A GfsParticle is basically an inert Lagrangian particle. It can be used as a particle type to define a list of Lagrangian particles (GfsParticleList). Each GfsParticle is characterised by its id number (interger) and position (X,Y,Z).
The GfsParticle particle object is derived from GfsEvent but does not inherit of its read/write method i.e. timing (start, end ...) cannot be specified directly for a GfsParticle but has to be specify for the whole GfsParticleList.