hypothetical: "Magnetar" neutron star appears 10 light years from earth.

Do we notice anything different on a day-to-day basis?

If it releases a gamma ray burst like this star did, what does the end of the world look like?

ETA: What if there actually was one there the whole time? Would it have changed how life on earth developed?

I would think life wouldn’t have developed if the Earth was getting blasted by gamma radiation.

Or there would be a marked increase in incidents of “Hulkism”.

I may have read it wrong; my understanding was that there was a constant emission of radiation, but the very powerful burst was much stronger than the usual amount.

The radiation that’s emitted constantly wouldn’t be much of a threat to us from 10 light years away. What’s a concern are the bursts of energy.

Magnetars are only active in this sense for a short time (Wikipedia says 10,000 years) so having one nearby would mean some disastrous extinction-level events in the short-term, but 10,000 years is a blink of an eye in geologic/evolutionary terms. The magnetar wouldn’t be all that different from the extinction of the dinosaurs - a single event that would affect life by wiping out many species and allowing the survivors to fill now-empty niches, but not a long-term selective pressure.