[Colorado Doug]

Any supernova producing such a fragment reached our solar system while still glowing would have destroyed our solar system when it exploded.

Maybe it did. We just don't know it yet.

[Pontiac]

The first thing exiting a Supernova is a burst of X-rays that travel at near the speed of light.

A burst of X-rays would from a Supernova that was close enough to send us a rock emitting its own light a would completely sterilize the Earth at least few weeks before the rock got here.

We would be dead long before we had the chance to see that rock in our telescopes.