We explore the analogy between a rotating magnetized black hole and an axisymmetric pulsar and derive its electromagnetic spindown after its formation in the core collapse of a supermassive star. The spindown shows two characteristic phases, an early Blandford-Znajek phase that lasts a few hundred seconds, and a late Kerr-Newman afterglow phase that lasts much longer. During the first phase, the spindown luminosity decreases almost exponentially, whereas during the afterglow phase it decreases as t^-4/3. We associate our findings with long duration gamma-ray bursts (GRB) and compare with observations.
Date added: Mon, 21 Oct 13