Spectrophotometric Comparison between Type Ia Supernovae 2011by and 2011fe
Abstract
Type Ia supernovae (SNe Ia) that are spectrophotometric "twins" — with spectral features and colors well-matched during the photospheric phase — have been shown to have a per-object RMS scatter of their peak luminosity in the 0.07 - 0.08 mag range (Fakhouri et al. 2015), or ~0.11 mag for a pair of SN twins. The spectral features of SN 2011by are well-matched to SN 2011fe, but that the Cepheid-based relative distance (Foley et al. 2018) implies a luminosity difference between these two SNe Ia of ~0.34 mag. Accounting for the scatter in both Cepheid and twin SN distances, this is a difference of ~2.6 sigma. Using the self-consistent, multi-epoch, spectrophotometric observations of these two SNe spanning 3300 - 9200 A obtained by the Nearby Supernova Factory (SNfactory), we carry out a phase-matched comparison of SN 2011by and SN 2011fe. In agreement with broad-band photometry, we find that these two apparent twin SNe Ia are significantly discrepant at early phases. Using only post-maximum data - the period when the luminosities are most discrepant but where the two SNe otherwise behave similarly, we find evidence for slightly more dust, with slightly higher RV, which reduces the discrepancy to 1.8 sigma. While statistically rare, this combination of SNe Ia highlights the need to be vigilant for discrepancies between SNe Ia proposed as spectrophotometric twins.
- Publication:
-
American Astronomical Society Meeting Abstracts #235
- Pub Date:
- January 2020
- Bibcode:
- 2020AAS...23527603H