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| Main Authors: | , , , , , , , , , |
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| Format: | Preprint |
| Published: |
2025
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2502.08913 |
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Table of Contents:
- Axions are one of the leading dark matter candidates. If we are embedded in a Milky Way dark matter halo comprised of axions, their stimulated decay would enable us to observe a counterimage (``axion gegenschein") with a frequency equal to half the axion mass in the opposite direction of a bright radio source. This spectral line emission will be broadened to $Δν/ν\sim σ_d/c \sim 10^{-3}$ due to the velocity dispersion of dark matter, $σ_d$. In this pilot study, we perform the first search for the expected axion gegenschein image of Vela supernova remnant (SNR) with 26.4 hours of effective ON-OFF data from the Five-hundred-meter Aperture Spherical radio Telescope (FAST) L-band (1.0 - 1.5~GHz) 19-beam receiver. Our null detection limits the axion-photon coupling strength to be $g_{aγγ} \lesssim 2 \times 10^{-10} \mathrm{GeV}^{-1}$ in the mass ranges of $8.7\,μ\mathrm{eV} \leq m_a \leq 9.44\,μ\mathrm{eV}$ and $10.85\,μ\mathrm{eV} \leq m_a \leq 12.01\,μ\mathrm{eV} $. These results provide a stronger constraint on $g_{aγγ}$ in this axion mass range than the current limits obtained by the direct search of axion decay signal from galaxy clusters which uses FAST observations, but is a factor of $\sim 3$ times weaker than the current CAST limit.Based on our observation strategy, data processing methods, and results, the expected sensitivity will reach $\sim 10^{-11}\mathrm{GeV}^{-1}$ with $\sim 2000$ hours of observation in the future.