Symmetry Operators for Maxwell's Equations on Curved Space-Time

We derive necessary and sufficient conditions that a second-order co-variant differential operator be a symmetry operator of Maxwell’s equations in a general curved space-time background. It is found that such operators are naturally formulated in terms of conformal Killing vectors, tensors and spinors. Operators of this type play a role in the solution of Maxwell’s equations via separation of variables in the Kerr background space-time.