Generalized wave polynomials and transmutations related to perturbed   Bessel equations
  The transmutation (transformation) operator associated with the perturbed Bessel equation is considered. It is shown that its integral kernel can be uniformly approximated by linear combinations of constructed here generalized wave polynomials, solutions of a singular hyperbolic partial differential equation arising in relation with the transmutation kernel. As a corollary of this results an approximation of the regular solution of the perturbed Bessel equation is proposed with corresponding estimates independent of the spectral parameter. 
Vladislav V. Kravchenko, Sergii M. Torba, Jessica Yu. Santana-Bejarano
math.CA math.AP math.NA