On the nature of Type IIn/Ia-CSM supernovae: optical and near-infrared spectra of SN 2012ca and SN 2013dn
Abstract
A growing subset of Type Ia supernovae (SNe Ia) shows evidence via narrow emission lines for unexpected interaction with a dense circumstellar medium (SNe IIn/Ia-CSM). The precise nature of the progenitor, however, remains debated owing to spectral ambiguities arising from a strong contribution from the CSM interaction. Late-time spectra offer potential insight if the post-shock cold, dense shell becomes sufficiently thin and/or the ejecta begin to cross the reverse shock. To date, only a few high-quality spectra of this kind exist. Here we report on the late-time optical and infrared spectra of the SNe Ia-CSM 2012ca and 2013dn. These SNe Ia-CSM spectra exhibit low [Fe III]/[Fe II] ratios and strong [Ca II] at late epochs. Such characteristics are reminiscent of the super-Chandrasekhar-mass candidate SN 2009dc, for which these features suggested a low-ionization state due to high densities, although the broad Fe features admittedly show similarities to the blue `quasi-continuum' observed in some core collapse SNe Ibn and IIn. Neither SN 2012ca nor any of the other SNe Ia-CSM in this paper show evidence for broad oxygen, carbon, or magnesium in their spectra. Similar to the interacting Type IIn SN 2005ip, a number of high-ionization lines are identified in SN 2012ca, including [S III], [Ar III], [Ar X], [Fe VIII], [Fe X], and possibly [Fe XI]. The total bolometric energy output does not exceed 1051 erg, but does require a large kinetic-to-radiative conversion efficiency. All of these observations taken together suggest that SNe Ia-CSM are more consistent with a thermonuclear explosion than a core collapse event, although detailed radiative transfer models are certainly necessary to confirm these results.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- February 2015
- DOI:
- 10.1093/mnras/stu2435
- arXiv:
- arXiv:1408.6239
- Bibcode:
- 2015MNRAS.447..772F
- Keywords:
-
- circumstellar matter;
- supernovae: general;
- supernovae: individual: SN 2005ip;
- supernovae: individual: SN 2009dc;
- supernovae: individual: SN 2012ca;
- supernovae: individual: SN 2013dn;
- Astrophysics - Solar and Stellar Astrophysics;
- Astrophysics - Cosmology and Nongalactic Astrophysics;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 15 pages, 12 figures, 6 tables