Viewing Radiation Signatures of Solar Energetic Particles in Interplanetary Space
AIR FORCE RESEARCH LAB HANSCOM AFB MA SPACE VEHICLES DIRECTORATE
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A current serious limitation on the studies of solar energetic particle SEP events is that their properties in the inner heliosphere are studied only through in situ spacecraft observations. Our understanding of spatial distributions and temporal variations of SEP events has come through statistical studies of many such events over several solar cycles. In contrast, flare SEPs in the solar corona can be imaged through their radiative and collisional interactions with solar fields and particles. We suggest that the heliospheric SEPs may also interact with heliospheric particles and fields to produce signatures which can be remotely observed and imaged. A challenge with any such candidate signature is to separate it from that of flare SEPs. The optimum case for imaging high-energy heliospheric protons may be the emission following proton collisions with solar wind SW ions. In the case of MeV electrons, gyrosynchotron radio emission may be the most readily detectible signal. In both cases we may already have observed one or two such events. Another radiative signature from nonthermal particles may be resonant transition radiation, which has likely already been observed from solar flare electrons We discuss energetic neutrons as another possible remote signature, but we rule out y-ray line and 0.511 MeV positron annihilation emission as observable signatures of heliospheric energetic ions.