Constraining the axion mass through gamma-ray observations of pulsars
Constraining the axion mass through gamma-ray observations of pulsars
复制标题
DOI：
10.1103/physrevd.100.063005
复制
发表时间：
2019-08
影响因子：
5
通讯作者：
S. Lloyd;P. Chadwick;A. Brown
中科院分区：
文献类型：
--
作者：
S. Lloyd;P. Chadwick;A. Brown
我们分析了在60 $-$ 500 MeV范围内9年的PASS 8 $\textit{Fermi}$ -LAT数据，并确定了17颗伽玛射线暗脉冲星的通量上限（UL），作为脉冲星核心核子-核子轫致辐射产生轴子的探针。利用先前发表的脉冲星轴子衰变伽马射线光子通量模型，该模型依赖于20 MeV的高核心温度，我们改进了UL轴子质量（$m_a$）的测定，在95％的置信水平下，达到9.6 $\times$ 10 $^{-3}$ eV，比以前的结果提高了8倍。我们表明，在实际较低的脉冲星核心温度为4兆电子伏或更低时，轴子发射率（每体积的能量损失率）降低到这样的程度，以至于轴子发射率和伽马射线信号变得可以忽略不计。我们考虑了一种基于每质量能量损失率的替代发射模型，以使$m_a$受到$Fermi$ -LAT观测的约束。对于脉冲星核心温度$<$ 0.1 MeV，该模型得出了一个合理的UL $m_a$为10 $^{-6}$ eV，但需要了解脉冲星$B$场中轴子到光子转换的程度，才能精确地确定UL轴子的质量。轴子通量的峰值很可能产生$\leq$ 1 MeV能量范围内的伽马射线，因此未来中能量伽马射线任务的观测，如AMEGO和e-ASTROGAM，将对进一步限制UL $m_a$至关重要。
We analyze 9 years of PASS 8 $\textit{Fermi}$-LAT data in the 60$-$500 MeV range and determine flux upper limits (UL) for 17 gamma-ray dark pulsars as a probe of axions produced by nucleon-nucleon Bremsstrahlung in the pulsar core. Using a previously published axion decay gamma-ray photon flux model for pulsars which relies on a high core temperature of 20 MeV, we improve the determination of the UL axion mass ($m_a$), at 95 percent confidence level, to 9.6 $\times$ 10$^{-3}$ eV, which is a factor of 8 improvement on previous results. We show that the axion emissivity (energy loss rate per volume) at realistic lower pulsar core temperatures of 4 MeV or less is reduced to such an extent that axion emissivity and the gamma-ray signal becomes negligible. We consider an alternative emission model based on energy loss rate per mass to allow $m_a$ to be constrained with $Fermi$-LAT observations. This model yields a plausible UL $m_a$ of 10$^{-6}$ eV for pulsar core temperature $<$ 0.1 MeV but knowledge of the extent of axion to photon conversion in the pulsar $B$ field would be required to make a precise UL axion mass determination. The peak of axion flux is likely to produce gamma-rays in the $\leq$ 1 MeV energy range and so future observations with medium energy gamma-ray missions, such as AMEGO and e-ASTROGAM, will be vital to further constrain UL $m_a$.