Thirty Years of Radio Observations of Type Ia SN 1972E and SN 1895B: Constraints on Circumstellar Shells

摘要

We have imaged 35 yr of archival Very Large Array observations of the nearby (d _(L)?=?3.15 Mpc) Type Ia supernovae SN 1972E and SN 1895B between 9 and 121 yr post-explosion. No radio emission is detected, constraining their radio luminosities to be L _(ν ,8.5GHz) < 6.0?×?10~(23) erg s~(?1) Hz~(?1) 45 yr post-explosion and L _(ν ,8.5GHz) < 8.9?×?10~(23) erg s~(?1) Hz~(?1) 121 yr post-explosion, respectively. These limits imply a clean circumstellar medium (CSM), with n < 0.9 cm~(?3) out to radii of a few?×10~(18) cm, if the SN blast wave is expanding into uniform density material. We also constrain the presence of CSM shells surrounding the progenitor of SN 1972E. We rule out essentially all medium and thick shells with masses of 0.05–0.3 M _(⊙) at radii between ～10~(17) and 10~(18) cm, and thin shells at specific radii with masses down to ?0.01 M _(⊙). These constraints rule out swaths of parameter space single and double degenerate progenitor scenarios, including recurrent nova, core-degenerate objects, ultra-prompt explosions, and white dwarf (WD) mergers with delays of a few hundred years between the onset of merger and explosion. Allowed progenitors include WD–WD systems with a significant (>10~(4) yr) delay from the last episode of common envelope evolution and single degenerate systems undergoing recurrent nova—provided that the system has been in the nova phase for ?10~(4) yr, such that a large (>10~(18) cm) cavity has been evacuated. Future multi-epoch observations of additional intermediate-aged SNe Ia will provide a comprehensive view of the large-scale CSM around these explosions.