What is the affective correlate to catharsis? Sylvan Tomkins could point the way to an answer. He distinguishes sharply between two basic positive affects: excitement and joy. Excitement is the affect that drives alertness and effort. It is worth it to work on something because the affect of excitement has been awakened to some degree. Without excitement there would be no attention.
After excitement - or after any of the negative affects, any state with a high density of neural firing, if there is a sudden change in neural firing, humans experience joy, and they smile. Depending on the situation, the joy could be interpreted as relief, triumph, recognition - a number of different outcomes. But the key for triggering joy is a combination of two variables: the density of stimulation must have initially been quite high, and the reduction in density must be sudden. So a sudden reduction in a density that was already relatively low will not produce joy, nor will a gradual reduction of high density.
One could suppose that joy is the affect involved in catharsis, no matter what type of truth is is attached to. A discovery, an answer, a relief - whether a unified theory or a psychoanalytic insight