AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 85. Supernova Remnants and Planetary Nebulae
Display, Thursday, June 3, 1999, 9:20am-4:00pm, Southwest Exhibit Hall

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[85.08] Supernova Remnants in Low-Density Media

S. Kim, Y.-H. Chu, J.R. Dickel (UIUC), R.C. Smith (CTIO)

Supernova remnants (SNRs) are conventionally identified by their bright X-ray emission, nonthermal radio emission, and high [S II]/H\alpha ratio. However, if a supernova has exploded in a low-density medium, its remnant may not exhibit all of these signatures.

Using ROSAT X-ray observations, we have found three SNR candidates in the Large Magellanic Cloud. Two of these candidates, ROSAT sources RX\,J0529.8-6653 and RX\,J0532.4-6732, have radio counterparts and the radio spectra are nonthermal; however, they do not have optical counterparts. The third candidate, RX\,J0573.6-6847, has neither a radio nor an optical counterpart.

We have analyzed the ROSAT PSPC observations of RX\,J0532.4-6732 and RX\,J0573.6-6847 to determine the temperature and density of the X-ray emitting gas. In both cases, the X-ray emitting gas has a temperature (~3\times106 K) similar to what is seen in confirmed SNRs, but the density (0.05--0.1 cm-3) is 1--2 orders of magnitudes lower. The cooling timescale for hot gas at such low densities would be 106--107 yrs. Therefore, it can be assumed that these SNR candidates are in the adiabatic expansion stage, and Sedov's solution can be used to calculate the supernova explosion energy, age of the remnant, and density of the ambient medium. Comparison between these results and those of confirmed SNRs again show that while the energies and ages are similar, the calculated ambient densities are much lower.

Therefore, these SNR candidates must be bona fide remnants. They are the result of supernova explosions in low-density media.

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