Heroic: Algalon and its Normal mode equivalent concludes the Algalon the Observer attunement quest chain, rewarding the . Loren will offer this quest once all four sigils have been turned in to her. The followup quest is the reward for key-bearers who defeat Algalon.
You really did it, <name>. Take the sigils to the Archivum Console and see if you can gain access to the Celestial Planetarium.
You best hurry, <lad/lass>. Time is of the essence.