Abstract
Axion as one of the promising dark matter candidates can be detected through narrow radio lines emitted from the magnetic white dwarf stars. Due to the existence of the strong magnetic field, the axion may resonantly convert into the radio photon (Primakoff effect) when it passes through a narrow region in the corona of the magnetic white dwarf, where the plasma frequency is equal to the axion mass. We show that for the magnetic white dwarf WD 2010+310, the future experiment SKA phase 1 with 100 hours of observation can effectively probe the parameter space of the axion-photon coupling $g_{a\gamma}$ up to $\sim 10^{-12}~ \text{GeV}^{-1}$ for the axion mass range of $0.2 \sim 3.7~ \mu$eV. Note that in the low mass region ($m_a \lesssim 1.5 ~\mu\text{eV}$), the WD 2010+310 could give greater sensitivity than the neutron star RX J0806.4-4123.
Highlights
The existence of dark matter (DM) has been established by solid astrophysical and cosmological observations [1,2]
Due to the existence of the strong magnetic field, the axion may resonantly convert into the radio photon (Primakoff effect) when it passes through a narrow region in the corona of the magnetic white dwarf, where the plasma frequency is equal to the axion mass
In this work we focus on the signals of axion DM from magnetic white dwarf stars (MWDs) whose magnetic fields are at order of 107 ∼ 108 G
Summary
The existence of dark matter (DM) has been established by solid astrophysical and cosmological observations [1,2]. Based on the possible couplings between axion and the electromagnetic sector, a number of experiments have been set up to search for axion DM signals These interactions predict two different phenomena: (1) the conversion between an axion particle and a photon under magnetic fields (so-called Primakoff effect [20]), e.g., axion helioscope [21,22], “light shining through a wall” experiments [23,24], and so on; (2) the photon birefringence under axion background [25,26,27,28,29,30]. In this work we focus on the signals of axion DM from MWDs whose magnetic fields are at order of 107 ∼ 108 G.
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