Cataclysms such as novas, kilonovas, supernova, magnetars, quasars, gamma ray bursts are rarely visible from Earth. Under what conditions (such as distance, day vs. night, naked eye vs. level of optics) would such phenomena be visible from the Earth's surface, and what would they look like in terms of shape, initial duration, brightness, and so forth?
For instance, I have seen questions like how long does a supernova last and I have read that they can be visible for some time afterwards as a nebula forms, but this doesn't tell me what the initial burst would look like. For instance, would it be possible to see a supernova in a neighboring galaxy such as Andromeda? If so, how long would it be visible with the naked eye? Would it look like a flash, last a few seconds, several? I assume with a supernova not in our own galaxy there would be no subsequent light from the expanding shell since it would be too far away, whereas in our own galaxy if it were close enough we would subsequently see it, but in that case would there be a short burst of light, following by darkness and then the re-emergence of light, or would it be a continuously visible phenomena?