Ping

Whether the progenitors of Type Ia Supernovae, 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 12CO J=2–1 mapping and a 3-mm line survey towards the remnant using the IRAM 30 m telescope. We show that Tycho is surrounded by a highly clumpy molecular bubble at the local standard of rest velocity VLSR ∼62kms−1 which has an expanding velocity of ∼ 5 km s−1 and a mass of ∼ 220 M⊙ (at the distance of 2.5 kpc). Enhanced 12CO J=2–1 line emission relative to 12CO J=1–0 emission and possible line broadenings (in velocity range −64–−60 kms−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 molecular bubble at the velocity range from −66 kms−1 to −57 kms−1. The most plausible origin for the expanding bubble is the fast outflow (with velocity > 100 km s−1) driven from the vicinity of a massive WD as it accreted matter from a non-degenerate 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 expanding bubble presents new evidence for the progenitor of Tycho being a single-degenerate system.