The Nickel Mass Distribution of Normal Type II Supernovae

TL;DR

This study analyzes the distribution of nickel masses in normal Type II supernovae using observational data and compares it with theoretical models, revealing a skewed distribution and compatibility with certain hydrodynamical simulations.

Contribution

It provides the first detailed statistical characterization of nickel mass distribution in Type II supernovae and tests its consistency with existing explosion models.

Findings

Nickel mass distribution is skewed between 0.005 and 0.280 solar masses.

Observed distribution has a median of 0.031 solar masses.

Theoretical models KEPLER and Prometheus Hot Bubble match observations.

Abstract

Core-collapse supernova explosions expose the structure and environment of massive stars at the moment of their death. We use the global fitting technique of Pejcha & Prieto (2015a,b) to estimate a set of physical parameters of 19 normal Type II SNe, such as their distance moduli, reddenings, $^{56}$Ni masses $M_{\rm Ni}$, and explosion energies $E_{\rm exp}$ from multicolor light curves and photospheric velocity curves. We confirm and characterize known correlations between $M_{\rm Ni}$ and bolometric luminosity at 50 days after the explosion, and between $M_{\rm Ni}$ and $E_{\rm exp}$. We pay special attention to the observed distribution of $M_{\rm Ni}$ coming from a joint sample of 38 Type~II SNe, which can be described as a skewed-Gaussian-like distribution between $0.005~M_{\odot}$ and $0.280~M_{\odot}$, with a median of $0.031~M_{\odot}$, mean of $0.046~M_{\odot}$, standard deviation of $0.048~M_{\odot}$ and skewness of $3.050$. We use two-sample Kolmogorov-Smirnov test and two-sample Anderson-Darling test to compare the observed distribution of $M_{\rm Ni}$ to results from theoretical hydrodynamical codes of core-collapse explosions with the neutrino mechanism presented in the literature. Our results show that the theoretical distributions obtained from the codes tested in this work, KEPLER and Prometheus Hot Bubble, are compatible with the observations irrespective of different pre-supernova calibrations and different maximum mass of the progenitors.

Tables

Table 1. Table 1 Supernovae and references

Supernova	Reference
SN 1992ba	Galbany et al. (2016);Gutiérrez et al. (2017a,b in prep.)
SN 2002gw	Galbany et al. (2016);Gutiérrez et al. (2017a,b in prep.)
SN 2003B	Galbany et al. (2016);Gutiérrez et al. (2017a,b in prep.)
SN 2003bn	Galbany et al. (2016);Gutiérrez et al. (2017a,b in prep.)
SN 2003E	Galbany et al. (2016);Gutiérrez et al. (2017a,b in prep.)
SN 2003ef	Galbany et al. (2016);Gutiérrez et al. (2017a,b in prep.)
SN 2003fb	Galbany et al. (2016);Gutiérrez et al. (2017a,b in prep.)
SN 2003hd	Galbany et al. (2016);Gutiérrez et al. (2017a,b in prep.)
SN 2003hn	Galbany et al. (2016);Gutiérrez et al. (2017a,b in prep.)
SN 2003ho	Galbany et al. (2016);Gutiérrez et al. (2017a,b in prep.)
SN 2003T	Galbany et al. (2016);Gutiérrez et al. (2017a,b in prep.)
SN 2009ib	Takáts et al. (2015)
SN 2012ec	Barbarino et al. (2015)
SN 2013ab	Bose et al. (2015)
SN 2013ej	Dhungana et al. (2015);Huang et al. (2015)
SN 2013fs	Childress et al. (2016);Smartt et al. (2015);
	Valenti et al. (2016);Yaron et al. (2017)
SN 2014G	Terreran et al. (2016)
ASASSN-14gm	Prieto et al. (2017, in prep.);Valenti et al. (2016)
ASASSN-14ha

Equations

$$\text{log}(E_{\exp }/10^{50}\text{ergs})=\alpha \cdot \text{b}+\eta$$

Full text

1. Introduction

Most massive stars with initial mass $M\gtrsim 8~{}M_{\odot}$ finish their lives with a collapse of their iron cores (e.g. Kalirai et al., 2008; Smartt, 2009; Smartt et al., 2009; Ibeling & Heger, 2013, but see also Zapartas et al. 2017 for the contribution of lower-mass stars in binary stars). A small fraction of the $\sim 10^{53}$ ergs of gravitational potential energy released in the collapse can power a core-collapse supernova (CCSN) explosion, leaving behind a neutron star or a black hole. A non-negligible fraction of massive stars might fail to explode as CCSN and instead relatively quietly collapse to a black hole (e.g., Nadezhin 1980; Burrows 1986; Liebendörfer et al. 2001; Heger et al. 2003; Kochanek et al. 2008; O’Connor & Ott 2011; Lovegrove & Woosley 2013; Kochanek 2014; Adams et al. 2016; although see also Kushnir & Katz 2015 for an alternative explosion model).

