  Source imaging methodology is used to provide a three-dimensional two-pion
source function for mid-rapidity pion pairs with $p_T<70$ MeV/c in central
($0-7%$) Pb+Pb collisions at $\sqrt s_{NN}$=17.3 GeV. Prominent non-Gaussian
tails are observed in the pion pair transverse momentum (outward) and in the
beam (longitudinal) directions. Model calculations reproduce them with the
assumption of Bjorken longitudinal boost invariance and transverse flow
blast-wave dynamics coupled with "outside-in burning" in the transverse
direction; they also yield a proper time for breakup and emission duration for
the pion source.
