Distinguishing Time Clustering of Astrophysical Bursts

Astrophysical burst events such as fast radio bursts and some gamma ray events can repeat -- periodically, without a clear pattern, clustered in time, or with activity occurring in periodic windows. We focus here on periodic windowed behavior, demonstrating methods for identifying it and characterizing it. Predictability of activity offers the opportunity to observe counterpart emission in other wavelengths and learn about the burst astrophysics. An important aspect is accounting for the "curious incident of the dog in the night time" -- lack of bursts carries information. We analyze six years of data from the soft gamma repeater SGR1935+2154 as a worked example, deriving a period of 231 days and 55\% duty cycle.