We present a new analytical approach to derive approximate solutions
describing the shock evolution in non-radiative supernova remnants (SNRs). We
focus on the study of the forward shock and contact discontinuity while
application to the reverse shock is only discussed briefly. The spherical shock
evolution of a SNR in both the interstellar medium with a constant density
profile and a circumstellar medium with a wind density profile is investigated.
We compared our new analytical solution with numerical simulations and found
that a few percent accuracy is achieved. For the evolution of the forward
shock, we also compared our new solution to previous analytical models. In a
uniform ambient medium, the accuracy of our analytical approximation is
comparable to that in Truelove&McKee (1999). In a wind density profile medium,
our solution performs better than that in Micelotta et al. (2016), especially
when the ejecta envelope has a steep density profile. The new solution is
significantly simplified compared to previous analytical models, as it only
depends on the asymptotic behaviors of the remnant during its evolution.Comment: Add discussion for contact discontinuit