Speaker
Description
Coupling of axions or axion-like particles (ALPs) with photons may lead to photons escaping optically opaque regions by oscillating into ALPs. This phenomenon can be probed through the Light Shining through Wall (LSW) technique. While this LSW technique has been used previously in controlled laboratory settings to constrain the ALP-photon coupling ($g_{a\gamma}$), we show that this can also be applied in astrophysical environments. We find that obscured magnetars in particular are excellent candidates for this purpose. A fraction of photons emitted by the magnetar may convert to ALPs in the magnetar neighborhood, escape the large hydrogen column densities, and convert back into photons due to the interstellar magnetic field. Using limits on the observed flux, we can constrain the contribution of this process, and hence constrain $g_{a\gamma}$. The effects of resonant conversion near the magnetar as well as ALP-photon oscillations in the interstellar medium are carefully considered. We find that this can constrain $g_{a\gamma} \le 10^{-10} \; \text{GeV}^{-1}$ for low mass axions ($m_a < 10^{-12}$ eV) with suitable choices of magnetar candidates. The study clearly demonstrates the potential for employing the LSW technique for obscured magnetars for probing and constraining ALP-photon couplings.
