NOT A TEACHER
The meaning of the A- prefix in the words that you gave (awake, arouse) emphasizes that the action happened only once, that it's a one-time action. The use of A- is similar to the adverbial particle "up" that is used nowadays instead. Mind you, you can't use the prefix A- to form a new phrase, while you can do this with "up".
This is only one of the meanings of the A- prefix. It's a much more complex topic, but I hope I answered what you wanted to know.
Student or Learner