  We prove that quasinormal modes (or resonant states) for linear wave
equations in the subextremal Kerr and Kerr-de Sitter spacetimes are real
analytic. The main novelty of this paper is the observation that the
bicharacteristic flow associated to the linear wave equations for quasinormal
modes with respect to a suitable Killing vector field has a stable radial point
source/sink structure rather than merely a generalized normal source/sink
structure. The analyticity then follows by a recent result in the microlocal
analysis of radial points by Galkowski and Zworski. The results can then be
recast with respect to the standard Killing vector field.
