A Stacked Analysis of GeV Gamma-Ray Emission from SPT-SZ Galaxy Clusters with 16 Years of Fermi-LAT Data
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| Format: | Preprint |
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2025
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| _version_ | 1866913873926291456 |
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| author | Manna, Siddhant Desai, Shantanu |
| author_facet | Manna, Siddhant Desai, Shantanu |
| contents | We report a statistically significant detection of cumulative $γ$-ray emission from a stacked sample of SPT-SZ selected galaxy clusters using 16.4 years of data from the Fermi Gamma-Ray Space Telescope's Large Area Telescope (LAT). By analyzing a population of clusters with individual Test Statistic (TS) values $<$ 9.0, we identify a robust cumulative signal with a TS of 75.2, which corresponds to approximately $8.4σ$ significance. In contrast, clusters with TS $<$ 4.0 yield a weaker cumulative signal of TS equal to 9.65 (2.65$σ$), consistent with background fluctuations. The derived $γ$-ray spectrum is well characterized by a power law model with a best-fit spectral index of $-2.59 \pm 0.20$ and an integrated flux of $1.67^{+1.35}_{-1.07} \times 10^{-11}$ ph cm$^{-2}$ s$^{-1}$. The high TS values in the full sample are likely driven by AGN-dominated clusters. However, when clusters with TS between 4 and 9 are excluded, the remaining low-TS population shows a stacked signal consistent with hadronic emission. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2502_15235 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | A Stacked Analysis of GeV Gamma-Ray Emission from SPT-SZ Galaxy Clusters with 16 Years of Fermi-LAT Data Manna, Siddhant Desai, Shantanu High Energy Astrophysical Phenomena Cosmology and Nongalactic Astrophysics We report a statistically significant detection of cumulative $γ$-ray emission from a stacked sample of SPT-SZ selected galaxy clusters using 16.4 years of data from the Fermi Gamma-Ray Space Telescope's Large Area Telescope (LAT). By analyzing a population of clusters with individual Test Statistic (TS) values $<$ 9.0, we identify a robust cumulative signal with a TS of 75.2, which corresponds to approximately $8.4σ$ significance. In contrast, clusters with TS $<$ 4.0 yield a weaker cumulative signal of TS equal to 9.65 (2.65$σ$), consistent with background fluctuations. The derived $γ$-ray spectrum is well characterized by a power law model with a best-fit spectral index of $-2.59 \pm 0.20$ and an integrated flux of $1.67^{+1.35}_{-1.07} \times 10^{-11}$ ph cm$^{-2}$ s$^{-1}$. The high TS values in the full sample are likely driven by AGN-dominated clusters. However, when clusters with TS between 4 and 9 are excluded, the remaining low-TS population shows a stacked signal consistent with hadronic emission. |
| title | A Stacked Analysis of GeV Gamma-Ray Emission from SPT-SZ Galaxy Clusters with 16 Years of Fermi-LAT Data |
| topic | High Energy Astrophysical Phenomena Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2502.15235 |