So we know that many people are putting hard constraints on the galactic habitability zone based on the presence of nearby supernova/gamma ray bursts. But if they only affect the ozone layer, then I doubt that it's as hard of a constraint as many people think it is.
For one thing - there is practically no ozone layer around the planets of red dwarfs (and possibly even low-mass K-stars like Epsilon Eridani and Alpha Centauri B - IMHO, K-stars offer the best prospects for life on other planets.)
With this information, I am wondering wondering about the outcome, particularly in regard to life: would a nearby supernova really do so much damage to planets around those stars?
For instance, would a supernova really cause more damage than, say, the K/T extinction event 65 million years ago? Also, given that much marine life is shielded from UV rays by layers or ocean water, is it really going to cause significant amounts of damage to such life in that environment?
As a side note, maybe this about surviving gamma ray bursts is relevant for complex life too (although this response might be imperfect for now.)