Only if you are in a hurry, say an advanced civilization has been around for 1M years (0.07% faster than us). It might well be worth sending out millions of drones to the most promising areas at 1% of the speed of light, their advanced sensors and telescopes and science would likely be able to pick the most likely stars based on metal content, vicinity (i.e. stable of 1B years), water, temp, etc.

Not to mention they could send probes closer and further from the galactic center to take advantage of the slower and faster rotation rate to see new stars.

As for the nuclear fission blast I have my doubts. Ham radio folks brag about 1000 miles a watt, in a lossy atmosphere and multiple bounces that reflect less than 1% for each bounce. Using advanced things like tubes of transistors and a copper cable thrown over a tree branch.

Using the 1 watt per 1000 miles the largest nuclear explosion would be 22 light years, and clear line of sight through space is going to transmit quite a bit better than bouncing off the atmosphere then off the ground several times.

An advanced civilization could make say a square km array (which us lowly humans have managed) and would understand nuclear bombs enough to know their likely signature, decay rate, shape of the curve, etc. Much like how astronomers use supernovas as standard candles for distance, despite crazy different red shifts.

Seems quite reasonable for a civilization to keep track of anything going on in their fraction of the galaxy.

"People for some reason refuse to comprehend just how hard is it to send a speck of dust over light years of distance" It's only hard if you are in a hurry, in fact we have 3 rocks come through our solar system from well more than a light year away.