Calculating Electromagnetic Signatures of Binary Black Hole Systems

Supermassive black hole binary (SMBHB) systems are potential sources of electromagnetic (EM) radiation, with the EM signatures influenced by gas dynamics, orbital dynamics, and radiation processes. The gas dynamics are governed by general relativistic magnetohydrodynamics (GRMHD) in a time-dependent spacetime. However, numerically solving the GRMHD equations for such a binary system is computationally expensive, making it difficult to fully explore the parameter space and resulting EM signatures. To address this, we have developed an analytical accretion disk model for the mini-disks in a binary black hole system, producing images and light curves using a general relativistic ray-tracing code combined with a superimposed harmonic binary black hole metric. This model significantly reduces the computational cost, while incorporating key features from simulations. We will present recent improvements, including a new analytical spacetime that describes the system from inspiral to merger, along with time-varying mini-disk accretion rates derived from GRMHD simulations. Furthermore, we have investigated the effects of the fast-light approximation on the EM signals and evaluated its validity in ray-tracing and radiative transport codes. Additionally, we will present progress in calculating EM signals using GRMHD simulations of inspiraling and merging SMBHB systems, which will inform future refinements of the analytical disk model.