In association with the large solar flare of April 15th 2001, the Chacaltaya neutron monitor observed an 8.2 sigma enhancement of the counting rate between 13:51 and 14:24 UT. Since the enhancement was observed from 11 minutes before the GLE, solar neutrons must be involved in this enhancement. 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 another magnetic loop, particles inside the loop may be accelerated by the collision process within a few minutes. This may be an origin of solar cosmic rays.

On April 15, 2001, a large solar flare was observed near the west limb of the Sun (the `Easter flare'). In association with this flare solar neutrons were observed by the Chacaltaya neutron monitor. They were produced contemporaneously with the gamma-ray lines at 13:45-13:51UT. We conclude that protons were accelerated during this period. Soft X-ray images of the flare by the Yohkoh satellite indicate that proton acceleration probably occurred when the foot of a magnetic loop collided with the other magnetic loop. Plasma particles inside the loop may be accelerated by a shock acceleration process, in which plasma particles attain high energies in a few minutes by interacting with high-speed wind.

Proceedings of the 30th International Cosmic Ray Conference; Rogelio Caballero, Juan Carlos D'Olivo, Gustavo Medina-Tanco, Lukas Nellen, Federico A. Sánchez, José F. Valdés-Galicia (eds.); Universidad Nacional Autónoma de México, Mexico City, Mexico, 2008; Vol. 1 (SH), pages 29-32