Random angular momentum in convection: delayed explosions of red supergiants following failed supernovae

When collapse of the iron core in a massive red or yellow supergiant does not lead to a neutrino-driven supernova explosion, a significant fraction of the convective hydrogen envelope will fall in towards the black hole formed from the collapsing core. I will show that, even in non-rotating supergiants, the random velocity field in the convective envelope alone results in significant specific angular momentum in each infalling shell. Using 3D hydrodynamical simulations, I will show that infall of the convective envelope leads to nearly complete envelope ejection in an explosion with an energy of 10⁴⁸ ergs and with outflow speeds of hundreds of km/s. The lightcurve of such an event would exhibit a characteristic, red plateau with a luminosity of 10⁴⁰ ergs/s and a duration of several hundred days. These events would appear quite similar to luminous red novae with red or yellow supergiant progenitors.