After the bounty is completed once, it becomes available as a repeatable daily quest, offering small amounts of cash and experience, as well as 40 renown with one of the Factions and some give marks or other rewards. It is recommended to find a full group for each one as these fights are as tough as alert bosses. It is possible to swarm the targets with any number of players and they will all gain credit towards their bounty as long as they have participated for most of the fight.
All bounty missions rewards the player with experience, some cash, and one piece of unique equipment. Note that the equipment is only rewarded for the first completion. Afterwards, only cash and experience would be given.