Authors: A.T. Bogdanov, B. Klecker, E. Möbius,
M. Hilchenbach, L.M. Kistler,
M.A.Popecki, D. Hovestadt, J. Weygand
Reference: Proceedings of the 26th International Cosmic Ray Conference, Vol 6, pp 179 (1999)
Abstract:
We investigate the energy dependence of the charge states of
heavy ions during a number of gradual solar energetic particle events
related to coronal mass ejections. The data of two instruments with
complementary energy ranges, the Solar Energetic Particle Ionic Charge
Analyzer SEPICA on ACE and the time-of-flight mass and charge
spectrometer STOF on SOHO are used to cover the energy range from ~ 0.02
to 0.7 MeV/amu for O and Fe. Measurements with SAMPEX and SEPICA/ACE
contain evidence that some gradual CME related SEP events show energy
dependent charge distributions. In the present paper we are closing the
gap in the lower energy interval (STOF data) thus making future
comparison to solar wind values - representative for coronal conditions
- more reliable. We find that energy dependent charge states of Fe are
almost ubiquitous in gradual SEP events. Very large differences from
event to event are observed however. In cases of local acceleration at
the CME driven shock the variation in the energy interval up to 0.5
MeV/amu is ~ 1-2 charge units. In alternative cases the mean ionic
charge variation for Fe reaches ~4 charge units over the same energy
interval. The respective charge spectra could be interpreted as the
result of ionization near the sun, in the dense coronal plasma, with or
without reaching charge state equilibrium.