AI 中文总结
本研究提出利用黑洞X射线双星的热X射线谱探测超轻轴子超辐射云，通过轴子与等离子体费米子的导数耦合加热吸积盘，可得到轴子-电子耦合的约束，灵敏度与XENONnT相当。
AI 中文摘要
作为X射线双星系统一部分的黑洞周围的超轻轴子超辐射云能够加热其吸积盘，并可通过吸积盘发射的热X射线谱探测到这一现象。我们考虑轴子与等离子体费米子的导数耦合，计算轫致辐射逆过程的发射率，该过程会导致吸积盘的温度波动。基于薄盘模型和多色盘模型，我们推导了包含轴子加热的热谱，该谱表现出增强的热光子通量以及红移/蓝移的峰值谱频率。对质量为10倍太阳质量的黑洞X射线双星的热谱进行单峰搜寻以寻找轴子加热特征，若谱测量灵敏度为10%（1%），则对于处于饱和|211⟩态、轴子质量ma=5.2×10^-12 eV的情况，可得到轴子-电子耦合|gae|≳7.5×10^-12（2.4×10^-12）的约束；对于处于饱和|322⟩态、轴子质量ma=1.0×10^-11 eV的情况，可得到|gae|≳4.5×10^-12（1.4×10^-12）的约束。这些预计的灵敏度与XENONnT的灵敏度具有竞争力。详细的连续谱拟合可进一步提高探测能力，并为黑洞自旋减速测量提供互补的约束。
英文摘要
A superradiant cloud of ultralight axions around a black hole, that is part of an X-ray binary system, can heat up its accretion disk and be detected by the thermal X-ray spectrum emitted by the disk. We consider a derivative coupling of the axions to the plasma fermions and calculate the emissivity of the inverse bremsstrahlung process that results in a temperature fluctuation of the disk. Based on the thin-disk model and the multicolor disk model, we derive the thermal spectrum with axion heating, which shows an enhanced thermal photon flux and a red-/blue- shifted peak spectral frequency. A single bump hunting search of the axion heating signature in the thermal spectrum of a $10M_\odot$ black hole X-ray binary with a spectral measurement sensitivity of 10\% (1\%) can derive the constraint on axion-electron coupling $|g_{ae}|\gtrsim7.5\times 10^{-12} ~(2.4 \times 10^{-12})$ for axion mass $m_a=5.2\times 10^{-12}\,$eV in a saturated $|211\rangle$ state, and $|g_{ae}|\gtrsim4.5\times 10^{-12} ~(1.4 \times 10^{-12})$ for axion mass $m_a=1.0\times10^{-11}\,$eV in a saturated $|322\rangle$ state. The projected sensitivities are competitive with those from XENONnT. A detailed continuum fitting can further improve the detectability and provide a complementary bound to the black hole spin-down measurement.
