High significance detection at 4.8 GHz of the radio halo in the Coma galaxy cluster with the Sardinia Radio Telescope

TL;DR

This study reports the first detection of the Coma galaxy cluster's radio halo at 4.8 GHz using the Sardinia Radio Telescope, revealing a higher flux density and a spectral index suggesting complex electron acceleration mechanisms.

Contribution

First detection of the Coma cluster's radio halo at 4.8 GHz with detailed flux and spectral analysis, highlighting implications for electron acceleration models.

Findings

Radio halo detected at 4.8 GHz with >3σ significance.

Estimated flux density of 61±11 mJy at 4.8 GHz.

Spectral index between 4.8 and 6.6 GHz is ~1.17, indicating spectral steepening.

Abstract

We present the results of observations of the radio halo in the Coma galaxy cluster at 4.8 GHz performed with the Sardinia Radio Telescope. The radio halo in this cluster is detected for the first time at this frequency with a statistical significance higher than $3\sigma$. After the removal of the Radio Frequency Interference and of the discrete sources contribution, and after the correction for the Sunyaev-Zel'dovich effect, we estimate a flux density of $61\pm11$ mJy, higher than the value previously reported in literature at this frequency. By using the value we obtained, it is possible to estimate an integrated spectral index between 4.8 and 6.6 GHz of $\alpha\sim1.17$, where $F(\nu)\propto \nu^{-\alpha}$, indicating a possible higher-frequency slowdown of the spectral steepening observed between 1.4 and 4.8 GHz. Such a spectral behavior is compatible with turbulent re-acceleration if the seed electrons have a spectrum extending up to high energies, as in the case of continuous injection by hadronic interactions or dark matter annihilation. We also report the detection at 4.8 GHz of a polarized spot inside the halo, without an evident counterpart, already detected at 6.6 GHz.