Outflow-driven Transients from the Birth of Binary Black Holes. I. Tidally Locked Secondary Supernovae

Abstract

We propose a new type of electromagnetic transients associated with the birth of binary black holes (BBHs), which may lead to merger events accompanied by gravitational waves in ∼ 0.1 − 1 Gyr. We consider the newborn BBHs formed through the evolution of isolated massive stellar binaries. For a close massive binary, consisting of a primary black hole (BH) and a secondary Wolf-Rayet (WR) star that are orbiting around each other, the spin period of the WR star can be tidally synchronized to its orbital period. Then, the angular momentum of the outer material of the WR star is large enough to form an accretion disk around a newborn, secondary BH, following its core-collapse. This disk may produce an energetic outflow with a kinetic energy of ∼ 10 50 − 10 52 erg and an outflow velocity of ∼ 10 10 cm s −1 , resulting in an optical transient with an absolute magnitude from ∼ −14 to ∼ −17 with a duration of around a day. This type of transient also produces detectable radio signals ∼ 1 − 10 years after the birth of BBHs, via synchrotron emission from non-thermal electrons accelerated at external shocks. The predicted optical transients have a shorter duration than ordinary core-collapse supernovae. Dedicated optical transient surveys can detect them, and distinguish it from ordinary SNe using the different features of its light curve and late-time spectrum. In the paper I, we investigate disk-driven outflows from the secondary BH, whereas possible signals from the primary BH will be discussed in the paper II.

Radio emission from accreting isolated black holes in our galaxy

“…where ζ e ≈ 0.4 (Park et al 2015) is the efficiency of the kinetic energy of protons being transferred to electrons. Hereafter we use the value ζ e = 0.4, as was done in other works that considered radio transients by mildly relativistic outflows (Murase et al 2016;Kimura et al 2017;Kashiyama et al 2018). We note that this estimate on γ min may be inaccurate for outflow velocities much lower than ∼ 0.1c.…”

Radio transients from newborn black holes

“…Interestingly, these are the promising progenitors of BH-BH binaries coalescing within the cosmological timescale Hotokezaka & Piran 2017;Belczynski et al 2017;Kimura et al 2017). In particular, Kimura et al (2017) investigated electromagnetic emissions from disk-driven outflows from a newborn BH formed in such a tidally-locked binary system. Based on the above considerations, the BH formation with a mini-disk may not be rare.…”

“…We take ζ e = 0.4 as fiducial (Park et al 2015). Similar assumptions have been made for studies on outflowdriven radio transients in other contexts (Murase et al 2016;Kimura et al 2017). In the Bohm limit, the shock acceleration timescale of electrons is t acc = (20/3) × cγ e m e c 2 /(eBv 2 ).…”

“…Cooling emission of the ultrafast outflow will be observed as fast luminous blue transients (Kashiyama & Quataert 2015), which might have al- ready been detected (e.g., Drout et al 2014;Tanaka et al 2016). Related UV/optical transients with more kinetic energy have been expected at the birth of double BH binaries, which may lead to GW 150914-like merger events in ∼ 1 − 10 Gyr (Kimura et al 2017). In general, UV/optical transients with a duration of a few days or shorter will be explored more efficiently in the coming years.…”

AT2018lqh: Black Hole Born from a Rotating Star?

“…In this case the accretion is expected to be super-Eddington, and radiation-driven wind is expected to be launched (e.g. Ohsuga et al 2005;Sadowski et al 2014) in addition to the weak mass ejection, which can have a large effect on the observable signatures (e.g., Dexter & Kasen 2013;Kashiyama & Quataert 2015;Kimura et al 2017).…”