We present numerical simulations that include 1D Eulerian multigroup radiation-hydrodynamics, 1D non-local thermodynamic equilibrium (non-LTE) radiative transfer, and 2D polarized radiative transfer ...for superluminous interacting supernovae (SNe). Our reference model is a ∼10 M⊙ inner shell with 1051 erg ramming into an ∼3 M⊙ cold outer shell (the circumstellar medium, or CSM) that extends from 1015 to 2 × 1016 cm and moves at 100 km s−1. We discuss the light-curve evolution, which cannot be captured adequately with a grey approach. In this type of interactions, the shock-crossing time through the optically thick CSM is much longer than the photon diffusion time. Radiation is thus continuously leaking from the shock through the CSM. This configuration is distinct from the shell-shocked model. Our spectra redden with time, with a peak distribution in the near-UV during the first month gradually shifting to the optical range over the following year. Initially, Balmer lines exhibit a narrow line core and the broad line wings that are characteristic of electron scattering in the SNe IIn atmospheres (CSM). At later times, they also exhibit a broad blue-shifted component which arises from the cold dense shell. Our model results are broadly consistent with the bolometric light curve and spectral evolution observed for SN 2010jl. Invoking a prolate pole-to-equator density ratio in the CSM, we can also reproduce the ∼2 per cent continuum polarization, and line depolarization, observed in SN 2010jl. By varying the inner shell kinetic energy and the mass and extent of the outer shell, a large range of peak luminosities and durations, broadly compatible with superluminous SNe IIn like 2010jl or 2006gy, can be produced.
Early-time observations of Type II supernovae (SNe) 2013cu and 2013fs have revealed an interaction of ejecta with material near the star surface. Unlike Type IIn SN 2010jl, which interacts with a ...dense wind for ~1 yr, the interaction ebbs after 2–3 d, suggesting a dense and compact circumstellar envelope. Here, we use multi-group radiation hydrodynamics and non-local-thermodynamic-equilibrium radiative transfer to explore the properties of red-supergiant (RSG) star explosions embedded in a variety of dense envelopes. We consider the cases of an extended static atmosphere or a steady-state wind, adopting a range of mass loss rates. The shock breakout signal, luminosity and color evolution up to 10 d, and ejecta dynamics are strongly influenced by the properties of this nearby environment. This compromises the use of early-time observations to constrain R⋆. For dense circumstellar envelopes, the time-integrated luminosity over the first 10−15 d can be boosted by a factor of a few. The presence of narrow lines for 2–3 d in 2013fs and 2013cu require a cocoon of material of ~0.01 M⊙ out to 5−10 R⋆. Spectral lines evolve from electron scattering to Doppler broadened with a growing blueshift of their emission peaks. Recent studies propose a super-wind phase with a mass loss rate from 0.001 up to 1 M⊙ yr-1 in the last months or years of the life of a RSG, although there is no observational constraint that this external material is a steady-state outflow. Alternatively, observations may be explained by the explosion of a RSG star inside its complex atmosphere. Indeed, spatially resolved observations reveal that RSG stars have extended atmospheres, with the presence of downflows and upflows out to several R⋆, even in a standard RSG such as Betelgeuse. Mass loading in the region intermediate between star and wind can accommodate the 0.01 M⊙ needed to explain the observations of 2013fs. Signatures of interaction in early-time spectra of RSG star explosions may therefore be the norm, not the exception, and a puzzling super-wind phase prior to core collapse may be superfluous.
Because mass loss is a fundamental phenomenon in massive stars, an interaction with circumstellar material (CSM) should be universal in core-collapse supernovae (SNe). Leaving aside the extreme CSM ...density, extent, or mass typically encountered in Type IIn SNe, we investigate the diverse long-term radiative signatures of an interaction between a Type II SN ejecta and CSM corresponding to mass-loss rates up to 10
−3
M
⊙
yr
−1
. Because these CSM are relatively tenuous and optically thin to electron scattering beyond a few stellar radii, radiation hydrodynamics is not essential and one may treat the interaction directly as an additional power source in the non-local thermodynamic equilibrium radiative transfer problem. The CSM accumulated since shock breakout forms a dense shell in the outer ejecta and leads to high-velocity absorption features in spectral lines, even for a negligible shock power. In addition to Balmer lines, such features may appear in Na
I
D and He
I
lines, among others. A stronger interaction strengthens the continuum flux (preferentially in the UV), quenches the absorption of P-Cygni profiles, boosts the Mg
II
λλ
2795, 2802 doublet, and fosters the production of a broad-boxy H
α
emission component. The rise in ionization in the outer ejecta may quench some lines (e.g., the Ca
II
near-infrared triplet). The interaction power emerges preferentially in the UV, in particular at later times, shifting the optical color to the blue, but increasing the optical luminosity modestly. Strong thermalization and clumping seem to be required to make an interaction superluminous in the optical. The UV range contains essential signatures that provide critical constraints to infer the mass-loss history and inner workings of core-collapse SN progenitors at death.
