In this paper we characterize possible asymptotics for hitting times in aperiodic ergodic dynamical systems: asymptotics are proved to be the distribution functions of subprobability measures on the line belonging to the functional class
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\[\hspace*{-8mm}\mbox{(A)}\hspace*{6mm}\mathcal{F}=\left\{F\dvtx \mathbb{R}\to [0,1]\dvtx \left\lbrack \matrix{F\mbox{ is increasing, null on }]\!-\!\infty ,0];\hfill \cr\noalign{\vspace*{3pt}}F\mbox{ is continuous and concave;}\hfill \cr\noalign{\vspace*{3pt}}F(t)\le t\mbox{ for }t\ge 0.\hfill}\right.\right\}.\]
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Note that all possible asymptotics are absolutely continuous.