Energy Spectrum of Shock-Accelerated Particles.

We have quantified the injection rate of low-energy particles (90-1000 keV) at the front of three interplanetary shocks detected by ISEE-3 spacecraft. We have used a MHD code to simulate the shock propagation and the focused-diffusion equation for particle propagation. This allows us to quantify the injection rate of particles, Q, at the shock by fitting the observed flux and anisotropy at different energies. We relate the variations of the efficiency of the particle acceleration with the interplanetary magnetic field and plasma conditions in the shock front region magnetically connected with the observer. Particularly, with the MHD strength of the shock, the interplanetary magnetic field-shock normal angle, the extent of the shock, and the heliolongitude of the parent solar activity that generates the shock.