scholarly journals Understanding nebular spectra of Type Ia supernovae

2020 ◽  
Vol 494 (2) ◽  
pp. 2221-2235 ◽  
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.

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

2019 ◽  
Vol 492 (2) ◽  
pp. 2029-2043 ◽  
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.

scholarly journals An asymmetric explosion mechanism may explain the diversity of Si ii linewidths in Type Ia supernovae

2020 ◽  
Vol 494 (4) ◽  
pp. 5811-5824
Author(s):  
Ran Livneh ◽  
Boaz Katz
Keyword(s):  
Radiative Transfer ◽  
Thermodynamic Equilibrium ◽  
Local Thermodynamic Equilibrium ◽  
Spectral Feature ◽  
Type Ia Supernovae ◽  
Absorption Region ◽  
Type Ia ◽  
Order Of Magnitude ◽  
Good Tracer ◽  
Ia Supernovae

ABSTRACT Near maximum brightness, the spectra of Type Ia supernovae (SNe Ia) present typical absorption features of Silicon II observed at roughly $6100$ and $5750\, \mathring{\rm A}$. The two-dimensional distribution of the pseudo-equivalent widths (pEWs) of these features is a useful tool for classifying SNe Ia spectra (Branch plot). Comparing the observed distribution of SNe on the Branch plot to results of simulated explosion models, we find that one-dimensional models fail to cover most of the distribution. In contrast, we find that tardis radiative transfer simulations of the white dwarf head-on collision models along different lines of sight almost fully cover the distribution. We use several simplified approaches to explain this result. We perform order-of-magnitude analysis and model the opacity of the Si ii lines using local thermodynamic equilibrium and non-local thermodynamic equilibrium approximations. Introducing a simple toy model of spectral feature formation, we show that the pEW is a good tracer for the extent of the absorption region in the ejecta. Using radiative transfer simulations of synthetic SN ejecta, we reproduce the observed Branch plot distribution by varying the luminosity of the SN and the Si density profile of the ejecta. We deduce that the success of the collision model in covering the Branch plot is a result of its asymmetry, which allows for a significant range of Si density profiles along different viewing angles, uncorrelated with a range of 56Ni yields that cover the observed range of SN Ia luminosity. We use our results to explain the shape and boundaries of the Branch plot distribution.

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

2019 ◽  
Author(s):  
A Flörs ◽  
J Spyromilio ◽  
S Taubenberger ◽  
S Blondin ◽  
R Cartier ◽  
...  
Keyword(s):  
Near Infrared ◽  
Local Thermodynamic Equilibrium ◽  
Emission Region ◽  
Type Ia Supernovae ◽  
Late Time ◽  
Type Ia ◽  
Iron Nickel ◽  
Non Local ◽  
Optical Wavelengths ◽  
Ia Supernovae

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.

scholarly journals One-dimensional delayed-detonation models of Type Ia supernovae: confrontation to observations at bolometric maximum

2012 ◽  
Vol 429 (3) ◽  
pp. 2127-2142 ◽  
Author(s):  
Stéphane Blondin ◽  
Luc Dessart ◽  
D. John Hillier ◽  
Alexei M. Khokhlov
Keyword(s):  
Type Ia Supernovae ◽  
One Dimensional ◽  
Type Ia ◽  
Ia Supernovae

scholarly journals Light Curve Models for SN 2009dc

2011 ◽  
Vol 7 (S281) ◽  
pp. 314-315
Author(s):  
Yasuomi Kamiya
Keyword(s):  
Light Curve ◽  
White Dwarfs ◽  
Light Curves ◽  
Host Galaxy ◽  
Type Ia Supernovae ◽  
Radiation Hydrodynamics ◽  
One Dimensional ◽  
Type Ia ◽  
Ia Supernovae

AbstractSimplified explosion models of super-Chandrasekhar-mass C-O white dwarfs (WDs) are constructed with parameters such as WD mass and 56Ni mass. Their light curves are obtained by solving one-dimensional equations of radiation hydrodynamics, and compared with the observations of SN 2009dc, one of the overluminous Type Ia supernovae, to estimate its properties. As a result, the progenitor of SN 2009dc is suggested to be a 2.2–2.4-M⊙ C-O WD with 1.2–1.4 M⊙ of 56Ni, if the extinction by its host galaxy is negligible.

