What physical evidence of energetic flares can astronomers detect after the initial burst fades?

Oscillation or "ringing" in the star’s crust

Following a significant, powerful flare event, astronomers can detect residual evidence related to the physical impact of that energy release on the magnetar itself. The vast energy unleashed by the magnetic snap causes mechanical stress, inducing a 'ringing' or oscillation within the star's crust. This oscillation generates a detectable pattern in the subsequent radiation as it fades away, analogous to listening to the sound produced by a bell after it has been struck. Observing this decaying oscillation provides direct insight into the internal structure and immediate mechanical reaction of the magnetar's surface material to the intense magnetic disruption.