SN2006bt displays characteristics unlike those of any other known Type Ia supernova (SN Ia). We present optical light curves and spectra of SN2006bt which demonstrate the peculiar nature of this object. SN2006bt has broad, slowly declining light curves indicative of a hot, high-luminosity SN, but lacks a prominent second maximum in the i band as do low-luminosity SNeIa. Its spectra are similar to those of low-luminosity SNeIa, containing features that are only present in cool SN photospheres. Light-curve fitting methods suggest that SN2006bt is reddened by a significant amount of dust; however, it occurred in the outskirts of its early-type host galaxy and has no strong Na D absorption in any of its spectra, suggesting a negligible amount of host-galaxy dust absorption. C II is possibly detected in our pre-maximum spectra, but at a much lower velocity than other elements. The progenitor was likely very old, being a member of the halo population of a galaxy that shows no signs of recent star formation. SNeIa have been very successfully modeled as a one-parameter family, and this is fundamental to their use as cosmological distance indicators. SN2006bt is a challenge to that picture, yet its relatively normal light curves allowed SN2006bt to be included in cosmological analyses. We generate mock SN Ia data sets which indicate that contamination by similar objects will both increase the scatter of a SN Ia Hubble diagram and systematically bias measurements of cosmological parameters. However, spectra and rest-frame i-band light curves should provide a definitive way to identify and eliminate such objects.
- Supernovae: general
- Supernovae: individual (SN 2006bt)
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science