Possible Duplicate:
Automorphisms of projective special linear group
I'm sure this is well known, but I don't know where to look up such things.
What is $\operatorname{Aut}(\operatorname{PSL}_2(\mathbb{F}_q))$ for $q$ a power of a prime? More important to me than what the automorphisms are is what the isomorphism class of $\operatorname{Aut}(\operatorname{PSL}_2(\mathbb{F}_q))$ is.