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excess_error

gammapy.stats.excess_error(n_on, n_off, alpha)

Estimate error on excess for an on-off measurement.

$$\Delta\mu_{excess} = \sqrt{n_{on} + \alpha ^ 2 \times n_{off}}$$

TODO: Implement better error and limit estimates (Li & Ma, Rolke)!

Parameters

n_onarray_like

Observed number of counts in the on region

n_offarray_like

Observed number of counts in the off region

alphaarray_like

On / off region exposure ratio for background events

Returns

excess_errornumpy.ndarray

Excess error estimate

Examples

>>>

>>> excess_error(n_on=10, n_off=20, alpha=0.1)
3.1937438845342623...
>>> excess_error(n_on=4, n_off=9, alpha=0.5)
2.5