Radiative-transfer modeling of nebular-phase type II supernovae

Nebular phase spectra of core-collapse supernovae (SNe) provide critical and unique information on the progenitor massive star and its explosion. We present a set of one-dimensional steady-state non-local thermodynamic equilibrium radiative transfer calculations of type II SNe at 300 d after explosion. Guided by the results obtained from a large set of stellar evolution simulations, we craft ejecta models for type II SNe from the explosion of a 12, 15, 20, and 25 M⊙ star. The ejecta density structure and kinetic energy, the 56Ni mass, and the level of chemical mixing are parametrized. Our model spectra are sensitive to the adopted line Doppler width, a phenomenon we associate with the overlap of Fe II and O I lines with Ly α and Ly β. Our spectra show a strong sensitivity to 56Ni mixing since it determines where decay power is absorbed. Even at 300 d after explosion, the H-rich layers reprocess the radiation from the inner metal rich layers. In a given progenitor model, variations in 56Ni mass and distribution impact the ejecta ionization, which can modulate the strength of all lines. Such ionization shifts can quench Ca II line emission. In our set of models, the [O I] λλ 6300, 6364 doublet strength is the most robust signature of progenitor mass. However, we emphasize that convective shell merging in the progenitor massive star interior can pollute the O-rich shell with Ca, which would weaken the O I doublet flux in the resulting nebular SN II spectrum. This process may occur in nature, with a greater occurrence in higher mass progenitors, and this may explain in part the preponderance of progenitor masses below 17 M⊙ that are inferred from nebular spectra.

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Spectral modeling of type II supernovae

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936137 ◽

2020 ◽

Vol 633 ◽

pp. A88 ◽

Cited By ~ 1

Author(s):

C. Vogl ◽

W. E. Kerzendorf ◽

S. A. Sim ◽

U. M. Noebauer ◽

S. Lietzau ◽

...

Keyword(s):

Radiative Transfer ◽

Large Data ◽

Training Dataset ◽

Parameter Study ◽

Type Ii ◽

Data Repositories ◽

Spectral Fitting ◽

Explosion Mechanism ◽

Radiative Transfer Modeling ◽

Good Agreement

There are now hundreds of publicly available supernova spectral time series. Radiative transfer modeling of this data provides insight into the physical properties of these explosions, such as the composition, the density structure, and the intrinsic luminosity, which is invaluable for understanding the supernova progenitors, the explosion mechanism, and for constraining the supernova distance. However, a detailed parameter study of the available data has been out of reach due to the high dimensionality of the problem coupled with the still significant computational expense. We tackle this issue through the use of machine-learning emulators, which are algorithms for high-dimensional interpolation. These use a pre-calculated training dataset to mimic the output of a complex code but with run times that are orders of magnitude shorter. We present the application of such an emulator to synthetic type II supernova spectra generated with the TARDIS radiative transfer code. The results show that with a relatively small training set of 780 spectra we can generate emulated spectra with interpolation uncertainties of less than one percent. We demonstrate the utility of this method by automatic spectral fitting of two well-known type IIP supernovae; as an exemplary application, we determine the supernova distances from the spectral fits using the tailored-expanding-photosphere method. We compare our results to previous studies and find good agreement. This suggests that emulation of TARDIS spectra can likely be used to perform automatic and detailed analysis of many transient classes putting the analysis of large data repositories within reach.

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Radiative-transfer modeling of supernovae in the nebular-phase

Astronomy and Astrophysics ◽

10.1051/0004-6361/202039287 ◽

2020 ◽

Vol 643 ◽

pp. L13

Author(s):

L. Dessart ◽

D. John Hillier

Keyword(s):