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.
We present non-local thermodynamic equilibrium time-dependent radiative transfer simulations of pair-instability supernovae (PISNe) stemming from red-supergiant (RSG), blue-supergiant and Wolf-Rayet ...star rotation-free progenitors born in the mass range 160-230 M, at 10−4 Z. Although subject to uncertainties in convection and stellar mass-loss rates, our initial conditions come from physically-consistent models that treat evolution from the main sequence, the onset of the pair-production instability, and the explosion phase. With our set of input models characterized by large 56Ni and ejecta masses, and large kinetic energies, we recover qualitatively the Type II-Plateau, II-peculiar and Ib/c light-curve morphologies, although they have larger peak bolometric luminosities (∼109 to 1010 L) and a longer duration (∼200 d). We discuss the spectral properties for each model during the photospheric and nebular phases, including Balmer lines in II-P and II-pec at early times, the dominance of lines from intermediate-mass elements near the bolometric maximum, and the strengthening of metal line blanketing thereafter. Having similar He-core properties, all models exhibit similar post-peak spectra that are strongly blanketed by Fe ii and Fe i lines, characterized by red colours, and that arise from photospheres/ejecta with a temperature of 4000 K. Combined with the modest linewidths after the bolometric peak, these properties contrast with those of known superluminous SNe, suggesting that PISNe are yet to be discovered. Being reddish, PISNe will be difficult to observe at high redshift except when they stem from RSG explosions, in which case they could be used as metallicity probes and distance indicators.
Abstract
While Chandrasekhar-mass (MCh) models with a low 56Ni yield can match the peak luminosities of fast-declining, 91bg-like Type Ia supernovae (SNe Ia), they systematically fail to reproduce ...their faster light-curve evolution. Here, we illustrate the impact of a low ejecta mass on the radiative display of low-luminosity SNe Ia, by comparing a sub-MCh model resulting from the pure central detonation of a C-O white dwarf (WD) to an MCh delayed-detonation model with the same 56Ni yield of 0.12 M⊙. Our sub-MCh model from a 0.90 M⊙ WD progenitor has a ∼5 d shorter rise time in the integrated UV–optical–IR (uvoir) luminosity, as well as in the B band, and a ∼20 per cent higher peak uvoir luminosity (∼1 mag brighter peak MB). This sub-MCh model also displays bluer maximum-light colours due to the larger specific heating rate, and larger post-maximum uvoir and B-band decline rates. The luminosity decline at nebular times is also more pronounced, reflecting the enhanced escape of gamma rays resulting from the lower density of the progenitor WD. The deficit of stable nickel in the innermost ejecta leads to a notable absence of forbidden lines of Ni ii in the nebular spectra. In contrast, the MCh model displays a strong line due to Ni ii 1.939 μm, which could in principle serve to distinguish between different progenitor scenarios. Our sub-MCh model offers an unprecedented agreement with optical and near-infrared observations of the 91bg-like SN 1999by, making a strong case for a WD progenitor significantly below the Chandrasekhar-mass limit for this event and other low-luminosity SNe Ia.
Type Ibn supernovae (SNe) are a mysterious class of transients whose spectra exhibit persistently narrow He
I
lines, and whose bolometric light curves are typically fast evolving and overluminous at ...peak relative to standard Type Ibc SNe. We explore the interaction scenario of such Type Ibn SNe by performing radiation-hydrodynamics and radiative-transfer calculations. We find that standard-energy helium-star explosions within dense wind-like circumstellar material (CSM) can reach a peak luminosity of a few 10
44
erg s
−1
on day timescales, which is reminiscent of exceptional events such as AT 2018cow. Similar interactions but with weaker winds can lead to Type Ibc SNe with double-peak light curves and peak luminosities in the range ∼10
42.2
to ∼10
43
erg s
−1
. In contrast, the narrow spectral lines and modest peak luminosities of most Type Ibn SNe are suggestive of a low-energy explosion in an initially ≲5
M
⊙
helium star, most likely arising from interacting binaries and colliding with a massive helium-rich, probably ejecta-like, CSM at ∼10
15
cm. Nonlocal thermodynamic equilibrium radiative-transfer simulations of a slow-moving dense shell born out and powered by the interaction compare favorably to Type Ibn SNe such as 2006jc, 2011hw, or 2018bcc at late times and suggest a composition made of about 50% helium, a solar metallicity, and a total ejecta and CSM mass of 1–2
M
⊙
. A lower fractional helium abundance leads to weak or absent He
I
lines and thus excludes more massive configurations for observed Type Ibn SNe. Further, the dominance of Fe
II
emission below 5500 Å seen in Type Ibn SNe at late times is not predicted at low metallicity. Hence, despite their promising properties, Type Ibn SNe from a pulsational-pair instability in very massive stars, requiring low metallicity, probably have not been observed yet.
