History of Whirling Ovation

The Whirling Ovation is a Strand Exotic Rocket Launcher (heavy). Its intrinsic Coronal Culmination is hold-to-charge; charged projectiles carry a delayed Solar payload.

Acquisition

It drops from the final encounter of The Desert Perpetual raid, launched with Edge of Fate. Contest-window completions in the first 48 hours got a guaranteed drop, tied to the triumphs Stop the Clock and Stop the Clock II; afterward it is a random drop.

Catalyst

Per search results, the catalyst (Filled Determination) is farmed from the Epic version of the raid: fully charged shots over-penetrate weaker combatants and cause a delayed Solar detonation with a scorching field. Defeat 500 enemies to unlock. The Game Post (written at launch) said the catalyst was not yet revealed, so this may have come later.