Resonant Axion Radiation Conversion in Solar Spicules

Abstract: It has recently been observed that solar spicules covering almost of all solar surface have strong magnetic field $B\sim 10^2$G. They are supposed to be plasma jets emitted from chromosphere and they arrive up to $\sim 10^4$km. Their electron number density is such that $n_e=10^{10}\rm cm^{-3}\sim $$10^{12}\rm cm^{-3}$. Corresponding plasma frequency $m_p=\sqrt{e^2n_e/m_e}$ ( electron mass $m_e$ ) is nearly equal to axion mass $m_a=10^{-5}$eV$\sim 10^{-4}$eV. Thus, resonant radiation conversion of axion with the mass can arise in the spicules. We show that radiations converted from axion dark matter possess flux density $\sim 10^{-6}\mbox{Jy}(m_a/10^{-4}\mbox{eV})(B/3\times 10^2\rm G)^2$. The radiations show line spectrum with frequency $\simeq 24$GHz$(m_a/10^{-4}\rm eV)$. Our estimation has fewer ambiguities in physical parameters than similar estimation in neutron stars because physical parameters like electron number density have been more unambiguously observed in the sun. But, much strong solar thermal radiations would preclude sensitive observations of such radiations from the axions.