Radiative Transfer ◽

Line Emission ◽

Core Collapse ◽

Rapid Variation ◽

Simple Method ◽

Formidable Challenge ◽

Fluid Instabilities ◽

The Origin Of Life ◽

Radiative Transfer Modeling ◽

The Universe

Supernova (SN) explosions play a pivotal role in the chemical evolution of the Universe and the origin of life through the metals they release. Nebular phase spectroscopy constrains such metal yields, for example through forbidden line emission associated with O I, Ca II, Fe II, or Fe III. Fluid instabilities during the explosion produce a complex 3D ejecta structure, with considerable macroscopic, but no microscopic, mixing of elements. This structure sets a formidable challenge for detailed nonlocal thermodynamic equilibrium radiative transfer modeling, which is generally limited to 1D in grid-based codes. Here, we present a novel and simple method that allows for macroscopic mixing without any microscopic mixing, thereby capturing the essence of mixing in SN explosions. With this new technique, the macroscopically mixed ejecta are built by shuffling the shells from the unmixed coasting ejecta in mass space, or equivalently in velocity space. The method requires no change to the radiative transfer, but it necessitates high spatial resolution to resolve the rapid variation in composition with depth inherent to this shuffled-shell structure. We show the results for a few radiative-transfer simulations for a Type II SN explosion from a 15 M⊙ progenitor star. Our simulations capture the strong variations in temperature or ionization between the various shells that are rich in H, He, O, or Si. Because of nonlocal energy deposition, γ rays permeate through an extended region of the ejecta, making the details of the shell arrangement unimportant. The greater physical consistency of the method delivers spectral properties at nebular times that are more reliable, in particular in terms of individual emission line strengths, which may serve to constrain the SN yields as well as the progenitor mass for core collapse SNe. The method works for all SN types.

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The ALMA-PILS survey: 3D modeling of the envelope, disks and dust filament of IRAS 16293–2422

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731668 ◽

2018 ◽

Vol 612 ◽

pp. A72 ◽

Cited By ~ 25

Author(s):

S. K. Jacobsen ◽

J. K. Jørgensen ◽

M. H. D. van der Wiel ◽

H. Calcutt ◽

T. L. Bourke ◽

...

Keyword(s):

Radiative Transfer ◽

3D Model ◽

Line Emission ◽

Protoplanetary Disk ◽

Scale Height ◽

High Angular Resolution ◽

High Scale ◽

Disk Model ◽

Complex Morphology ◽

Radiative Transfer Modeling

Context. The Class 0 protostellar binary IRAS 16293–2422 is an interesting target for (sub)millimeter observations due to, both, the rich chemistry toward the two main components of the binary and its complex morphology. Its proximity to Earth allows the study of its physical and chemical structure on solar system scales using high angular resolution observations. Such data reveal a complex morphology that cannot be accounted for in traditional, spherical 1D models of the envelope. Aims. The purpose of this paper is to study the environment of the two components of the binary through 3D radiative transfer modeling and to compare with data from the Atacama Large Millimeter/submillimeter Array. Such comparisons can be used to constrain the protoplanetary disk structures, the luminosities of the two components of the binary and the chemistry of simple species. Methods. We present 13CO, C17O and C18O J = 3–2 observations from the ALMA Protostellar Interferometric Line Survey (PILS), together with a qualitative study of the dust and gas density distribution of IRAS 16293–2422. A 3D dust and gas model including disks and a dust filament between the two protostars is constructed which qualitatively reproduces the dust continuum and gas line emission. Results. Radiative transfer modeling in our sampled parameter space suggests that, while the disk around source A could not be constrained, the disk around source B has to be vertically extended. This puffed-up structure can be obtained with both a protoplanetary disk model with an unexpectedly high scale-height and with the density solution from an infalling, rotating collapse. Combined constraints on our 3D model, from observed dust continuum and CO isotopologue emission between the sources, corroborate that source A should be at least six times more luminous than source B. We also demonstrate that the volume of high-temperature regions where complex organic molecules arise is sensitive to whether or not the total luminosity is in a single radiation source or distributed into two sources, affecting the interpretation of earlier chemical modeling efforts of the IRAS 16293–2422 hot corino which used a single-source approximation. Conclusions. Radiative transfer modeling of source A and B, with the density solution of an infalling, rotating collapse or a protoplanetary disk model, can match the constraints for the disk-like emission around source A and B from the observed dust continuum and CO isotopologue gas emission. If a protoplanetary disk model is used around source B, it has to have an unusually high scale-height in order to reach the dust continuum peak emission value, while fulfilling the other observational constraints. Our 3D model requires source A to be much more luminous than source B; LA ~ 18 L⊙ and LB ~ 3 L⊙.

