Well, there are many anti-hawk measures that other people have more knowledge with and will advise you on - devices you can use, fence you can put over the coop, etc, but I'm going to go out on a limb and ask: do you have any ravens or crows nearby? Believe it or not, it's the ravens that keep the hawks away for me, as they are very territorial and will chase away any hawks. If so, you could lure ravens or crows over by putting out scraps for them.
Just a thought, anyways...for now, keep your chickens in a safe area unless you're supervising them, at any rate.