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Probing Non-thermal Cluster Emission with Gamma-Ray and Radio Data

Probing Non-thermal Cluster Emission with Gamma-Ray and Radio Data. Tesla Jeltema University of California, Santa Cruz. Non-Thermal Emission - Sources. Cosmic Rays: accelerated in accretion and merger shocks, AGN, and supernovae - CR protons can survive for a long time

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Probing Non-thermal Cluster Emission with Gamma-Ray and Radio Data

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  1. Probing Non-thermal Cluster Emission with Gamma-Ray and Radio Data Tesla Jeltema University of California, Santa Cruz

  2. Non-Thermal Emission - Sources • Cosmic Rays: accelerated in accretion and merger shocks, AGN, and supernovae • - CR protons can survive for a long time • - CR electrons lose energy quickly • Dark Matter: annihilation or decay of WIMPs to Standard Model particles • Star Formation: emission associated to cosmic rays accelerated by supernovae in cluster galaxies • AGN: (not discussed here)

  3. Non-Thermal Emission - Mechanisms Cosmic Rays Dark Matter Hadronic production or or turbulent reacceleration of lower energy e- (models for positron fraction)

  4. Non-Thermal Emission - Observations • Emission from synchrotron (radio), IC scattering of CMB (X-ray or gamma-ray), and π0 decay (gamma-ray). • Radio: Mpc scale radio emission in • some, but not all clusters •  implies active e- production • over a large area •  limits e- production in non-detections • Gamma-ray: diffuse emission not yet found •  limits CR protons, dark matter, and • total star formation Preliminary Zimmer for Fermi-LAT, TeV PA 2011

  5. Constraints - Cosmic Rays • The Fermi non-detection of clusters implies: • low cosmic ray densities of < 1-10% of the thermal energy density in nearby clusters. •  high B fields in the hadronic model of radio halos. Turbulent acceleration model preferred. Fermi limits to low CR densities and high magnetic fields Jeltema & Profumo 2011

  6. Constraints - Dark Matter • The non-detection of both radio and gamma-ray emission limits the DM annihilation cross-section •  conservative limits exclude thermal cross-section for low DM mass •  excludes much of parameter space fitting e+ excess Example Radio Limits Example Fermi Limits best Fermi cluster limits NFW only Storm, Jeltema, Profumo, & Rudnick 2013 Ackermann et al. 2010

  7. Star Formation - Predictions • Gamma-ray luminosity correlates strongly with star formation rate (total IR or radio luminosity) for galaxies • Gives predicted minimum gamma-ray emission from cluster galaxies. Ackermann et al. 2012  Star formation should account for at least 10% of gamma-ray emission from some clusters. Storm, Jeltema, & Profumo 2012

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