  Muon spin relaxation experiments have been performed in the pyrochlore
iridate Pr_2Ir_2O_7 for temperatures in the range 0.025-250 K. Kubo-Toyabe
relaxation functions are observed up to > 200 K, indicating static magnetism
over this temperature range. The T -> 0 static muon spin relaxation rate
Delta(0) ~ 8 mus^-1 implies a weak quasistatic moment (~0.1 mu_B). The
temperature dependence of Delta is highly non-mean-field-like, decreasing
smoothly by orders of magnitude but remaining nonzero below ~150 K. The data
rule out ordering of the full Pr^3+ CEF ground-state moment (3.0 mu_B) down to
0.025 K. The weak static magnetism is most likely due to hyperfine-enhanced
^141Pr nuclear magnetism. The dynamic relaxation rate lambda increases markedly
below ~20 K, probably due to slowing down of spin fluctuations in the
spin-liquid state. At low temperatures lambda is strong and
temperature-independent, indicative of a high density of low-lying spin
excitations as is common in frustrated antiferromagnets.