scholarly journals The accuracy of post-processed nucleosynthesis

2020 ◽  
Vol 494 (2) ◽  
pp. 3037-3047
Author(s):  
Eduardo Bravo
Keyword(s):  
Nuclear Energy ◽  
Abundant Species ◽  
Type Ia Supernovae ◽  
Post Processing ◽  
One Dimensional ◽  
Type Ia ◽  
Order Of Magnitude ◽  
Stable Elements ◽  
Ia Supernovae ◽  
Better Than

ABSTRACT The computational requirements posed by multi-dimensional simulations of type Ia supernovae make it difficult to incorporate complex nuclear networks to follow the release of nuclear energy along with the propagation of the flame. Instead, these codes usually model the flame and use simplified nuclear kinetics, with the goal of determining a sufficiently accurate rate of nuclear energy generation and, afterwards, post-processing the thermodynamic trajectories with a large nuclear network to obtain more reliable nuclear yields. In this work, I study the performance of simplified nuclear networks with respect to reproduction of the nuclear yields obtained with a one-dimensional supernova code equipped with a large nuclear network. I start by defining a strategy to follow the properties of matter in nuclear statistical equilibrium (NSE). I propose to use published tables of NSE properties, together with a careful interpolation routine. Short networks (iso7 and 13α) are able to give an accurate yield of 56Ni, after post-processing, but can fail by order of magnitude in predicting the ejected mass of even mildly abundant species (>10−3 M⊙). A network of 21 species reproduces the nucleosynthesis of the Chandrasekhar and sub-Chandrasekhar explosions studied here with average errors better than 20 per cent for the whole set of stable elements and isotopes followed in the models.

scholarly journals Spectral signatures of H-rich material stripped from a non-degenerate companion by a Type Ia supernova

2020 ◽  
Vol 638 ◽  
pp. A80 ◽  
Author(s):  
Luc Dessart ◽  
Douglas C. Leonard ◽  
Jose L. Prieto
Keyword(s):  
Equivalent Width ◽  
Giant Planet ◽  
Type Ia Supernovae ◽  
Circumstellar Material ◽  
Type Ia ◽  
Balmer Lines ◽  
Non Local ◽  
Hydrodynamical Simulations ◽  
Rich Material ◽  
Ia Supernovae

The single-degenerate scenario for Type Ia supernovae should yield metal-rich ejecta that enclose some stripped material from the non-degenerate H-rich companion star. We present a large grid of non-local thermodynamic equilibrium steady-state radiative transfer calculations for such hybrid ejecta and provide analytical fits for the Hα luminosity and equivalent width. Our set of models covers a range of masses for 56Ni and the ejecta, for the stripped material (Mst), and post-explosion epochs from 100 to 300 d. The brightness contrast between stripped material and metal-rich ejecta challenges the detection of H I and He I lines prior to ~100 d. Intrinsic and extrinsic optical depth effects also influence the radiation emanating from the stripped material. This inner denser region is marginally thick in the continuum and optically thick in all Balmer lines. The overlying metal-rich ejecta blanket the inner regions, completely below about 5000 Å, and more sparsely at longer wavelengths. As a consequence, Hβ should not be observed for all values of Mst up to at least 300 days, while Hα should be observed after ~100 d for all Mst ≥ 0.01 M⊙. Observational non-detections capable of limiting the Hα equivalent width to <1 Å set a formal upper limit of Mst < 0.001M⊙. This contrasts with the case of circumstellar-material (CSM) interaction, not subject to external blanketing, which should produce Hα and Hβ lines with a strength dependent primarily on CSM density. We confirm previous analyses that suggest low values of order 0.001 M⊙ for Mst to explain the observations of the two Type Ia supernovae with nebular-phase Hα detection, in conflict with the much greater stripped mass predicted by hydrodynamical simulations for the single-degenerate scenario. A more likely solution is the double-degenerate scenario, together with CSM interaction, or enclosed material from a tertiary star in a triple system or from a giant planet.

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