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PORTAL: Three-dimensional polarized (sub)millimeter line radiative transfer

Astronomy and Astrophysics ◽

10.1051/0004-6361/202037509 ◽

2020 ◽

Vol 636 ◽

pp. A14 ◽

Cited By ~ 4

Author(s):

Boy Lankhaar ◽

Wouter Vlemmings

Keyword(s):

Magnetic Field ◽

Radiative Transfer ◽

Three Dimensional ◽

Line Emission ◽

Local Anisotropy ◽

Alignment Mechanism ◽

Dimensional Simulation ◽

Regular Line ◽

Atomic States ◽

Radiative Transfer Modeling

Context. Magnetic fields are important to the dynamics of many astrophysical processes and can typically be studied through polarization observations. Polarimetric interferometry capabilities of modern (sub)millimeter telescope facilities have made it possible to obtain detailed velocity resolved maps of molecular line polarization. To properly analyze these for the information they carry regarding the magnetic field, the development of adaptive three-dimensional polarized line radiative transfer models is necessary. Aims. We aim to develop an easy-to-use program to simulate the polarization maps of molecular and atomic (sub)millimeter lines in magnetized astrophysical regions, such as protostellar disks, circumstellar envelopes, or molecular clouds. Methods. By considering the local anisotropy of the radiation field as the only alignment mechanism, we can model the alignment of molecular or atomic species inside a regular line radiative transfer simulation by only making use of the converged output of this simulation. Calculations of the aligned molecular or atomic states can subsequently be used to ray trace the polarized maps of the three-dimensional simulation. Results. We present a three-dimensional radiative transfer code, POlarized Radiative Transfer Adapted to Lines (PORTAL), that can simulate the emergence of polarization in line emission through a magnetic field of arbitrary morphology. Our model can be used in stand-alone mode, assuming LTE excitation, but it is best used when processing the output of regular three-dimensional (nonpolarized) line radiative transfer modeling codes. We present the spectral polarization map of test cases of a collapsing sphere and protoplanetary disk for multiple three-dimensional magnetic field morphologies.

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A magnetar model for the hydrogen-rich super-luminous supernova iPTF14hls

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732402 ◽

2018 ◽

Vol 610 ◽

pp. L10 ◽

Cited By ~ 18

Author(s):

Luc Dessart

Keyword(s):

Massive Star ◽

Type Ii ◽

Star Model ◽

Standard Type ◽

Bolometric Luminosity ◽

Typical Type ◽

Non Local ◽

Supergiant Star ◽

Optical Color ◽

Interesting Alternative

Transient surveys have recently revealed the existence of H-rich super-luminous supernovae (SLSN; e.g., iPTF14hls, OGLE-SN14-073) that are characterized by an exceptionally high time-integrated bolometric luminosity, a sustained blue optical color, and Doppler-broadened H I lines at all times. Here, I investigate the effect that a magnetar (with an initial rotational energy of 4 × 1050 erg and field strength of 7 × 1013 G) would have on the properties of a typical Type II supernova (SN) ejecta (mass of 13.35 M⊙, kinetic energy of 1.32 × 1051 erg, 0.077 M⊙ of 56Ni) produced by the terminal explosion of an H-rich blue supergiant star. I present a non-local thermodynamic equilibrium time-dependent radiative transfer simulation of the resulting photometric and spectroscopic evolution from 1 d until 600 d after explosion. With the magnetar power, the model luminosity and brightness are enhanced, the ejecta is hotter and more ionized everywhere, and the spectrum formation region is much more extended. This magnetar-powered SN ejecta reproduces most of the observed properties of SLSN iPTF14hls, including the sustained brightness of −18 mag in the R band, the blue optical color, and the broad H I lines for 600 d. The non-extreme magnetar properties, combined with the standard Type II SN ejecta properties, offer an interesting alternative to the pair-unstable super-massive star model recently proposed, which involves a highly energetic and super-massive ejecta. Hence, such Type II SLSNe may differ from standard Type II SNe exclusively through the influence of a magnetar.

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