Chuan-Jui

N103B is a Type Ia supernova remnant (SNR) projected in the outskirt of
the superbubble around the rich cluster NGC 1850 in the Large Magellanic
Cloud (LMC). We have obtained emph{Hubble Space Telescope(HST)} images to study
the physical structure of this SNR and its underlying stellar population.
We have also obtained high- and medium-dispersion spectra of the SNR to
identify the shocked gas components and to determine the excitation and
abundances of the gas.

The emph{HST} H$alpha$ image of N103B shows an incomplete filamentary
elliptical shell and several groups of prominent knots. Our long-slit,
high-dispersion spectra show that the filamentary shell is dominated by
hydrogen Balmer lines; its lack of forbidden line emission indicates that
the filamentary shell results from collisionless shocks into a mostly
neutral medium. In contrast, the prominent knots show large velocity
widths in both H$alpha$ line and [N II] $lambdalambda$6548, 6583 lines.
Furthermore, the [S II] $lambda$6716/$lambda$6731 ratios in the knots
imply electron densities $>$5000 cm$^{-3}$. These spectral properties
suggest that these knots are most likely circumstellar material ejected by
the progenitor before the SN explosion.

Interestingly, using our high-dispersion spectra, we found that the
N103B SNR is inside a slow expanding shell ($V_{rm exp}~sim$ 10
km~s$^{-1}$). This kinematically identified shell is not visible
morphologically.

Considering the optical and X-ray properties of N103B and the discovery
of the slow expanding shell encompassing the SNR, we suggest that
the progenitor of N103B is a single-degenerate binary system; furthermore,
the progenitor moved through the interstellar medium roughly along the minor
axis of the filamentary elliptical shell. The supernova explosion center
can be approximated by the center of the elliptical shell, and used to
search for the surviving companion of the supernova. We suggest possible
candidates for the surviving companion and implications on its mass and
evolutionary stage.