Gamma Ray Burst's and Earth's Atmo

[steevey]

Ok, so I had two different sources which conflict with each other about what a gamma ray burst would do at what range. One source which recently recorded a gamma ray burst and said "if it were aimed at us..." which seems weird to begin with, but it was also not even in our galaxy, and they said it would stop photosynthesis and damage the Earth's atmosphere, particularly the ozone. Then I found some other sources which said that if a gamma ray burst occurred within 3,000 light years of us, it would severely damage the atmosphere and do things like cause photosynthesis to cease, and at a distance from the center of the galaxy or more, it would only do a very small amount of damage to the atmosphere. I don't really get why it would say "aimed at us" because that's clearly only jets from something a quasar or pulsar that would really require aim, a gamma ray burst is radial. but the jet's from a quasar alone would fry us, there wouldn't need to be a gamma ray burst from it.

[Arch2008]

Well a GRB does have opposing jets like a pulsar, so it would do the most damage if “aimed at us”. Usually, it must be within 1000 light years to cause extinction type damage, too, but I suppose that would be dependent on how energetic it is.

http://www.nasa.gov/mission_pages/GLAST/news/high_grb.html