From the article: The pattern [for FRB 180916.J0158+65] begins with a noisy, four-day window, during which the source emits random bursts of radio waves,

From the article: The pattern [for FRB 180916.J0158+65] begins with a noisy, four-day window, during which the source emits random bursts of radio waves, followed by a 12-day period of radio silence. How do astronomers know the bursts are random...? Or is that a shorthand here for lack of understanding about the process (like planets passing in front of the source) and therefore the pattern itself? Edit: formatting