Tyrone

Despite the critical role that SNe Ia play in the chemical enrichment of the Universe and their great importance in measuring cosmological distances, we still don’t know for certain how they arise. In the canonical form of the “single-degenerate” scenario, a white dwarf grows through the nuclear burning of matter accreted at its surface from some companion star. This renders it a hot, luminous object (a supersoft X-ray source or SSS, $10^{5}$ — $10^{6}$K, $10^{38}$erg/s) for up to a million years prior to explosion. Past efforts to directly detect the progenitors of very recent, nearby SNe Ia in archival soft X-ray images have produced only upper limits, and are only constraining assuming progenitors with much higher temperatures than known SSSs. In this talk, I will outline an alternative approach: given that such objects should be strong sources of ionizing radiation, one may instead search the environment surrounding nearby SN Ia remnants for interstellar matter ionized by the progenitor. Such “fossil nebulae” should extend out to tens of parsecs and linger for roughly the recombination timescale in the ISM, of order 10,000 — 100,000 years. Progress on this front has been hampered by the failure to detect nebulae surrounding most known SSSs using 1m class telescopes in the early 1990s. I will present new benchmark calculations for the emission-line nebulae expected to surround such objects, demonstrating that previous non-detections are entirely consistent with the low ISM densities expected in the vicinity of most SN Ia progenitors (Woods & Gilfanov, 2016). Modern large optical telescopes are now well able to reach the required limiting surface brightness needed to find such faint emission. With this in mind, I will introduce our new narrow-band survey for fossil nebulae surrounding young Magellanic SN Ia remnants and SSSs, already underway using the Magellan Baade telescope (PI: Alejandro Clocchiatti). In addition to opening a new era of “SN Ia archaeology,” I will show how our deep observations can also serve as a new probe of the structure of the ISM in nearby galaxies.