Teukolsky master equation and Painlev\'e transcendents: numerics and extremal limit

We conduct an analysis of the quasi-normal modes for generic spin perturbations of the Kerr black hole using the isomonodromic method. The strategy consists of solving the Riemann-Hilbert map relating the accessory parameters of the differential equations involved to monodromy properties of the solutions, using the $\tau$-function for the Painlev\'e V transcendent. We show good accordance of the method with the literature for generic rotation parameter $a<M$. In the extremal limit, we determined the dependence of the modes with the black hole temperature and establish that the extremal values of the modes are obtainable from the Painlev\'e V and III transcendents.
Comment: REVTeX 4.2, 17 pages, 7 figures; version 2 with added references and better control of the Stokes phenomenon in the numerical calculations. Results now agree within machine precision to the method of choice when they are both applicable