Eisenstein series, p-adic modular functions, and overconvergence

Let p be a prime ≥ 5. We establish explicit rates of overconvergence for some members of the “Eisenstein family”, notably for the p-adic modular function V(E(1,0)∗)/E(1,0)∗ (V the p-adic Frobenius operator) that plays a pivotal role in Coleman’s theory of p-adic families of modular forms. The proof goes via an in-depth analysis of rates of overconvergence of p-adic modular functions of form V(E_k) / E_k where E_k is the classical Eisenstein series of level 1 and weight k divisible by p- 1. Under certain conditions, we extend the latter result to a vast generalization of a theorem of Coleman–Wan regarding the rate of overconvergence of V(E_p-1) / E_p-1. We also comment on previous results in the literature. These include applications of our results for the primes 5 and 7.