Long-time behaviour for a non-autonomous Klein-Gordon-Zakharov system

The aim of this paper is to study the long-time dynamics of solutions of the evolution system $$\begin{cases} u_{tt} - \Delta u + u + \eta(-\Delta)^{\frac{1}{2}}u_t + a_{\epsilon}(t)(-\Delta)^{\frac{1}{2}}v_t = f(u), & \; (x, t) \in \Omega \times (\tau, \infty), \\ v_{tt} - \Delta v + \eta(-\Delta)^{\frac{1}{2}}v_t - a_{\epsilon}(t)(-\Delta)^{\frac{1}{2}}u_t = 0, & \; (x, t) \in \Omega \times (\tau, \infty), \end{cases}$$ subject to boundary conditions $$u = v = 0, \;\; (x, t)\in \partial\Omega\times (\tau, \infty),$$ where $\Omega$ is a bounded smooth domain in $\mathbb{R}^n$, $n \geq 3$, with the boundary $\partial\Omega$ assumed to be regular enough, $\eta > 0$ is constant, $a_{\epsilon}$ is a H\"older continuous function and $f$ is a dissipative nonlinearity. This problem is a non-autonomous version of the well known Klein-Gordon-Zakharov system. Using the uniform sectorial operators theory, we will show the local and global well-posedness of this problem in $H_0^1(\Omega) \times L^2(\Omega) \times H_0^1(\Omega) \times L^2(\Omega)$. Additionally, we prove existence, regularity and upper semicontinuity of pullback attractors.