In this paper we find the exact orders of approximation of analytic functions by the complex versions of several potentials (including the Flett potential) generated by the Gamma function and by some singular integrals.
GAL, SORIN G.
"Approximation by complex potentials generated by the Gamma function,"
Turkish Journal of Mathematics: Vol. 35:
3, Article 8.
Available at: https://journals.tubitak.gov.tr/math/vol35/iss3/8