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.

 

[pmacias]

Dear caart,

Thank you for your question regarding the use of statistical significance maps in understanding the anisotropy of cosmic rays. It is a valid question and one that is important to address in order to fully understand the research being conducted in this field.

To begin, let's define what we mean by anisotropy. Anisotropy refers to the directional dependence of a physical property, in this case the intensity of cosmic rays. In other words, the intensity of cosmic rays may vary depending on the direction they are coming from. This anisotropy can provide valuable information about the sources and mechanisms of cosmic ray production and propagation.

Now, let's discuss the use of statistical significance maps. These maps are used to determine if the observed anisotropy is statistically significant, meaning that it is not due to chance or random fluctuations in the data. This is important because cosmic rays are subject to various sources of noise and background signals, and it is crucial to differentiate between true anisotropy and random fluctuations.

The statistical significance map is created by comparing the observed cosmic ray intensity at each point in the sky to the expected intensity based on a uniform distribution of cosmic rays. The higher the significance level, the less likely it is that the observed anisotropy is due to chance. This allows researchers to confidently identify regions of the sky with significant anisotropy and investigate potential sources or mechanisms in those regions.

In summary, statistical significance maps are used to confirm the presence of anisotropy in the observed cosmic ray data and to distinguish it from background noise. They are a valuable tool in understanding the anisotropy of cosmic rays and furthering our knowledge of their origins and behavior. I hope this explanation has helped to clarify the use of these maps. Thank you for your interest in this topic.

Best regards,