Characteristic signatures in the thermal emission from accreting binary black holes

Abstract

We present the results of a calculation of the thermal spectrum from a 2D, moving mesh, high-accuracy, viscous hydrodynamical simulation of an accreting supermassive black hole (SMBHs) binary. We include viscous heating, shock heating, and radiative cooling, evolving for longer than a viscous time so that we reach a quasi-steady accretion state. In agreement with previous work, we find that gas is efficiently stripped from the inner edge of the circumbinary disc and enters the cavity along accretion streams, which feed persistent 'minidiscs' surrounding each black hole.We also find that emission from the shock-heated minidiscs and accretion streams prevents any deficit in high-energy emission that may be expected inside the circumbinary cavity, and instead leads to a characteristic brightening of the spectrum beginning in soft X-rays.