Constraining relativistic protons and magnetic fields in galaxy clusters through radio and gamma-ray observations : the case of A2256

Abstract

Giant radio halos are the most relevant examples of diffuse synchrotron emission from galaxy clusters. A number of these sources have very steep spectrum, with spectral index $\alpha \ge 1.5-1.6$ ($F(\nu )\propto {\nu }^{-\alpha }$), and are ideal targets to test current models for the origin of the relativistic particles. A2256 hosts the nearest radio halo with very steep spectrum, with $\alpha =1.61$, and a very large population of relativistic protons in the cluster would be necessary to explain the halo as due to synchrotron emission from secondary particles. In this case the 0.1-1 GeV $\gamma$--ray luminosity is expected 10-20 times larger than that of clusters hosting radio halos with similar radio power at GHz frequencies but with spectra more typical of the presently observed halo population, $\alpha \sim 1.2$. Under these assumptions incoming FERMI/GLAST observations are expected to detect A2256, provided that the magnetic field in the central cluster region is $\le$10-15 $\mu$G. We show that this will allow for a prompt test of hadronic models for the origin of radio halos, and for complementary constraints on both the cluster magnetic field and the physics of particle acceleration mechanisms.

4 pages, 3 figures, to appear in Astronomy and Astrophysics

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Cited by in corpus (11)

• Cosmic rays in galaxy clusters and their non-thermal emission
• Cosmic ray transport in galaxy clusters: implications for radio halos, gamma-ray signatures, and cool core heating
• Acceleration of primary and secondary particles in galaxy clusters by compressible MHD turbulence: from radio halos to gamma rays
• Probing the origin of giant radio halos through radio and gamma-ray data : the case of the Coma cluster
• Implications of Fermi Observations for Hadronic Models of Radio Halos in Clusters of Galaxies
• The very steep spectrum radio halo in Abell 697
• Thermal and non-thermal traces of AGN feedback: results from cosmological AMR simulations
• The LOFAR and JVLA view of the distant steep spectrum radio halo in MACS J1149.5+2223
• Simulations of cosmic rays in large-scale structures: numerical and physical effects
• Diffuse radio emission in the complex merging galaxy cluster Abell 2069
• Probing particle acceleration in Abell 2256: from to 16 MHz to gamma rays