Radio and X-ray connection in radio mini-halos: implications for hadronic models

Abstract

The radio mini halos (MH) observed in relaxed clusters probe the presence of relativistic particles on scales of hundreds of kpc, beyond the scales directly influenced by the central AGN, but the nature of the mechanism that produces the relativistic electrons is still debated. In this work we explore the connection between thermal and non-thermal components of the ICM in a sample of MH and we study its implications for hadronic models for the origin of the relativistic electrons. We studied the thermal and non-thermal connection by carrying out a point-to-point comparison of the radio and the X-ray surface brightness. We extended the method generally applied to giant radio halos by considering the effects of a grid randomly generated through a Monte Carlo chain. Contrary to what is generally observed for giant radio halos, we find that the mini-halos in our sample have super-linear scaling between radio and X-rays, which suggests a peaked distribution of relativistic electrons and magnetic field. We used the radio and X-ray correlation to constrain the physical parameters of a hadronic model and we compared the model predictions with current observations. Specifically, we focus on a model where cosmic rays are injected by the central AGN and they generate secondaries in the ICM, and we assume that the role of turbulent re-acceleration is negligible. This model allows us to constrain the AGN cosmic ray luminosity in the range $\sim 10^{44-46}$ erg s${}^{-1}$ and the central magnetic field in the range 10-40 $\mu$G. The resulting $\gamma$-ray fluxes calculated assuming these model parameters do not violate the upper limits on $\gamma$-ray diffuse emission set by the Fermi-LAT telescope. Further studies are now required to explore the consistency of these large magnetic fields with Faraday rotation studies and to study the interplay between the secondary electrons and the ICM turbulence.

17 pages, 13 figures. Accepted for publication on A&A

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• The galaxy group NGC 507: newly detected AGN remnant plasma transported by sloshing
• On the relation between mini-halos and AGN feedback in clusters of galaxies
• Radio fossils, relics, and haloes in Abell 3266: cluster archaeology with ASKAP-EMU and the ATCA
• A MeerKAT-meets-LOFAR Study of MS 1455.0+2232: A 590 kiloparsec 'Mini'-Halo in a Sloshing Cool-Core Cluster
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• A MeerKAT-meets-LOFAR study of Abell 1413: a moderately disturbed non-cool-core cluster hosting a $\sim 500$ kpc 'mini'-halo
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• Chandra and XMM-Newton observations of A2256: cold fronts, merger shocks, and constraint on the IC emission
• Radio halos and relics from extended cosmic-ray ion distributions with strong diffusion in galaxy clusters
• uGMRT detection of cluster radio emission in low-mass Planck~SZ clusters
• Prospects for $\gamma$-ray observations of the Perseus galaxy cluster with the Cherenkov Telescope Array
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• Extended radio emission in the galaxy cluster MS 0735.6+7421 detected with the Karl G. Jansky Very Large Array
• The Merger Dynamics of the X-ray Emitting Plasma in Clusters of Galaxies
• Constraining the magnetic field in the galaxy cluster Abell 2142 using MeerKAT L-band polarisation data
• The Coma cluster at LOFAR frequencies II: the halo, relic, and a new accretion relic
• A deep study of A399-401: An application for wide-field facet calibration
• uGMRT and MeerKAT observation of RXCJ0232-4420: a quiet cluster with a giant radio halo
• Discovery of large-scale radio emission enveloping the mini-halo in the most X-ray luminous galaxy cluster RX~J1347.5-1145
• Cosmological simulation of a radio synchrotron bridge between pre-merging galaxy clusters