# Outflow-Driven Transients from the Birth of Binary Black Holes [HEAP]

We consider the electromagnetic radiation from newborn binary black holes (BBHs) formed by the evolution of isolated massive stellar binaries. Before the formation of a BBH, the binary consists of a primary black hole (BH) and a secondary Wolf-Rayet star. We investigate two types of transients from the birth of a secondary BH: one powered by the Bondi-Hoyle-Lyttleton accretion onto the primary BH, and the other induced by accretion onto the secondary BH. In the former scenario, when the secondary collapses to a BH, it may eject a fraction of its outer material, which forms a disk around the primary BH and induces an ultrafast outflow. This companion-induced outflow can lead to week-scale optical transients with a kinetic energy of $\sim10^{47}$ — $3\times10^{48}$~erg, ejecta velocity of $10^8$ — $10^9\rm~cm~s^{-1}$, and absolute magnitude ranging from about $-10$ to $-12$. In the latter scenario, assuming that the tidal torque synchronizes the spin period of the secondary to the orbital period of the primary, the accretion of the stellar material is expected to form a disk around a newborn BH, following its core-collapse. This disk may produce an energetic outflow with a kinetic energy of $\sim10^{52}$~erg and the outflow velocity of $\sim10^{10}\rm~cm~s^{-1}$, resulting in an optical transient of absolute magnitude from $\sim -13$ to $\sim-14$ with a duration of a few days. While dimmer than ordinary supernovae, their light curves and late-time spectra are distinctive, and dedicated optical transient surveys could detect these two types of transients, the second type also leading to detectable radio signals.

S. Kimura and P. Meszaros
Fri, 24 Feb 17
17/50