Much controversy surrounds the inferred progenitor masses of type-II-Plateau (II-P) supernovae (SNe). The debate is nourished by the discrepant results from radiation-hydrodynamics simulations, ...pre-explosion imaging, and studies of host stellar populations. Here, we present a controlled experiment using four solar-metallicity models with zero-age main sequence masses of 12, 15, 20, and 25 M⊙. Because of the effects of core burning and surface mass loss, these models reach core collapse as red-supergiant (RSG) stars with a similar H-rich envelope mass of 8 to 9 M⊙ but with final masses in the range 11 to 16 M⊙. We explode the progenitors using a thermal bomb, adjusting the energy deposition to yield an asymptotic ejecta kinetic energy of 1.25 × 1051 erg and an initial 56Ni mass of 0.04 M⊙. The resulting SNe produce similar photometric and spectroscopic properties from 10 to 200 d. The spectral characteristics are degenerate. The scatter in early-time color results from the range in progenitor radii, while the differences in late-time spectra reflect the larger oxygen yields in more massive progenitors. Because the progenitors have a comparable H-rich envelope mass, the photospheric phase duration is comparable for all models; the difference in He-core mass is invisible. As different main sequence masses can produce progenitors with a similar H-rich envelope mass, light-curve modeling cannot provide a robust and unique solution for the ejecta mass of type-II-P SNe. The numerous uncertainties in massive-star evolution and wind-mass loss also prevent a robust association with a main sequence star mass. Light-curve modeling can at best propose compatibility.
Abstract
Supernova (SN) 2008bk is a well-observed low-luminosity Type II event visually associated with a low-mass red-supergiant progenitor. To model SN 2008bk, we evolve a 12 M⊙ star from the main ...sequence until core collapse, when it has a total mass of 9.88 M⊙, a He-core mass of 3.22 M⊙ and a radius of 502 R⊙. We then artificially trigger an explosion that produces 8.29 M⊙ of ejecta with a total energy of 2.5 × 1050 erg and ∼0.009 M⊙ of 56Ni. We model the subsequent evolution of the ejecta with non-local thermodynamic equilibrium time-dependent radiative transfer. Although somewhat too luminous and energetic, this model reproduces satisfactorily the multiband light curves and multi-epoch spectra of SN 2008bk, confirming the suitability of a low-mass massive star progenitor. As in other low-luminosity SNe II, the structured Hα profile at the end of the plateau phase is probably caused by Ba ii 6496.9 Å rather than asphericity. We discuss the sensitivity of our results to changes in progenitor radius and mass, as well as chemical mixing. A 15 per cent increase in progenitor radius causes a 15 per cent increase in luminosity and a 0.2 mag V-band brightening of the plateau but leaves its length unaffected. An increase in ejecta mass by 10 per cent lengthens the plateau by ∼10 d. Chemical mixing introduces slight changes to the bolometric light curve, limited to the end of the plateau, but has a large impact on colours and spectra at nebular times.
Using radiation hydrodynamics and radiative transfer simulations, we explore the origin of the spectral diversity of interacting supernovae (SNe) of Type IIn. We revisit SN 1994W and investigate the ...dynamical configurations that can give rise to spectra with narrow lines at all times. We find that a standard ∼10 M⊙ 1051 erg SN ejecta ramming into a 0.4 M⊙ dense circumstellar material is inadequate for SN 1994W, as it leads to the appearance of broad lines at late times. This structure, however, generates spectra that exhibit the key morphological changes seen in SN 1998S. For SN 1994W, we consider a completely different configuration, which involves the interaction at a large radius of a low-mass inner shell with a high-mass outer shell. Such a structure may arise in an 8–12 M⊙ star from a nuclear flash (e.g. of Ne) followed within a few years by core collapse. Our simulations show that the large mass of the outer shell leads to the complete braking of the inner shell material, the formation of a slow dense shell, and the powering of a luminous SN IIn, even for a low inner shell energy. Early on, our model line profiles are typical of SNe IIn, exhibiting narrow cores and broad electron-scattering wings. As observed in SN 1994W, they also remain narrow at late times. Our SN 1994W model invokes two low-energy ejections, both atypical of observed massive stars, and illustrates the diversity of configurations leading to SNe IIn. These results also highlight the importance of spectra to constrain the dynamical properties and understand the origin of SNe IIn.
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