Constraining axions with ZTF J1901+1458

The axion-nucleon coupling enables the production of axions through the decay of excited $^{57}\mathrm{Fe}$ nuclei, and axions produced in the Sun through this process are often a target of helioscope searches. We show for the first time that hot, highly magnetic white dwarfs such as ZTF $\mathrm{J}1901+1458$ are a viable target to search for the x-ray signature of axions that were produced by the $^{57}\mathrm{Fe}$ transition in the core and then converted to photons in the magnetosphere. We calculate that a 100 ks observation of ZTF $\mathrm{J}1901+1458$ with NuSTAR would constrain the coupling of axions to nucleons and photons at a level below the bounds of both current and future planned helioscopes.