  Using a simplified model for the hadronic emission from young supernova
remnants (SNRs), we derive an expression to calculate the hadronic luminosity
with time, depending on the SN ejecta density profile and the density structure
of the surrounding medium. Our analysis shows that the hadronic emission will
decrease with time for core-collapse SNe expanding in the winds of their
progenitor stars, but increase with time for SNe expanding into a constant
density medium, typical of Type Ia SNe. Using our expressions, we can compute
the time-dependent hadronic flux from some well-known young SNe and SNRs with
time, and where applicable reproduce previous results in the appropriate
parameter regime. Using our calculations, we also emphasize the exciting
possibility that SN 1987A may become a visible gamma-ray source in the next
decade.
