Why Are Statistical Significance Maps Used in Cosmic Ray Anisotropy Studies?

[vaart]

Dear All,

I have a question regarding the understanding of anisotropy of cosmic rays and how to understand them better. To determine the anisotropy I have seen a lot of papers where they use maps that have a Relative Intensity map and a Statistical significance map of the sky.

I understand the relative intensity map, but I don't understand why the statistical significance maps are used, could some one explain this to me?

Thanks,

caart

 

[Drakkith]

Hmmm... do you happen to have a link to one of the maps?

 

[vaart]

Sure, here is a paper that I have been recently reading.
http://arxiv.org/abs/1105.2326
It's figure 3 at page 15.
At section 3.2, they are explained but I don't really understand it yet, they say that they use the Li and Ma paper:
http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1983ApJ...272..317L&defaultprint=YES&filetype=.pdf

 

[Drakkith]

I'm actually not certain. At first glance I would think that the significance level depends on the intensity of the radiation and the observation time, with a higher significance corresponding to a higher chance that the signal is real and not a background fluctuation, but I'm not sure why the significance level goes into the negative.