Turbulent magnetic fields in the merging galaxy cluster MACS J0717.5+3745

We present wideband (1 − 6.5 GHz) polarimetric observations, obtained with the Karl G. Jansky Very Large Array, of merging galaxy cluster MACS J0717.5+3745, which hosts one most complex known radio relic and halo systems. used both rotation measure synthesis QU -fitting to find a reasonable agreement results these methods, particularly when Faraday distribution is simple depolarization mild. The highly polarized over its entire length (850 kpc), reaching fractional polarization > 30% in some regions. also observe strong wavelength-dependent for regions relic. northern part shows distribution, suggesting that this region located or behind intracluster medium (ICM). Conversely, southern very close Galactic foreground, rather low dispersion, indicating little magnetoionic material intervening along line sight. Based on spatially resolved analysis, we scatter depths correlated depolarization, tangled magnetic field ICM causes depolarization. conclude could be turbulent. At position well narrow-angle-tailed (NAT), evidence two components are clearly separated space. high dispersion component seems associated NAT, NAT embedded while lies front it. If true, implies not necessarily physically connected and, thus, may, fact, powered by shock re-acceleration fossil electrons from NAT. orientation follows structure well-ordered field. detected emission region; however, absence significant value suggests was previously considered as does, originate shock(s).