AI 中文总结
该研究利用费米大面积望远镜数据搜索PSZ G181.06+48.47星系团的GeV伽马射线发射，通过分箱似然分析和不同模型拟合，发现其伽马射线发射空间扩展，符合弥漫的星系团内发射，给出了相关探测显著性、光子指数和通量等结果。
AI 中文摘要
我们利用17.9年的费米大面积望远镜数据，搜索星系团PSZ2 G181.06+48.47在1 - 300 GeV能量范围内的高能伽马射线。采用16年源目录的分箱似然分析显示，该星系团位置存在显著的伽马射线过剩。将发射建模为点源时，探测显著性为TS = 19.0（4.3σ），光子指数为Γ = 3.20 ± 0.62，积分光子通量为(9.75 ± 2.74)×10⁻¹¹ ph cm⁻² s⁻¹，但星系团中心仍有显著的剩余发射。用径向高斯空间模板取代点源假设显著改善了拟合，最佳宽度为σ = 0.4°，扩展显著性为TS_ext = 36.8（6.0σ）。采用的高斯模型得到源探测显著性为TS = 55.0（7.4σ），光子指数为Γ = 2.62 ± 0.26，积分光子通量为(3.22 ± 0.50)×10⁻¹⁰ ph cm⁻² s⁻¹，同时将星系团位置的剩余发射降低到与零一致的水平。星系团光谱能量分布仅在最低能量区间（1.0 - 3.13 GeV）有显著发射，而所有更高能量区间与上限一致，表明是软伽马射线谱，没有高于约5 GeV发射的证据。这些结果有力证明，与PSZ2 G181.06+48.47相关的伽马射线发射在σ≈0.4°尺度上空间扩展，更符合弥漫的星系团内发射，而非单个未分辨的点源。
英文摘要
We present a search for high energy gamma rays in the energy range from 1--300~GeV from the galaxy cluster PSZ2~G181.06+48.47 using 17.9~years of Fermi-LAT data. A binned likelihood analysis employing the 16-year source catalog reveals a significant $γ$-ray excess at the cluster position. Modelling the emission as a point source yields a detection with $\mathrm{TS}=19.0 (4.3 σ)$, a photon index of $Γ=3.20 \pm 0.62$, and an integrated photon flux of $(9.75\pm2.74)\times10^{-11}\,\mathrm{ph\,cm^{-2}\,s^{-1}}$, but leaves statistically significant residual emission at the cluster center. Replacing the point-source hypothesis with a RadialGaussian spatial template significantly improves the fit, with a preferred width of $σ=0.4^{\circ}$ and an extension significance of $\mathrm{TS}_{\rm ext}=36.8 (6.0σ)$. The adopted Gaussian model yields a source detection significance of $\mathrm{TS}=55.0 (7.4σ)$, a photon index of $Γ=2.62\pm0.26$, and an integrated photon flux of $(3.22\pm0.50)\times10^{-10}\,\mathrm{ph\,cm^{-2}\,s^{-1}}$, while reducing the residual emission at the cluster position to a level consistent with zero. The cluster spectral energy distribution shows significant emission only in the lowest energy interval (1.0--3.13~GeV), while all higher-energy bins are consistent with upper limits, indicating a soft $γ$-ray spectrum with no evidence for emission above $\sim5$~GeV. These results provide strong evidence that the $γ$-ray emission associated with PSZ2~G181.06+48.47 is spatially extended on a scale of $σ\approx0.4^{\circ}$ and is more consistent with diffuse intracluster emission than with a single unresolved point source.
Comments24 pages, 6 figures, 6 tables
