  Recently, several measurements of the nuclear spin lattice relaxation rate
$T_{1}^{-1}$ in the newly discovered superconducting Fe-pnictides have been
reported. These measurements generally show no coherence peak below $T_{c}$ and
indicate a low temperature power law behavior, the characteristics commonly
taken as evidence of unconventional superconductivity with lines of nodes
crossing the Fermi surface. In this work we show that (i) the lack of a
coherence peak is fully consistent with the previously proposed nodeless
extended $s_{\pm}$-wave symmetry of the order parameter (whether in the clean
or dirty limit) and (ii) the low temperature power law behavior can be also
explained in the framework of the same model, but requires going beyond the
Born model.

Superconductivity;Strongly Correlated Electrons