Black Hole Formation in Fallback Supernova and the Spins of LIGO Sources

Here we investigate within the context of field binary progenitors how the the spin of LIGOsources vary when the helium star-descendent black hole (BH) is formed in a failed supernova(SN) explosion rather than by direct collapse. To this end, we make use of 3d hydrodynamical simulations of fallback supernovain close binary systems with properties designed to emulate LIGOsources. By systematically varying the explosion energy and the binary properties, we are able to explore the effects that the companion has on redistributing the angular momentum of the system. We find that, unlike the mass, the spin of the newly formed BH varies only slightly with the currently theoretically unconstrained energy of the SN and is primarily determined by the initial binary separation. In contrast, variations in the initial binary separation yield sizable changes on the resultant effective spin of the system. This implies that the formation pathways of LIGOsources leading to a particular effective spin might be far less restrictive than the standard direct collapse scenario suggests.