Normally a once-a-century event, these cataclysmic explosion of stars have been witnessed firsthand by Starfleet crews.
One such instance was Beta Niobe in 2269, when members of James Kirk's Enterprise crew were almost trapped on its planet Sarpeidon. Another was a star witnessed by the crew of Jean-Luc Picard's Enterprise. The resulting electro-magnetic pulse of that supernova in 2364 was so feared by the computer-dependent natives of Bynaus in the nearby Beta Magellan system that they commandeered the Enterprise-D as a temporary dump for the planet's computer.
A series of supernovae witnessed by the U.S.S. Voyager crew in the Gamma Quadrant turn out to be the real-time result of "battles" during the Q Continuum's civil war of 2373. They were actually created by spatial disruptions in the Continuum, which created a negative-density false vacuum that sucked nearby matter into the Continuum.