Sub-Chandrasekhar progenitors favoured for type Ia supernovae: Evidence from late-time spectroscopy★.

Abstract A non-local-thermodynamic-equilibrium (NLTE) level population model of the first and second ionisation stages of iron, nickel and cobalt is used to fit a sample of XShooter optical + near-infrared (NIR) spectra of Type Ia supernovae (SNe Ia). From the ratio of the NIR lines to the optical lines limits can be placed on the temperature and density of the emission region. We find a similar evolution of these parameters across our sample. Using the evolution of the Fe ii 12 570 Å to 7 155 Å line as a prior in fits of spectra covering only the optical wavelengths we show that the 7200 Å feature is fully explained by [Fe ii] and [Ni ii] alone. This approach allows us to determine the abundance of Ni ii/Fe ii for a large sample of 130 optical spectra of 58 SNe Ia with uncertainties small enough to distinguish between Chandrasekhar mass (MCh) and sub-Chandrasekhar mass (sub-MCh) explosion models. We conclude that the majority (85%) of normal SNe Ia have a Ni/Fe abundance that is in agreement with predictions of sub-MCh explosion simulations of ∼Z⊙ progenitors. Only a small fraction (11%) of objects in the sample have a Ni/Fe abundance in agreement with MCh explosion models.

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Limits on stable iron in Type Ia supernovae from near-infrared spectroscopy

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833512 ◽

2018 ◽

Vol 620 ◽

pp. A200 ◽

Cited By ~ 2

Author(s):

A. Flörs ◽

J. Spyromilio ◽

K. Maguire ◽

S. Taubenberger ◽

W. E. Kerzendorf ◽

...

Keyword(s):

Near Infrared ◽

Type Ia Supernovae ◽

Near Infrared Spectra ◽

Theoretical Predictions ◽

Type Ia ◽

Iron Nickel ◽

Non Local ◽

Line Widths ◽

Measured Line ◽

Ia Supernovae

We obtained optical and near infrared spectra of Type Ia supernovae (SNe Ia) at epochs ranging from 224 to 496 days after the explosion. The spectra show emission lines from forbidden transitions of singly ionised iron and cobalt atoms. We used non-local thermodynamic equilibrium (NLTE) modelling of the first and second ionisation stages of iron, nickel, and cobalt to fit the spectra using a sampling algorithm allowing us to probe a broad parameter space. We derive velocity shifts, line widths, and abundance ratios for iron and cobalt. The measured line widths and velocity shifts of the singly ionised ions suggest a shared emitting region. Our data are fully compatible with radioactive 56Ni decay as the origin for cobalt and iron. We compare the measured abundance ratios of iron and cobalt to theoretical predictions of various SN Ia explosion models. These models include, in addition to 56Ni, different amounts of 57Ni and stable 54,56Fe. We can exclude models that produced only 54,56Fe or only 57Ni in addition to 56Ni. If we consider a model that has 56Ni, 57Ni, and 54,56Fe then our data imply that these ratios are 54,56Fe / 56Ni = 0.272 ± 0.086 and 57Ni / 56Ni = 0.032 ± 0.011.

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Understanding nebular spectra of Type Ia supernovae

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa640 ◽

2020 ◽

Vol 494 (2) ◽

pp. 2221-2235 ◽

Cited By ~ 2

Author(s):

Kevin D Wilk ◽

D John Hillier ◽

Luc Dessart

Keyword(s):

Radiative Transfer ◽

Local Thermodynamic Equilibrium ◽

Diagnostic Feature ◽

Type Ia Supernovae ◽

Thermal Heating ◽

One Dimensional ◽

Type Ia ◽

Natural Mechanism ◽

Non Local ◽

Ia Supernovae

ABSTRACT In this study, we present one-dimensional, non-local-thermodynamic-equilibrium, radiative transfer simulations (using cmfgen) in which we introduce micro-clumping at nebular times into two Type Ia supernova ejecta models. We use one sub-Chandrasekhar (sub-MCh) ejecta model with 1.04 M⊙ and one Chandrasekhar (MCh) ejecta model with 1.40 M⊙. We introduce clumping factors f = 0.33, 0.25, and 0.10, which are constant throughout the ejecta, and compare results to the unclumped f = 1.0 case. We find that clumping is a natural mechanism to reduce the ionization of the ejecta, reducing emission from [Fe iii], [Ar iii], and [S iii] by a factor of a few. For decreasing values of the clumping factor f, the [Ca ii] λλ7291,7324 doublet became a dominant cooling line for our MCh model but remained weak in our sub-MCh model. Strong [Ca ii] λλ7291,7324 indicates non-thermal heating in that region and may constrain explosion modelling. Due to the low abundance of stable nickel, our sub-MCh model never showed the [Ni ii] 1.939-μm diagnostic feature for all clumping values.

