[Cosmo-torun] looking for hints on velocity distribution of electrons in relativistic jets

Hi everybody, I'm interested if anybody has some quick nice references or ideas regarding - as in the subject - what the velocities in relativistic jets can be - what this can depend on from theoretical considerations/modelling? The bottom line is, can we have some constrainst on these velocities from models, or models and ovservations (if so - what observables are needed) and what this can depend on ? Is it very bad to assume that these can span from say some arbitrary value to one in \beta space with flat statistical distribution ? Can we have some hints on this distribution ? Motyl, I could use your help here ? I don't have time for getting through tons of papers. Bartek