The False Alarm Probability (FAP) is a metric to express the significance of a period. For more information see the section on FAPs.

When using the Generalised Lomb-Scargle GLS period analysis method, Peranso not only calculates the GLS statistic (displayed on the Y axis), but also the 1%, 5% and 10% GLS FAP levels. These levels are drawn as dashed lines in the Period Window. The 1% FAP level is marked in red, the 5% level in green and the 10% level in orange. They allow to easily visualize if a period is significant or not. In the below example, one can easily see that the prominent period at 0.06748d is significant, but none of the other smaller 'peaks' pass the FAP criterion in a convincing manner.

Generalised Lomb-Scargle Period Window with 1%, 5% and 10% FAP overlays

This Overlay only exists for Generalised Lomb-Scargle Period Windows.