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Late-time emission of type Ia supernovae: optical and near-infrared observations of SN 2001el

Astronomy and Astrophysics ◽

10.1051/0004-6361:20066999 ◽

2007 ◽

Vol 470 (1) ◽

pp. L1-L4 ◽

Cited By ~ 33

Author(s):

M. Stritzinger ◽

J. Sollerman

Keyword(s):

Near Infrared ◽

Type Ia Supernovae ◽

Late Time ◽

Infrared Observations ◽

Type Ia ◽

Ia Supernovae

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A year-long plateau in the late-time near-infrared light curves of type Ia supernovae

Nature Astronomy ◽

10.1038/s41550-019-0901-1 ◽

2019 ◽

Vol 4 (2) ◽

pp. 188-195 ◽

Cited By ~ 1

Author(s):

O. Graur ◽

K. Maguire ◽

R. Ryan ◽

M. Nicholl ◽

A. Avelino ◽

...

Keyword(s):

Near Infrared ◽

Light Curves ◽

Infrared Light ◽

Type Ia Supernovae ◽

Late Time ◽

Near Infrared Light ◽

Type Ia ◽

Ia Supernovae

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Constraints on the density distribution of type Ia supernovae ejecta inferred from late-time light-curve flattening

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa690 ◽

2020 ◽

Vol 493 (4) ◽

pp. 5617-5624

Author(s):

Doron Kushnir ◽

Eli Waxman

Keyword(s):

Light Curve ◽

Weighted Average ◽

Far Infrared ◽

Average Density ◽

Light Curves ◽

Type Ia Supernovae ◽

Late Time ◽

Simple Method ◽

Type Ia ◽

Ia Supernovae

ABSTRACT The finite time, τdep, over which positrons from β+ decays of 56Co deposit energy in type Ia supernovae ejecta lead, in case the positrons are trapped, to a slower decay of the bolometric luminosity compared to an exponential decline. Significant light-curve flattening is obtained when the ejecta density drops below the value for which τdep equals the 56Co lifetime. We provide a simple method to accurately describe this ‘delayed deposition’ effect, which is straightforward to use for analysis of observed light curves. We find that the ejecta heating is dominated by delayed deposition typically from 600 to 1200 d, and only later by longer lived isotopes 57Co and 55Fe decay (assuming solar abundance). For the relatively narrow 56Ni velocity distributions of commonly studied explosion models, the modification of the light curve depends mainly on the 56Ni mass-weighted average density, 〈ρ〉t3. Accurate late-time bolometric light curves, which may be obtained with JWST far-infrared (far-IR) measurements, will thus enable to discriminate between explosion models by determining 〈ρ〉t3 (and the 57Co and 55Fe abundances). The flattening of light curves inferred from recent observations, which is uncertain due to the lack of far-IR data, is readily explained by delayed deposition in models with $\langle \rho \rangle t^{3} \approx 0.2\, \mathrm{M}_{\odot }\, (10^{4}\, \textrm{km}\, \textrm{s}^{-1})^{-3}$, and does not imply supersolar 57Co and 55Fe abundances.

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Monte Carlo radiative transfer for the nebular phase of Type Ia supernovae

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3412 ◽

2019 ◽

Vol 492 (2) ◽

pp. 2029-2043 ◽

Cited By ~ 2

Author(s):

L J Shingles ◽

S A Sim ◽

M Kromer ◽

K Maguire ◽

M Bulla ◽

...

Keyword(s):

Radiative Transfer ◽

Atomic Data ◽

Type Ia Supernovae ◽

Data Set ◽

High Ionization ◽

Type Ia ◽

Non Local ◽

Ionization Balance ◽

Ia Supernovae ◽

Modest Effect

ABSTRACT We extend the range of validity of the artis 3D radiative transfer code up to hundreds of days after explosion, when Type Ia supernovae (SNe Ia) are in their nebular phase. To achieve this, we add a non-local thermodynamic equilibrium population and ionization solver, a new multifrequency radiation field model, and a new atomic data set with forbidden transitions. We treat collisions with non-thermal leptons resulting from nuclear decays to account for their contribution to excitation, ionization, and heating. We validate our method with a variety of tests including comparing our synthetic nebular spectra for the well-known one-dimensional W7 model with the results of other studies. As an illustrative application of the code, we present synthetic nebular spectra for the detonation of a sub-Chandrasekhar white dwarf (WD) in which the possible effects of gravitational settling of 22Ne prior to explosion have been explored. Specifically, we compare synthetic nebular spectra for a 1.06 M⊙ WD model obtained when 5.5 Gyr of very efficient settling is assumed to a similar model without settling. We find that this degree of 22Ne settling has only a modest effect on the resulting nebular spectra due to increased 58Ni abundance. Due to the high ionization in sub-Chandrasekhar models, the nebular [Ni ii] emission remains negligible, while the [Ni iii] line strengths are increased and the overall ionization balance is slightly lowered in the model with 22Ne settling. In common with previous studies of sub-Chandrasekhar models at nebular epochs, these models overproduce [Fe iii] emission relative to [Fe ii] in comparison to observations of normal SNe Ia.

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