Secondary Target and Secondary Attack

Some powers allow you to make secondary (or even tertiary) attacks. A “Hit,” a “Miss,” or an “Effect” entry tells you when to make a secondary attack. Unless otherwise noted, the attack type and the range of a secondary attack are the same as the power’s, and the secondary attack doesn’t require a separate action.
Some powers give you the ability to make a secondary attack at a point later in an encounter, after the initial effect takes place. These powers include information about the secondary attack’s action type, attack type, range, and effect.

Published in Player's Handbook 2, page(s) 219.