NGC 315 VLBA maps

We observe remarkably steep values for the spectral index on sub-parsec scales (similar to -2) which flatten around -0.8 on parsec scales. We suggest that the observed steep values may result from particles being accelerated via diffusive shock acceleration mechanisms in magnetized plasma and subsequently experiencing cooling through synchrotron losses. The brightness temperature of the 43GHz cores indicates a dominance of the magnetic energy at the jet base, while the cores at progressively lower frequencies reveal a gradual transition towards equipartition.

Based on the spectral index and brightness temperature along the incoming jet, and by employing theoretical models, we derive that the magnetic field strength has a close-to-linear dependence with distance going from parsec scales up to the jet apex.