On the size distribution of supernova remnants in the Magellanic Clouds

Understand

The physical sizes of supernova remnants (SNRs) in a number of nearby galaxies follow an approximately linear cumulative distribution, contrary to what is expected for decelerating shock fronts.

• This has been attributed to selection effects, or to a majority of SNRs propagating in "free expansion", at constant velocity, into a tenuous ambient medium.
• We compile a list of 77 known SNRs in the Magellanic Clouds (MCs), and argue that they are a fairly complete record of the SNe that have exploded over the last ~20kyr, with most now in the adiabatic, Sedov phase of their expansions.
• The roughly linear cumulative size distribution (uniform in a differential distribution) can result from the combination of a deceleration during this phase, a transition to a radiation-loss-dominated phase at a radius that depends on the local gas density, and a distribution of ambient densities varying roughly as rho^{-1}.