The linked article about the BOAT Biggest Of All Time GRB event is fascinating. https://www.nasa.gov/universe/nasa-missions-study-what-may-be-a-1-in-10000-year

The linked article about the BOAT Biggest Of All Time GRB event is fascinating. https://www.nasa.gov/universe/nasa-missions-study-what-may-be-a-1-in-10000-year-gamma-ray-burst/ https://www.nasa.gov/universe/nasa-missions-study-what-may-b... The graph shows previous events at a few seconds duration, and the Big one at about 1 minute. So immediate effects would be limited to the air and land of half the Earth. Any further effects must be through disrupting Van Allen belt, ozone layer, NO2 in the atmosphere, secondary ionizing radiation products, etc.