e-Science : April 2012 Issue 1
concentrated in a little spot about a half degree wide on the sky. We don’t expect very many from a source, so can you see the problem that pops up? Yes, it’s the background of the neutrinos made in the atmosphere. They look just like the ones we expect from the source. So our sources need to be bright enough to stand out on top of the background. Look at your sky map. Do you see any spots that look more concentrated that the average spot on the sky? How would you really tell? Careful analysis of this sky map shows that there probably aren’t any such spots. If there are real sources in this sky map, they are weak enough that they have added at most a couple of neutrinos at maybe a few random spots in the map. That’s about all we can say with these data. 6. Think about what would happen if there were sources all over the sky but they were individually too weak to stand out. Suppose each of these weak sources left a few neutrinos in IceCube. What would we see? In this case, we’d have a map made up of about equal numbers of neutri- nos, some coming from the atmosphere, the rest from the weak sources. If we just counted, we’d find that there were far more than we expected from the atmosphere (using cosmic ray data, particle interaction theory and computer simulation we have a fairly good idea how many we ex- pect from the atmosphere) and so we would suspect we’d seen something interested just by counting all the events in the map. Unfortunately, this is not the case either, so we are still left to ponder if there are sources in the sky. Since IC40, we have completed the full detector (about twice the size) and it has been running now almost two years. The IceCube scientists are already working on making maps, looking for the hot spots, and counting across the sky, just as you have done. These scientists include students at the University of Adelaide, doing Honours, Masters and PhD level science programs.
July 2012 Issue 2