30TH INTERNATIONAL COSMIC RAY CONFERENCE Simultaneous Detection of High-Energy Solar Neutrons and Protons at Chacaltaya

Abstract: In association with the large solar flare of April 15th 2001, the Chacaltaya neutron monitor observed an 8.2σenhancement of the counting rate between 13:51 and 14:24 UT. Since the en-hancement was observed from 11 minutes before the GLE, solar neutrons must be involved in this enhancement. The differential energy spectrum of solar neutrons can be expressed by a simple power law in energy with the index γ = －4.0±1.0. On the other hand, an integral energy spectrum of solar protons has been obtained in the energy range between 650 MeV and 12 GeV. The spectrum can also be expressed by a power law with the power index γ=－2.75±0.15. The flux of solar protons ob-served at Chacaltaya (at ≧12 GeV) was already one order less than the flux of the galactic cosmic rays. It may be the first time to have the energy spectra of both high energy protons and neutrons si-multaneously. Comparing with the Yohkoh Soft X-ray Telescope images with the observed particle time profiles, we can draw a picture on the particle acceleration mechanism as follows. By the loop-loop collisions, high speed plasma wind is generated. When the high speed plasma hits at the top of a magnetic loop, particles inside the loop may be accelerated by the collision process within a few mi-nutes. This may be an origin of solar cosmic rays. The solar neutron event observed by the Cha