G328.4+0.2: A Large and Luminous Crab-like Supernova Remnant

We report on radio continuum and H I observations of the radio source G328.4+0.2 using the Australia Telescope Compact Array. Our results confirm G328.4+0.2 to be a filled-center nebula with no surrounding shell, showing significant linear polarization and an almost flat spectral index. These results lead us to conclude that G328.4+0.2 is a Crab-like, or "plerionic," supernova remnant (SNR), presumably powered by an unseen central pulsar. H I absorption toward G328.4+0.2 puts a lower limit on its distance of 17.4 ± 0.9 kpc, making it the largest (D = 25 pc) and most luminous (L_R = 3 × 10³⁵ ergs s^-1) Crab-like SNR in the Galaxy. We infer G328.4+0.2 to be significantly older than the Crab Nebula, but powered by a pulsar which is fast spinning (P < 20 ms) and which has a comparatively low magnetic field (B < 10¹² G). We propose G328.4+0.2, G74.9+1.2, and N157B as a distinct group of large-diameter, high-luminosity Crab-like SNRs, all powered by fast-spinning low-field pulsars.