Oral Presentation

Search for High Energy (MeV to GeV) gamma ray emissions from Galaxy Clusters. Results from Fermi-LAT (with stacking), COMPTEL, DAMPE and indirect searches for dark matter.

Author(s): Siddhant Manna & Shantanu Desai

Presenter: Siddhant Manna (Indian Institute of Technology Hyderabad, Telangana, India.)

Galaxy clusters offer a unique laboratory to probe high-energy processes and dark matter (DM) through gamma-ray emission. Using 15–16 years of Fermi-LAT data (1–300 GeV), we systematically searched 300 SPT-SZ clusters, detecting a 6.1σ signal from SPT-CL J2012-5649 (flux ~1.3×10⁻⁶ MeV cm⁻² s⁻¹, spectral index -3.61±0.33), though radio galaxies may contribute. Six other clusters show 3–5σ hints, while stacking clusters with TS<9 yields a robust 8.4σ cumulative signal (index -2.59±0.20), consistent with hadronic cosmic-ray interactions or AGN contributions. In contrast, a DAMPE search (3 GeV–1 TeV) on SPT-CL J2012-5649 found no >3σ signal, setting flux limits (~10⁻⁶–10⁻⁴ MeV cm⁻² s⁻¹) compatible with Fermi-LAT results. At MeV energies (0.75–30 MeV), COMPTEL data from five clusters (e.g., Coma, VIRGO) yielded no detections (flux limits ~10⁻¹⁰ erg cm⁻² s⁻¹), except a marginal 2.5σ VIRGO signal (~10⁻⁹ erg cm⁻² s⁻¹). Searching for DM annihilation (1–300 GeV) in 350 SPT-SZ clusters, we found a 3σ signal from SPT-CL J2021-5257 (mχ=60±11.8 GeV, ⟨σv⟩=6±0.6×10⁻²⁵ cm³ s⁻¹, bb̄ channel), though inconsistent with dwarf galaxy limits, alongside a stringent limit from SPT-CL J0455-4159 (⟨σv⟩=6.44×10⁻²⁶ cm³ s⁻¹, mχ=10 GeV). These results highlight a new era of cluster studies, bridging cosmic rays, AGN, and DM constraints across MeV to GeV energies.