU.