On the $\nu$-zeros of the Bessel functions of purely imaginary order

Abstract

The $\nu$-zeros of the Bessel functions of purely imaginary order are examined for fixed argument $x>0$. In the case of the modified Bessel function of the second kind $K_{i\nu}(x)$, it is known that it possesses a countably infinite sequence of real $\nu$-zeros described by $\nu_n\sim \pi n/\log\,n$ as $n\to\infty$. Here we apply a unified approach to determine asymptotic estimates of the $\nu$-zeros of the modified Bessel functions $L_{i\nu}(x)\equiv I_{i\nu}(x)+I_{-i\nu}(x)$ and $K_{i\nu}(x)$ and the ordinary Bessel functions $J_{i\nu}(x)\pm J_{-i\nu}(x)$.