Delay in onset times of solar energetic particles

Onset analysis is a commonly used method in studying Solar Energetic Particles (SEPs). One can use the linear dispersion relation between the onset time and the reciprocal of particle speed to determine the length of the connecting magnetic field line or time of injection. This is true if the SEP have travelled nearly scatter free at nearly zero pitch angle along the path it travelled. It is important to determine the the time of injection and location of the SEP release at the Sun. Using a particle transport model we study the effect of scattering in the determination of SEP onsets. Using different levels of scattering we find the delays of energetic particles as they arrive at Earth. These delays will affect the correct determination of time of injection and distance travelled.