Details of the explosion mechanism of core-collapse supernovae ( CCSNe ) are not yet fully understood .
There is an increasing number of numerical examples by ab-initio core-collapse simulations leading to an explosion .
Most , if not all , of the ab-initio core-collapse simulations represent a ‘ slow ’ explosion in which the observed explosion energy ( \sim 10 ^ { 51 } ergs ) is reached in a timescale of \gtrsim 1 second .
It is , however , unclear whether such a slow explosion is consistent with observations .
In this work , by performing nuclear reaction network calculations for a range of the explosion timescale t _ { grow } , from the rapid to slow models , we aim at providing nucleosynthetic diagnostics on the explosion timescale .
We employ one-dimensional hydrodynamic and nucleosynthesis simulations above the proto-neutron star core , by parameterizing the nature of the explosion mechanism by t _ { grow } .
The results are then compared to various observational constraints ; the masses of ^ { 56 } Ni derived for typical CCSNe , the masses of ^ { 57 } Ni and ^ { 44 } Ti observed for SN 1987A , and the abundance patterns observed in extremely metal-poor stars .
We find that these observational constraints are consistent with the ‘ rapid ’ explosion ( t _ { grow } \lesssim 250 ms ) , and especially the best match is found for a nearly instantaneous explosion ( t _ { grow } \lesssim 50 ms ) .
Our finding places a strong constraint on the explosion mechanism ; the slow mechanism ( t _ { grow } \gtrsim 1000 ms ) would not satisfy these constraints , and the ab-inito simulations will need to realize a rapid explosion .