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R. Petre (NASA / GSFC), R.L. Shelton (Johns Hopkins University), K.D. Kuntz (GSFC / UMBC)
We present the results of a Chandra ACIS observation of the evolved mixed-morphology SNR W44. We have performed spatially resolved spectroscopy of both the thermal X-ray gas and the embedded Pulsar Wind Nebula (PWN) surrounding pulsar PSR B1853+01.
We compare the properties of the thermal gas against the predictions of models purporting to account for the centrally filled X-ray emission characteristic of mixed morphology remnants. We find a significant radial abundance gradient in Ne, Mg, S, Si, and possibly Fe. The Ne gradient cannot be due to dust destruction, and thus must be due to ejecta enrichment. Spectral fits also indicate that the Fe is both deficient and less ionized than other species, providing the first X-ray evidence for dust destruction in a SNR. The combination of abundance gradient, post adiabatic phase evolution, ejecta enrichment, and dust destruction are all required to explain the surface brightness profile and spectral variations within W44.
The X-ray PWN is clearly distinguished from the thermal emission from W44 at energies above 2 keV. The nebula is asymmetrical, trailing the pulsar to the north. Its extent is approximately half that of the radio nebula, and it shows clear morphological differences. Spectral fitting reveals a clear difference in spectral index between the hard emission from PSR B1853+01 and the extended nebula. The inferred values for X-ray flux and spectral index are used to refine estimates for PWN parameters, including the magnetic field strength, the average Lorentz factor \gamma of the particles in the wind, and the magnetization parameter \sigma.
Bulletin of the American Astronomical Society,
© 2003. The American Astronomical Soceity.