Spectro-polarimetric observations of the CIZA J2242.8+5301 northern radio relic: no evidence of high-frequency steepening

TL;DR

This study presents high-frequency radio observations of the CIZA J2242.8+5301 northern relic, finding no spectral steepening up to 18.6 GHz and revealing its polarization properties, which inform particle aging and magnetic field structure.

Contribution

First high-frequency polarimetric observations of this relic showing a consistent power-law spectrum without steepening and detailed magnetic field alignment.

Findings

Spectral index of 1.12±0.03 from 145 MHz to 18.6 GHz

No evidence of spectral steepening at high frequencies

Polarization fraction of about 40% with magnetic fields aligned with relic filaments

Abstract

Observations of radio relics at very high frequency (>10 GHz) can help to understand how particles age and are (re-)accelerated in galaxy cluster outskirts and how magnetic fields are amplified in these environments. In this work, we present new single-dish 18.6 GHz Sardinia Radio Telescope and 14.25 GHz Effelsberg observations of the well known northern radio relic of CIZA J2242.8+5301. We detected the relic which shows a length of $\sim$1.8 Mpc and a flux density equal to $\rm S_{14.25\,GHz}=(9.5\pm3.9)\,mJy$ and $\rm S_{18.6\,GHz}=(7.67\pm0.90)\,mJy$ at 14.25 GHz and 18.6 GHz respectively. The resulting best-fit model of the relic spectrum from 145 MHz to 18.6 GHz is a power-law spectrum with spectral index $\alpha=1.12\pm0.03$: no evidence of steepening has been found in the new data presented in this work. For the first time, polarisation properties have been derived at 18.6 GHz, revealing an averaged polarisation fraction of $\sim40\%$ and a magnetic field aligned with the 'filaments' or 'sheets' of the relic.