On extreme transient events from rotating black holes and their gravitational wave emission

Abstract

The super-luminous object ASASSN-15lh (SN2015L) is an extreme event with a total energy E<SUB>rad</SUB> ≃ 1.1 × 10<SUP>52</SUP> erg in blackbody radiation on par with its kinetic energy E<SUB>k</SUB> in ejecta and a late time plateau in the UV, which defies a nuclear origin. It likely presents a new explosion mechanism for hydrogen-deprived supernovae. With no radio emission and no H-rich environment, we propose to identify E<SUB>rad</SUB> with dissipation of a baryon-poor outflow in the optically thick remnant stellar envelope produced by a central engine. By negligible time-scales of light crossing and radiative cooling of the envelope, SN2015L's light curve closely tracks the evolution of this engine. We here model its light curve by the evolution of black hole spin during angular momentum loss in Alvén waves to matter at the Inner Most Stable Circular Orbit (ISCO). The duration is determined by σ = M<SUB>T</SUB>/M of the torus mass M<SUB>T</SUB> around the black hole of mass M: σ ∼ 10<SUP>-7</SUP> and σ ∼ 10<SUP>-2</SUP> for SN2015L and, respectively, a long GRB. The observed electromagnetic radiation herein represents a minor output of the rotational energy E<SUB>rot</SUB> of the black hole, while most is radiated unseen in gravitational radiation. This model explains the high-mass slow-spin binary progenitor of GWB150914, as the remnant of two CC-SNe in an intra-day binary of two massive stars. This model rigorously predicts a change in magnitude ∆m ≃ 1.15 in the light curve post-peak, in agreement with the light curve of SN2015L with no fine-tuning.