Inverse problem for subdiffusion equation with fractional Caputo derivative

We consider an inverse problem on determining the right-hand side of the subdiffusion equation with the fractional Caputo derivative. The right-hand side of the equation has the form $f(x)g(t)$ and the unknown is the function $f(x)$. The condition $u (x,t_0)= \psi (x)$ is taken as the over-determination condition, where $t_0$ is some interior point of the considered domain and $\psi (x)$ is a given function. By the Fourier method we show that under certain conditions on the functions $g(t)$ and $\psi (x)$ the solution of the inverse problem exists and is unique. We provide an example showing the violation of the uniqueness of the solution of the inverse problem for some sign-changing functions $g(t)$. For such functions $g(t)$ we find necessary and sufficient conditions on the initial function and on the function from the over-determination condition, which ensure the existence of a solution to the inverse problem.