Edit (Turns out I just needed to use Assign to Event rather than bind & UE4 auto-creates an event with the signature. Sweet!) I’ll leave these here as a reference if needed.
onParticleBurst
Name (event name)
Float (emitter time)
Vector (location)
onParticleSpawn
Name (event name)
Float (emitter time)
Vector (Location)
Vector (Velocity)
onParticleDeath
Name (event name)
Float (emitter time)
Integer (Particle time)
Vector (Location)
Vector (Velocity)
Vector (Direction)
onParticleCollide
Name (event name)
Float (emitter time)
Integer (Particle time)
Vector (Location)
Vector (Velocity)
Vector (Direction)
Vector (Normal)
Name (Bone name)
Phys Mat (Material)