Supernova Remnants in the Magellanic Clouds. II. Supernova Remnant Breakouts from N11L and N86

Abstract

The evolution of a supernova remnant (SNR) is heavily influenced by the interstellar conditions surrounding the remnant. This is particularly true in cases where the SNR is breaking out into a low-density area in the surrounding medium. We examine two promising candidates for the study of SNR breakouts in the Large Magellanic Cloud (LMC): N11L and N86. The remnant N11L has a filamentary extension that interrupts the shell; to the north of this extension, we find a region of diffuse radio and X-ray emission that shows only faint filaments in optical images. The discontinuous distribution of velocities in the shell material and the apparent flattening of the radio spectral index in the outflow region suggest substantial turbulence in the outflowing material and clumpiness in the surrounding interstellar medium (ISM). N86, on the other hand, shows a large breakout to the north, as well as several smaller possible outflows around the shell. We find that the northern breakout has a well-defined spherical expansion pattern, faint diffuse X-ray emission, and a highly filamentary optical structure. Our velocity data indicate that material breaking out to the north is expanding at a maximum of 100 km s−1. The consequences of these breakouts on the parent remnants are discussed: N11L appears to have a lower thermal energy, by an order of magnitude, than other LMC remnants used for comparison. N86, on the other hand, shows a thermal energy fairly similar to the comparison SNRs, perhaps due to a more gradual loss of hot gas. The implications of the breakout structures for the surrounding medium are also discussed. The breakout in N11L coincides with a possible low-density cavity, which is enclosed in a shell structure on the western edge of the N11 H II complex. The less dense shell of N86 and the more distributed pattern of the breakouts suggest a relatively low density ISM with substantial local density variations.