New constraints on the axion-photon coupling constant for solar axions

Resonance excitation of the $^{83}$Kr first nuclear level ($E = 9.4$ keV) by solar axions formed via the Primakoff mechanism is sought. The $\gamma$- and X-ray photons and the conversion and Auger electrons arising from the excited-level relaxation are detected with a gas proportional counter of a low-background detector in the underground Baksan Neutrino Observatory. The following experimental constraint is obtained for the product of the axion-photon coupling constant and the axion mass:$|g_{A\gamma}\times m_A|\leq 6.3\times10^{-17}$. In the framework of the hadronic-axion model, this corresponds to a new axion-mass constraint of $m_A \leq 12.7$ eV at $95\,\%$ C.L.