The Galois image of twisted Carlitz modules

We determine the defect def(Δ,N)def(Δ,N), i.e., the deviation from surjectivity of the attached Galois representation, and the degree f(Δ,N)f(Δ,N) of the constant field extension in the N  -th torsion field of the twisted Carlitz module with discriminant Δ, where Δ,N∈A=Fq[T]Δ,N∈A=Fq[T].