We have mapped the powerful radio galaxy Hercules A at six frequencies spanning 1295 to 8440 MHz using the VLA in all four configurations .
Here we discuss the structure revealed in total intensity , spectral index , polarization , and projected magnetic field .

Our observations clearly reveal the relation between the bright jets , prominent rings , bulbous outer lobes and faint bridge that make up the radio source .
The jets and rings form a coherent structure with a dramatically flatter spectrum than the surrounding lobes and bridge , strongly suggesting that they represent a recently renewed outburst from the active nucleus .
The spectrum of the lobes is also steeper than in typical radio sources , and steepens further towards the centre .
The compact core is optically thin and also has a remarkably steep spectrum ( \alpha \simeq - 1.2 ) .
There is some evidence that the old lobe material has been swept up and compressed ahead of the new outburst .
We interpret the dramatic asymmetry in the bright structure , and more subtle differences between diffuse lobe structures , in terms of relativistic beaming combined with front-to-back light-travel delays which mean that we view the two lobes at different stages of the outburst .

After correcting for Faraday rotation the projected magnetic field closely follows the edge of the lobes , the jets , and the rings ; the field pattern in the two lobes is broadly similar .
We confirm a strong asymmetry in depolarization and Faraday rotation , with the jet side the less depolarized and the flatter spectrum , consistent with general correlations between these asymmetries .
The spectral index asymmetry is clearly present in the ‘ old ’ lobe material and so , at least in this case , is not due to beaming ; but it can be understood in terms of the light-travel delay .