\[\frac{1}{2\pi\mathrm{i}}\int_{-\infty}^{(0+)}e^{tz}t^{-a}U\left(a,b,\ifrac{y}{%
t}\right)\,\mathrm{d}t=\frac{2z^{\frac{1}{2}(2a-b-1)}y^{\frac{1}{2}(1-b)}}{%
\Gamma\left(a\right)\Gamma\left(a-b+1\right)}K_{b-1}\left(2\sqrt{zy}\right),\]