Supernovae Ia in 2019 (review): a rising demand for spherical explosions

We present an analysis of the light curve (LC) decline rates $(\Delta m_{15})$ of 407 normal and peculiar supernovae (SNe) Ia and global parameters of their host galaxies. As previously known, there is a significant correlation between the $\Delta m_{15}$ of normal SNe Ia and global ages (morphologies, colours, masses) of their hosts. On average, those normal SNe Ia that are in galaxies from the Red Sequence (early-type, massive, old hosts) have faster declining LCs in comparison with those from the Blue Cloud (late-type, less massive, younger hosts) of the colour-mass diagram. The observed correlations between the $\Delta m_{15}$ of normal SNe Ia and hosts' parameters appear to be due to the superposition of at least two distinct populations of faster and slower declining normal SNe Ia from older and younger stellar components. We show, for the first time, that the $\Delta m_{15}$ of 91bg- and 91T-like SNe is independent of host morphology and colour. The distribution of hosts on the colour-mass diagram confirms the known tendency for 91bg-like SNe to occur in globally red/old galaxies while 91T-like events prefer blue/younger hosts. On average, the youngest global ages of 02cx-like SNe hosts and their positions in the colour-mass diagram hint that these events likely originate from young population, but they differ from 91T-like events in the LC decline rate. Finally, we discuss the possible explosion channels and present our favoured SN Ia models that have the potential to explain the observed SN-host relations.

Supernovae and their host galaxies - VII. The diversity of Type Ia supernova progenitors

The observed diversity in Type Ia supernovae (SNe Ia) – the thermonuclear explosions of carbon-oxygen white dwarf stars used as cosmological standard candles – is currently met with a variety of explosion models and progenitor scenarios. To help improve our understanding of whether and how often different models contribute to the occurrence of SNe Ia and their assorted properties, we present a comprehensive analysis of seven nearby SNe Ia. We obtained one to two epochs of optical spectra with Gemini Observatory during the nebular phase (>200 days past peak) for each of these events, all of which had time-series of photometry and spectroscopy at early times (the first ∼8 weeks after explosion). We use the combination of earlyand late-time observations to assess the predictions of various models for the explosion (e.g., double-detonation, off-center detonation, stellar collisions), progenitor star (e.g., ejecta mass, metallicity), and binary companion (e.g., another white dwarf or a non-degenerate star). Overall, we find general consistency in our observations with spherically-symmetric models for SN Ia explosions, and with scenarios in which the binary companion is another degenerate star. We also present an in-depth analysis of SN 2017fzw, a member of the sub-group of SNe Ia which appear to be transitional between the subluminous “91bg-like" events and normal SNe Ia, and for which nebular-phase spectra are rare.

/pdf/nebular-phase-spectra-of-type-ia-supernovae-from-the-las-2jbuowtt.pdf

Nebular-Phase Spectra of Type Ia Supernovae from the Las Cumbres Observatory Global Supernova Project

We infer initial masses of the synthesized radioactive nickel-56 in a sample of recent Type Ia supernovae applying a new formalism introduced recently by Khatami & Kasen. It is shown that the nickel masses we derive do not differ significantly from previous estimates based on the traditional Arnett-model. We derive the β parameter for our sample SNe and show that these are consistent with the fiducial value of ∼1.6 given by Khatami & Kasen from SN Ia hydrodynamical simulations.

Initial Ni-56 Masses in Type Ia Supernovae

We present the optical (UBVRI) and ultraviolet (Swift-UVOT) photometry, and optical spectroscopy of Type Ia supernova SN 2017hpa. We study broadband UV+optical light curves and low resolution spectroscopy spanning from $-13.8$ to $+108$~d from the maximum light in $B$-band. The photometric analysis indicates that SN 2017hpa is a normal type Ia with $\Delta m_{B}(15) = 0.98\pm0.16$ mag and $M_{B}=-19.45\pm0.15$ mag at a distance modulus of $\mu = 34.08\pm0.09$ mag. The $(uvw1-uvv)$ colour evolution shows that SN 2017hpa falls in the NUV-blue group. The $(B-V)$ colour at maximum is bluer in comparison to normal type Ia supernovae. Spectroscopic analysis shows that the Si II 6355 absorption feature evolves rapidly with a velocity gradient, $\dot{v}=128\pm 7$ km s$^{-1}$ d$^{-1}$. The pre-maximum phase spectra show prominent C II 6580 {\AA} absorption feature. The C II 6580 {\AA} line velocity measured from the observed spectra is lower than the velocity of Si II 6355 {\AA}, which could be due to a line of sight effect. The synthetic spectral fits to the pre-maximum spectra using syn++ indicate the presence of a high velocity component in the Si II absorption, in addition to a photospheric component. Fitting the observed spectrum with the spectral synthesis code TARDIS, the mass of unburned C in the ejecta is estimated to be $\sim 0.019$~$M_{\odot}$. The peak bolometric luminosity is $L^{bol}_{peak} = 1.43\times10^{43}$ erg s$^{-1}$. The radiation diffusion model fit to the bolometric light curve indicates $0.61\pm0.02$ $M_\odot$ of $^{56}$Ni is synthesized in the explosion.

SN 2017hpa: a carbon-rich Type Ia supernova

Constraints on the Physical Properties of SNe Ia from Photometry

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Constraints on the Physical Properties of SNe Ia from Photometry