OBSERVATIONS OF THE 2006 DECEMBER 13 AND 14 SOLAR PARTICLE EVENTS IN THE 80 MeV n^–1-3 GeV n^–1RANGE FROM SPACE WITH THE PAMELA DETECTOR

Abstract

We present the space spectrometer PAMELA observations of proton and helium\nfluxes during the December 13 and 14, 2006 solar particle events. This is the\nfirst direct measurement of the solar energetic particles in space with a\nsingle instrument in the energy range from $\\sim$ 80 MeV/n up to $\\sim$ 3\nGeV/n. In the event of December 13 measured energy spectra of solar protons and\nhelium were compared with results obtained by neutron monitors and other\ndetectors. Our measurements show a spectral behaviour different from those\nderived from the neutron monitor network. No satisfactory analytical fitting\nwas found for the energy spectra. During the first hours of the December 13\nevent solar energetic particles spectra were close to the exponential form\ndemonstrating rather significant temporal evolution. Solar He with energy up to\n~1 GeV/n was recorded on December 13. In the event of December 14 energy of\nsolar protons reached ~600 MeV whereas maximum energy of He was below 100\nMeV/n. The spectra were slightly bended in the lower energy range and preserved\ntheir form during the second event. Difference in the particle flux appearance\nand temporal evolution in these two events may argue for a special conditions\nleading to acceleration of solar particles up to relativistic energies.\n