# Why the Poisson noise level is set to 2 after applying Leahy norm

• A

## Summary:

Why the Poisson noise level is set to 2 after applying Leahy normalization
I am studying about power spectrum analysis in high energy astrophysics.
I cannot understand why the Poisson noise level is set to 2 after applying Leahy normalization.
$$P_{j}=2 /_{N \mathrm{ph}}\left|a_{j}\right|^{2}$$
The above is the equation for leahy norm, Can I expand the equation from here to require that the Poisson noise level is 2?

Thank you.