The radio emission, X-ray emission, and hydrodynamics of G328.4+0.2: A comprehensive analysis of a luminous pulsar wind nebula, its neutron star, and the progenitor supernova explosion

We present new observational and modeling results obtained for the Galactic nonthermal radio source G328.4+0.2. Using X-ray data obtained by XMM-Newton, we confirm that its X-ray emission is heavily absorbed, has a spectrum best fitted by a power-law model of photon index Γ = 2 with no evidence for a thermal component, comes from a region significantly smaller than the radio emission, and that the X-ray and radio emissions are significantly offset from each other. We also present the results of a new high-resolution (7″) 1.4 GHz image of G328.4+0.2 obtained using ATCA and a deep search for radio pulsations using the Parkes radio telescope. By comparing this 1.4 GHz image with a similar resolution image at 4.8 GHz, we find that the radio emission has a flat spectrum (α ≈ 0; S_v ∝ v^α). Additionally, we are able to limit the pseudoluminosity of any pulsar to L₁₄₀₀ ≡ S₁₄₀₀d² ≲ 30 mJy kpc² for the central radio pulsar, assuming a distance of 17 kpc. In light of these observational results, we test whether G328.4+0.2 is a pulsar wind nebula or an SNR that contains a large pulsar wind nebula using a simple hydrodynamic model for the evolution of a pulsar wind nebula inside an SNR. As a result of this analysis, we conclude that G328.4+0.2 is a young (≲10,000 years old) pulsar wind nebula formed by a low magnetic field (≲10¹²G) neutron star born spinning rapidly (≲10 ms) expanding into an undetected SNR formed by an energetic (≳10⁵¹ ergs), low ejecta mass (M_ej ≲ 5 M_⊙) supernova explosion that occurred in a low-density (n ∼ 0.03 cm^-3) environment.