High-resolution international LOFAR observations of 4C 43.15

Radio sources with steep spectra are preferentially associated the most distant galaxies, $\alpha-z$ relation, but reason for this relation is an open question. The spatial distribution of in high-z radio can be used to study and low-frequency observations particularly important understanding particle acceleration injection mechanisms. However, small angular sizes together inherently low resolution telescopes until now has prevented high objects. Here we present subarcsecond a $z = 2.4$ galaxy at frequencies between $121$ MHz $166$ MHz. We measure spectra, discuss implications models relation. targeted 4C 43.15 High Band Antennas (HBAs) \textit{International LOFAR Telescope} (ILT) range baselines up $1300\ \mathrm{km}$. At central frequency $143$ achieve $\sim 0.3''$. By complementing our data archival \textit{Very Large Array} (VLA) spectral index across $55\ \mathrm{MHz}$ $8.4\ \mathrm{GHz}$ resolutions $0.4''$ $0.9''$. With magnetic field strength $B 5.2$ nT fitted indices $\alpha^\mathrm{north}_\mathrm{inj} -0.8$ $\alpha^\mathrm{south}_\mathrm{inj} -0.6$, fitting Tribble ageing model results age $\tau_\mathrm{spec} 1.1 \pm 0.1$ Myr. conclude that on indicates inverse Compton losses could become comparable or exceed synchrotron higher redshifts viable explanation