It's a verb: https://how-to-all.com/%D0%BC%D0%BE%...81%D0%BB%D0%B0
Он погас
Она погасла
Оно погасло
Они/мы/вы погасли
It's all about past time.
It's meaning differs from "гасить/погасить" as if -ться is implied, that is "self-applied-action". Человек погасил костёр. Костёр погас.
It's like perfect+past form of verb "погасать":
https://ru.wiktionary.org/wiki/%D0%B...B0%D1%82%D1%8C
It seems to me it has no own form for present or future times.