Other
Scientific paper
Aug 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004head....8.2409r&link_type=abstract
American Astronomical Society, HEAD meeting #8, #24.09; Bulletin of the American Astronomical Society, Vol. 36, p.950
Other
Scientific paper
We present a high angular resolution Chandra observation and narrow-band optical images of the archetypical mixed-morphology supernova remnant (SNR) W28. The Chandra observation covered the central and southwestern regions of W28: we have augmented this dataset with a mosaicked ROSAT HRI image that samples the entire angular extent of this SNR. Previous ASCA and ROSAT studies of W28 have shown that the plasma conditions differ from other mixed-morphology SNRs in that X-ray spectral variations are seen across W28. The Chandra image reveals that the X-ray emission from the center of this SNR is very clumpy: this central emission is several arcminutes in size and irregular in shape. The spectrum of this central X-ray emission is reasonably fit by an ionization equilibrium thermal model, but two components to this model are required for an adequate fit. Among mixed-morphology SNRs, the presence of a high temperature component is still unique to W28. Also, compared to the hard X-ray emission, the soft X-ray emission from the center of W28 is associated with smaller scale structures. In addition, we find that along the northern boundary of the SNR, the X-ray emission is very soft: this result indicates that the X-ray emitting plasma has significantly cooled at the site of interaction with adjacent clouds. Our mosaicked ROSAT HRI image reveals a surprisingly clumpy structure along the northwestern rim of W28 which resembles a broken shell rather than a smooth shell: such clumpy structure has never been seen before in the shells of SNRs. Finally, our Chandra observation has resolved a hard X-ray source located 20 arcminutes southwest of the center of W28 and on the shell of the SNR: the spectrum of this source is well-fit with a power-law model, suggesting non-thermal emission, which is either pulsar nebula or a background AGN. We will compare the high resolution X-ray image of W28 with our optical images and discuss several mechanisms that may explain the center-filled X-ray emission of this SNR.
Borkowski Kazik
Keohane Jonathan W.
Pannuti Thomas G.
Rho Jeonghee
Winkler Frank P.
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