Which observational signal is primarily anticipated from the final gravitational collapse of a massive magnetar?

Gravitational waves detectable by instruments like LIGO or Virgo

When a magnetar reaches its maximum stable mass and begins the unstoppable implosion toward a singularity, the rapid and violent reshaping and compression of spacetime are expected to generate significant ripples known as gravitational waves. These spacetime distortions might be strong enough to be registered by sensitive detectors such as LIGO or Virgo. Crucially, because the event horizon forms rapidly during this final collapse, the associated electromagnetic output—the flares and radiation typically linked to magnetars—is likely to be truncated or overwhelmed instantly, meaning the gravitational wave signature is the most likely, albeit indirect, evidence of the demise.