Ramanujan congruences and étale cohomology

Question

What is a good reference for the story of congruences such as

$$\displaystyle \tau(n) \equiv \sigma(11)(n) \mod\ 691$$

with a conceptual explanation with connections to étale cohomology, etc?

Answer 1

The paper of Swinnerton-Dyer in Lecture Notes in Math 350, as well as Serre's Bourbaki talk on the same topic.

Answer 2

The paper of Deligne, Formes modulaires et représentations $l$-adiques, available at numdam, has these things.