Expanding molecular bubble surrounding Tycho's supernova remnant (SN 1572) observed with IRAM 30 m telescope: evidence for a single-degenerate progenitor

TL;DR

This study presents evidence of a molecular bubble around Tycho's supernova remnant, supporting the single-degenerate progenitor scenario for Type Ia supernovae through IRAM 30 m telescope observations.

Contribution

It provides the first clear detection of an expanding bubble driven by a supernova progenitor, favoring the single-degenerate model for SN 1572.

Findings

Detection of a clumpy molecular bubble expanding at ~4.5 km/s.

Enhanced CO emission and line broadening at the SNR boundary.

Evidence linking the bubble to a WD outflow from a nondegenerate companion.

Abstract

Whether the progenitors of SNe Ia are single-degenerate or double-degenerate white dwarf (WD) systems is a highly debated topic. To address the origin of the Type Ia Tycho's supernova remnant (SNR), SN 1572, we have carried out a $^{12}$CO J=2-1 mapping and a 3-mm line survey toward the remnant using the IRAM 30 m telescope. We show that Tycho is surrounded by a clumpy molecular bubble at a local standard of rest velocity of $\sim 61$ km s$^{-1}$ which expands at a speed of $\sim 4.5$ km s$^{-1}$ and has a mass of $\sim 220$ M$_\odot$ (at the distance of 2.5 kpc). Enhanced $^{12}$CO J=2-1 line emission relative to $^{12}$CO J=1-0 emission and possible line broadenings (in velocity range $-64$ to $-60$ km s$^{-1}$) are found at the northeastern boundary of the SNR, where the shell is deformed and decelerated. These features, combined with the morphological correspondence between the expanding molecular bubble and Tycho, suggest that the SNR is associated with the bubble at the velocity range $-66$ to $-57$ km s$^{-1}$. The most plausible origin for the expanding bubble is the fast outflow (with velocity of hundreds km s$^{-1}$) driven from the vicinity of a WD as it accreted matter from a nondegenerate companion star. The SNR has been expanding in the low-density wind-blown bubble, and the shock wave has just reached the molecular cavity wall. The SNR has been expanding in the low-density wind-blown bubble, and the shock wave has just reached the molecular cavity wall. This is the first unambiguous detection of an expanding bubble driven by the progenitor of a Type-Ia SNR, which constitutes evidence for a single-degenerate progenitor for this SN Ia.