Multi-Wavelength Signatures of a Giant Cometary Radio Halo in MACSJ0417-1154

Galaxy clusters hosting diffuse non-thermal radio emission offer direct insight into plasma processes of the intracluster medium (ICM). We present the first multi-frequency study of the radio halo in MACSJ0417 (z = 0.445) using uGMRT (300-850 MHz), MeerKAT (900-1670 MHz), and archival XMM-Newton data. The halo extends to about 1.75 Mpc at 400 MHz, while two candidate relics (R1 and R2) are detected at 2.9 Mpc. The integrated spectra follow single power-laws with spectral indices alpha-1.3 for the halo and alpha-1.6 for the relics. Sensitive uGMRT imaging reveals a radio surface brightness edge about 43 '' SE of the cluster centre, which coincides with an X-ray discontinuity. Resolved spectral maps (400--1280 MHz) show significant fluctuations and a clear radial steepening of the spectral index. X-ray analysis reveals an elongated SE-NW morphology and high-temperature regions (about 11 keV) along this axis. A strong radio and X-ray surface brightness correlation is found (correlation coefficient about 0.85), with the correlation slope evolving from sublinear at 400 MHz to linear at 1280 MHz. These results, together with the spectral properties, support the turbulent re-acceleration model and point to inhomogeneous ICM conditions. The pure hadronic model is excluded owing to unrealistic energy requirements for cosmic-ray protons. We propose that MACSJ0417 is undergoing a minor off-axis dissociative merger (mass ratio about 6:1) along the SE-NW axis, which has preserved its cool core while driving turbulence that powers the giant radio halo.