The type Iax supernova, SN 2015H

Abstract

We present results based on observations of SN 2015H which belongs to the small group of objects similar to SN 2002cx, otherwise known as type Iax supernovae. The availability of deep pre-explosion imaging allowed us to place tight constraints on the explosion epoch. Our observational campaign began approximately one day post-explosion, and extended over a period of about 150 days post maximum light, making it one of the best observed objects of this class to date. We find a peak magnitude of M r = −17.27 ± 0.07, and a (∆m 15 ) r = 0.69 ± 0.04. Comparing our observations to synthetic spectra generated from simulations of deflagrations of Chandrasekhar mass carbon-oxygen white dwarfs, we find reasonable agreement with models of weak deflagrations that result in the ejection of ∼0.2 M of material containing ∼0.07 M of 56 Ni. The model light curve however, evolves more rapidly than observations, suggesting that a higher ejecta mass is to be favoured. Nevertheless, empirical modelling of the pseudobolometric light curve suggests that 0.6 M of material was ejected, implying that the white dwarf is not completely disrupted, and that a bound remnant is a likely outcome.

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

“…Thus, the N5-3T and N5-2T models demonstrate that the differences between SN 2005hk at −3 d and PS1-12bwh at −2 d cannot be accounted for by simply adjusting for the slight differences in epoch and luminosity. We tested a variety of models with shorter rise times than the 21.8 d observed for SN 2005hk Magee et al 2016). We find that the pre-maximum spectrum of PS1-12bwh cannot be accounted for simply by shortening the rise time to peak.…”

“…We limit this comparison to ±20 d relative to r-band maximum as an indication of the rise and decline of these objects. With the exception of SN 2008ha, all objects have comparable decline rates in the r-band, from 0.60 (PS1-12bwh) to 0.70 (SN 2005hk, Stritzinger et al 2015) and a spread of absolute peak magnitudes, from M r ∼ −17.3 (SN 2015H, Magee et al 2016) to M r ∼ −18.6 (SN 2012Z, Stritzinger et al 2015). These values can be compared with M r ∼ −19.24 for SNe Ia (Hicken et al 2009).…”

“…Most notably, SNe Iax can be fainter than normal SNe Ia (Li et al 2003) by up to five magnitudes (Valenti et al 2009;Foley et al 2009). They also display large variations in their light curve shapes, which show a broader range of decline rates 0.3 ∆m 15 (r) 1.1 (SN 2009ku, SN 2008ha, Narayan et al 2011Stritzinger et al 2014, respectively), and rise times, from ∼10 d (SN 2010ae, Stritzinger et al 2014;Magee et al 2016) to ∼22 d (SN 2005hk, Phillips et al 2007Magee et al 2016), when compared to normal SNe Ia. The fact that many SNe Iax have neither well-constrained peak magnitudes nor decline rates, and even fewer have secure rise time measurements, has further added to the difficulty in interpreting the observed behaviour of SNe Iax.…”

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).…”

“…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). However, SN Iax have significantly slower declines in redder bands, e.g., ∆m 15 (R) 0.2 to 0.8 mag, compared to normal SN Ia which have ∆m 15 (R) 0.6 to 0.8 mag (Magee et al 2016). Faster rising SN Iax are generally faster fading as well, with some exceptions, like SN 2007qd (McClelland et al 2010).…”