Search for Axionic Dark Matter Using the Magnetar PSR J1745-2900.

We report on a search for dark matter axion conversion photons from the magnetosphere of the Galactic Center magnetar PSR J1745-2900 using spectra obtained from the Karl G. Jansky Very Large Array (the National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.). No significant spectral features are detected. Using a hybrid model for PSR J1745-2900 and canonical assumptions about the dark matter density profile, we exclude axion models with axion-photon coupling g_{aγγ}>6-34×10^{-12}  GeV^{-1} with 95% confidence over the mass ranges 4.2-8.4, 18.6-26.9, 33.0-41.4, 53.7-62.1, and 126.0-159.3  μeV. If there is a dark matter cusp, the limits reduce to g_{aγγ}>6-34×10^{-14}  GeV^{-1}, which overlap some axion models for the observed mass ranges >33  μeV. These limits may be improved by modeling the stimulated emission that can boost the axion-photon conversion process.