Can I X-Ray a civilisation to death?

Something in orbit around an inhabited planet blasts it with a hefty dose of gamma rays/x-rays/something else, killing everyone within a relatively short time frame (hours or days) but leaving no obvious trace of what has occurred. When offworlders turn up a week later to find out what happened, they find a lot of corpses and not much else.

There is no requirement to kill everything single living thing, just enough members of enough species that the ecosystem and any extant civilisation collapses.

What form of radiant energy, if any, could achieve this effect?

some considerations

I was going to use gamma rays, but am concerned they wouldn't penetrate an Earth-like atmosphere. Or would the proximity and intensity make that not a problem? e.g. could an intense enough burst destroy the atmosphere so quickly that the hard radiation can then kill people directly?

When it comes to traces left behind by the blast, am I right in thinking that there wouldn't be residual radioactivity? Or would an intense enough burst of gamma or x-ray cause alpha/beta decay in materials on the planet's surface? (For the purposes of running scans to figure out what happened.)

posted over 5 years ago

propaganamede‭

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