UC Berkeley

Low-mass axionlike particles could be produced in abundance within the cores of hot, compact magnetic white dwarf (MWD) stars from electron bremsstrahlung and converted to detectable x-rays in the strong magnetic fields surrounding these systems. In this work, we constrain the existence of such axions from two dedicated Chandra x-ray observations of ∼40 ks each in the energy range ∼1–10 keV toward the MWDs WD 1859+148 and PG 0945+246. We find no evidence for axions, which constrains the axion-electron times axion-photon coupling to |gaγγgaee|≲1.54×10-25 (3.54×10-25) GeV-1 for PG 0945+246 (WD 1859+148) at 95% confidence for axion masses ma≲10-6 eV. We find an excess of low-energy x-rays between 1 and 3 keV for WD 1859+148 but determine that the spectral morphology is too soft to arise from axions; instead, the soft x-rays may arise from nonthermal emission in the MWD magnetosphere.