The most common kind of CCSNe are Type II supernovae (SN II) with broad spectral lines of hydrogen and plateau (SN II-P) light curves (e.g., Smith et al. 2011; Graur et al. 2017). The success of amateur and professional supernova surveys (e.g., Calán/Tololo, Hamuy et al. 1993; LOSS, Li et al. 2011; CHASE, Pignata et al. 2009; PTF/iPTF, Rau et al. 2009; Pan-Starrs, Kaiser et al. 2002; ASAS-SN, Shappee et al. 2014) has been paramount for follow-up studies that have uncovered the full range of observed and physical properties of normal SN II as well as significant correlations between some of their properties (e.g. Hamuy, 2003; Arcavi et al., 2012; Anderson et al., 2014; Faran et al., 2014; Gutiérrez et al., 2014; Sanders et al., 2015; Pejcha & Prieto, 2015a, b; Holoien et al., 2016; Valenti et al., 2016; Rubin et al., 2016). Hydrodynamical models of explosions of hydrogen-rich massive stars explain relatively well most of the main features of the light curves and spectra of normal SN II (e.g. Kasen & Woosley, 2009; Bersten et al., 2011; Dessart & Hillier, 2011; Pumo & Zampieri, 2011; Morozova et al., 2015; Lisakov et al., 2017).

Some of the CCSNe discoveries in nearby galaxies and the availability of deep pre-explosion images from HST and ground based 8-meter class telescopes have led to the detection of a number of massive star progenitors, most of them red super giants (RSG; e.g., Smartt, 2009, 2015). A confrontation of these detections and upper-limits with the expectations from a normal Salpeter stellar initial mass function (IMF; Salpeter 1955) constrains the main sequence progenitor masses of normal SN II to be $8\lesssim M\lesssim 18~{}M_{\odot}$ (e.g., Smartt, 2015). The relatively low upper limit in progenitor masses, compared to the local samples of RSG (e.g., Neugent et al., 2012; Massey & Evans, 2016), can be interpreted as evidence for failed explosions and black-hole formation above this mass. However, there remain other possible explanations and we need to seek a consistent picture encompassing not only the still limited set of progenitor detections, but also other constraints.

A substantial effort has been undertaken to understand the CCSN explosion mechanism with numerical simulations (e.g. Janka, 2012; Burrows, 2013; Bruenn et al., 2013; Couch, 2013; Ott, 2016, and references therein), but the ultimate goal has not been reached yet in part due to many complexities of the physics involved (e.g. Janka et al., 2016; Burrows, 2016). As a result, the community has been developing parameterized 1D explosion models that capture some of the most important aspects of the neutrino mechanism physics. Application of these models to a wide range of progenitors has revealed that successful and failed explosions depend critically on the internal structure of the progenitors (e.g. O’Connor & Ott, 2011; Ugliano et al., 2012; Pejcha & Thompson, 2015; Sukhbold et al., 2016), producing a more complicated picture than the traditional single progenitor mass cut for failed explosions and black-hole formation (e.g. Heger et al., 2003). These studies have also predicted the distributions of physical parameters of the supernova explosions, such as the asymptotic kinetic energies and masses of 56Ni synthesized in the explosions, which can lead to observational tests of the massive star progenitors and the explosion mechanism with complete samples of CCSNe.

In this paper, we study the physical parameters of a sample of well-observed, normal SN II, following the analysis by Pejcha & Prieto (2015a, b). We mainly focus on the observed 56Ni mass distribution and compare it with recent results from supernova explosion models. In Section 2, we present the data of the SN II used in this work. In Section 3, we briefly discuss the code used to fit the multicolor light curves and expansion velocity curves. In Section 4, we show the fits obtained from the code and the physical parameters. In Section 5, we discuss the completeness of our joint sample and focus on the nickel mass distribution. In Section 6, we compare theoretical nickel mass distributions with our observed distribution, where we found that the KEPLER and Prometheus Hot Bubble codes seem to match the observations.

2. Data

We studied a sub-sample of 11 normal SN II from the Calan-Tolo Supernova Program (Hamuy et al., 1993, C&T) and Carnegie Type II Supernova Survey (Galbany et al., 2016, CATS), with sufficient photometry in the optical UBVRI bands up to the nebular phase (Galbany et al., 2016) and spectra obtained at multiple epochs in the optical wavelength range (Gutiérrez et al. 2017a,b in preparation). We obtained expansion velocities from the SNe at different epochs by measuring the position of the minimum of the P-Cygni absorption trough of the Fe II line at rest-wavelength of 5169 Å, which is a good tracer of the photosphere (Takáts & Vinkó, 2012). The photometric measurements for SN 2003hn were supplemented with measurements from Krisciunas et al. (2008).

We added 8 more well-observed, normal SN II with data published in the literature: SN 2009ib (Takáts et al., 2015), SN 2012ec (Barbarino et al., 2015), SN 2013ab (Bose et al., 2015), SN 2013ej (Dhungana et al., 2015; Huang et al., 2015), SN 2013fs (Valenti et al., 2016; Childress et al., 2016; Smartt et al., 2015; Yaron et al., 2017), SN 2014G (Terreran et al., 2016), ASASSN-14gm/SN 2014cx (Valenti et al., 2016, Prieto et al. 2017, in prep.) and ASASSN-14ha (Childress et al., 2016; Valenti et al., 2016). Our final sample consists of 19 SN II. The SNe with their references for the data used in this paper are presented in Table 2.