Fascinating. (What does it mean?)
Basically, it's telling the engine to render an explosion+fire damage effect when it's determined that a Flame Atronach has died in combat (the explosion does not happen when one despawns). It's essentially a point-blank Fireball, centered on the caster (who in this case is the FA's corpse) and with a large radius, and since it's explosive it could definitely level a small house.