Electromagnetic Signatures of an Analytical Mini-Disk Model of Supermassive Binary Black Hole Systems*

Supermassive black holes (SMBHs) are thought to be located at the centers of most galactic nuclei. When galaxies merge they form supermassive black hole binary (SMBHB) systems and these central SMBHs will also merge at later times, producing gravitational waves (GWs). Galaxy mergers are gas rich environments and there is likely to be matter surrounding the binary system as well as accreting onto the individual black holes. Therefore, SMBHBs are potential sources of electromagnetic (EM) radiation. The EM signatures depend on gas dynamics, orbital dynamics, and radiation processes. The gas dynamics are governed by general relativistic magnetohydrodynamics in a time-dependent spacetime. Numerically solving the magnetohydrodynamic equation for a time-dependent binary spacetime is computationally expensive. Therefore, it is challenging to conduct a full exploration of the parameter space of these systems and the resulting EM signatures. We have developed an analytical accretion disk model for the mini-disks of a binary black hole system and produced images and light curves using a general relativistic ray-tracing code and a superimposed harmonic binary black hole metric. This analytical model greatly reduces the time and computational resources needed to explore these systems, while incorporating some key information from simulations. We present a parameter space exploration of the SMBHB system in which we have studied the dependence of the electromagnetic signatures on the spins of the black holes, their mass ratio, and their accretion rate. Additionally, we have explored the effects of the fast-light approximation on the images and light curves.