When can we ignore the delta function in th Feynman rules?

[Vereinsamt]

in peskin-schroeder and http://www.hep.phy.cam.ac.uk/batley/particles/handout_04.pdf" the amplitude for $$e^-e^+\rightarrow \mu^- \mu^+$$ is written using feynman rules as follows
$$-iM=[\bar{v}(p_2)(-ie\gamma^\mu )u(p_1)] \frac{-ig_{\mu\nu}}{q^2}[\bar{u}(k_1)(-ie\gamma^\nu )v(k_2)]$$

but what about the delta function integeration? is it already done here?

thanks in advanced!

 

[SporadicSmile]

I may well be wrong here, but that looks like the M matrix part of the S matrix, and it is the S matrix that has the delta function in it, so you shouldn't be expecting a delta function.

again i DID only just do this, so i may be wrong.