Title: A 3.55 keV Photon Line and its Morphology from a 3.55 keV ALP Line Show Chinese title

Title: 一个3.55 keV光子线及其从一个3.55 keV ALP线的形态

Abstract: Galaxy clusters can efficiently convert axion-like particles (ALPs) to photons. We propose that the recently claimed detection of a 3.55--3.57 keV line in the stacked spectra of a large number of galaxy clusters and the Andromeda galaxy may originate from the decay of either a scalar or fermionic $7.1$ keV dark matter species into an axion-like particle (ALP) of mass $m_{a} \lesssim 6\cdot 10^{-11}~{\rm eV}$, which subsequently converts to a photon in the cluster magnetic field. In contrast to models in which the photon line arises directly from dark matter decay or annihilation, this can explain the anomalous line strength in the Perseus cluster. As axion-photon conversion scales as $B^2$ and cool core clusters have high central magnetic fields, this model can also explains the observed peaking of the line emission in the cool cores of the Perseus, Ophiuchus and Centaurus clusters, as opposed to the much larger dark matter halos. We describe distinctive predictions of this scenario for future observations. Show Chinese abstract

Abstract: 星系团可以有效地将类轴子粒子（ALPs）转换为光子。 我们提出，最近在大量星系团和仙女座星系的叠加光谱中声称检测到的3.55--3.57 keV线可能源自标量或费米子$7.1$keV暗物质粒子衰变为质量为$m_{a} \lesssim 6\cdot 10^{-11}~{\rm eV}$的类轴子粒子（ALP），随后在星系团磁场中转换为光子。 与光子线直接来自暗物质衰变或湮灭的模型不同，这可以解释Perseus星系团中的异常线强度。 由于轴子-光子转换随$B^2$而变化，而冷核心星系团具有高的中心磁场，因此该模型也可以解释在Perseus、Ophiuchus和Centaurus星系团的冷核心中观测到的线发射峰值，而不是更大的暗物质晕。 我们描述了这一情景对未来观测的独特预测。