We present new observational results obtained for the Galactic non-thermal radio source G328.4+0.2 to determine both if this source is a pulsar wind nebula or supernova remnant , and in either case , the physical properties of this source .
Using X-ray data obtained by XMM , we confirm that the X-ray emission from this source is heavily absorbed and has a spectrum best fit by a power law model of photon index \Gamma = 2 with no evidence for a thermal component , the X-ray emission from G328.4+0.2 comes from a region significantly smaller than the radio emission , and that the X-ray and radio emission are significantly offset from each other .
We also present the results of a new high resolution ( 7 ^ { \prime \prime } ) 1.4 GHz image of G328.4+0.2 obtained using the Australia Telescope Compact Array , 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 ( \alpha \approx 0 ; S _ { \nu } \propto \nu ^ { \alpha } ) , though some areas of the eastern edge of G328.4+0.2 have a steeper radio spectral index of \alpha \sim - 0.3 .
Additionally , we searched without success for a central radio pulsar , and obtain a luminosity limit of L _ { 1400 } < \lesssim 30 mJy kpc ^ { 2 } , assuming a distance of 17 kpc .
In light of these observational results , we test if G328.4+0.2 is a pulsar wind nebula ( PWN ) or a large PWN inside a supernova remnant ( SNR ) using a simple hydrodynamic model for the evolution of a PWN inside a SNR .
As a result of this analysis , we conclude that G328.4+0.2 is a young ( \lesssim 10000 years old ) pulsar wind nebula formed by a low magnetic field ( \lesssim 10 ^ { 12 } G ) neutron star born spinning rapidly ( \lesssim 10 ms ) expanding into an undetected SNR formed by an energetic ( \gtrsim 10 ^ { 51 } ergs ) , low ejecta mass ( M _ { ej } \lesssim 5 M _ { \odot } ) supernova explosion which occurred in a low density ( n \sim 0.03 cm ^ { -3 } ) environment .
If correct , the low magnetic field and fast initial spin period of this neutron star poses problems for models of magnetar formation which require fast initial periods .