Growing evidence that SNe Iax are not a one-parameter family

Abstract

In this study, we present observations of a type Iax supernova, PS1-12bwh, discovered during the Pan-STARRS1 3π-survey. Our analysis was driven by previously unseen pre-maximum, spectroscopic heterogeneity. While the light curve and post-maximum spectra of PS1-12bwh are virtually identical to those of the well-studied type Iax supernova, SN 2005hk, the −2 day spectrum of PS1-12bwh does not resemble SN 2005hk at a comparable epoch; instead, we found it to match a spectrum of SN 2005hk taken over a week earlier (−12 day). We are able to rule out the cause as being incorrect phasing, and argue that it is not consistent with orientation effects predicted by existing explosion simulations. To investigate the potential source of this difference, we performed radiative transfer modelling of both supernovae. We found that the pre-maximum spectrum of PS1-12bwh is well matched by a synthetic spectrum generated from a model with a lower density in the high velocity ( 6000 km s −1 ) ejecta than SN 2005hk. The observed differences between SN 2005hk and PS1-12bwh may therefore be attributed primarily to differences in the high velocity ejecta alone, while comparable densities for the lower velocity ejecta would explain the nearly identical post-maximum spectra. These two supernovae further highlight the diversity within the SNe Iax class, as well as the challenges in spectroscopically identifying and phasing these objects, especially at early epochs.

Extended optical/NIR observations of Type Iax supernova 2014dt: Possible signatures of a bound remnant

“…For example, SN Iax 2014ck showed spectra similar to SN 2008ha, whereas the LCs were similar to SNe 2002cx and 2005hk (Tomasella et al 2016). PS1-12bwh showed a spectral evolution similar to that of SN 2005hk in the post-maximum phase, whereas the pre-maximum evolution showed significant difference (Magee et al 2017). SN 2012Z showed close similarity to SN 2005hk in its early phase spectra.…”

Type Iax supernovae as a few-parameter family

“…The host galaxy reddening was studied via interstellar polarization and Na D lines ) and found to be E(B − V) = 0.09 mag. Different kinds of spectral modeling were carried out by Phillips et al (2007), Sahu et al (2008) and Magee et al (2017); while the authors of the former paper used SYNOW (Fisher 2000), the latter studies employed the Monte Carlo spectrum synthesis codes of Mazzali (2000), and Kerzendorf & Sim (2014), respectively.…”

“…The transition velocity appears at 10 000 km s −1 ; lower, than in the case of the more luminous SNe 2011ay and 2012Z. Magee et al (2017) used TARDIS to compare the Figure 15. Same as Fig.…”

Type Iax Supernovae

“…It is also a primary criterion, as the first two criteria listed above naturally result from spectral similarity. We note that this criterion is no more subjective than the one used to distinguish between light curves showing significant variety (Magee et al 2016(Magee et al , 2017. The B and V -band decline rates are similar to normal SN Ia, though generally also on the faster side (Stritzinger et al 2015), and the optical color evolution in SN Iax (e.g., in B −V ) has a shape roughly similar to normal SN Ia (Foley et al 2013).…”