Core-collapse Supernova Events Research Articles

Determining the Core Structure and Nuclear Equation of State of Rotating Core-collapse Supernovae with Gravitational Waves by Convolutional Neural Networks

Detecting gravitational waves from a nearby core-collapse supernova would place meaningful constraints on the supernova engine and nuclear equation of state. Here we use convolutional neural network models to identify the core rotational rates, rotation length scales, and the nuclear equation of state (EoS), using the 1824 waveforms from Richers et al. for a 12 solar mass progenitor. A high prediction accuracy for the classifications of the rotation length scales (93%) and the rotational rates (95%) can be achieved using the gravitational-wave signals from −10 to 6 ms core bounce. By including an additional 48 ms signal during the prompt convection phase, we could achieve an accuracy of 96% in the classification of the four main EoS groups. By combining the three models above, we could correctly predict the core rotational rates, rotation length scales, and the EoS at the same time with an accuracy of more than 85%. Finally, applying a transfer-learning method for an additional 74 waveforms from FLASH simulations, we show that our model using Richers’ waveforms could successfully predict the rotational rates from Pan’s waveforms even for a continuous value with mean absolute errors of 0.32 rad s−1 only. These results demonstrate the much broader parameter regimes to which our model can be applied to identify core-collapse supernova events through gravitational-wave signals.

Neutrino interactions in liquid scintillators including active-sterile neutrino mixing

Neutrinos play an important role in core-collapse supernova events since they are a key piece to understanding the explosion mechanisms. The analysis of the neutrino fluxes can bring answers to neutrino’s related problems e.g., mass hierarchy, spectral splitting, sterile neutrinos, etc. In this work, we study the impact of neutrino oscillations and the possible existence of eV sterile neutrinos upon the supernova neutrino flux ([Formula: see text]). We have calculated the energy distribution of the neutrino flux from a supernova and the total number of events that would be detected in a liquid scintillator. We also present an analysis for the conversion probabilities as a function of the active-sterile neutrino mixing parameters. Finally, we have carried out a statistical analysis to extract values for the mixing parameters of the model.

Binary neutron star merger in common envelope jets supernovae

ABSTRACT I explore a triple-star scenario where a tight neutron star (NS)–NS binary system enters the envelope of a red supergiant (RSG) star and spirals-in towards its core. The two NSs accrete mass through accretion discs and launch jets that power a very luminous and long transient event, a common envelope jets supernova (CEJSN) event. Dynamical friction brings the two NSs to merge either in the RSG envelope or core. The total energy of the event, radiation and kinetic, is $\gtrsim 10^{52} {~\rm erg}$. The light curve stays luminous for months to years and a signal of gravitational waves might be detected. The ejecta contain freshly synthesized r-process elements not only from the NS–NS merger as in kilonova events, but possibly also from the pre-merger jets that the NSs launch inside the core, as in the r-process CEJSN scenario. This scenario shortens the time to NS–NS merger compared with that of kilonovae, and might somewhat ease the problem of the NS–NS r-process scenario to account for r-process nucleosynthesis in the early Universe. I estimate the ratio of NS–NS merger in CEJSN events to core collapse supernova (CCSN) events to be ≲10−6 − 2 × 10−5. However, because they are much more luminous I expect their detection fraction to that of CCSNe to be much larger than this number. This study calls for considering this and similar CEJSN scenarios in binary and in triple-star systems when explaining peculiar and puzzling superluminous supernovae.

What can be learned from a proto-neutron star’s mass and radius?

ABSTRACT We make extensive numerical studies of masses and radii of proto-neutron stars during the first second after their birth in core-collapse supernova events. We use a quasi-static approach for the computation of proto-neutron star structure, built on parametrized entropy and electron fraction profiles, that are then evolved with neutrino cooling processes. We vary the equation of state of nuclear matter, the proto-neutron star mass, and the parameters of the initial profiles, to take into account our ignorance of the supernova progenitor properties. Our results suggest that if masses and radii of a proto-neutron star can be determined in the first second after the birth, e.g. from gravitational wave emission, no information could be obtained on the corresponding cold neutron star and therefore on the cold nuclear equation of state. Similarly, it seems unlikely that any property of the proto-neutron star equation of state (hot and not beta-equilibrated) could be determined either, mostly due to the lack of information on the entropy, or equivalently temperature, distribution in such objects.

‘Ears’ formation in supernova remnants: overhearing an interaction history with bipolar circumstellar structures

ABSTRACT A characteristic feature that is frequently found in nearby supernova remnants (SNRs) is the existence of two antisymmetric, local protrusions that are projected as two ‘ears’ in the morphology of the nebula. In this paper, we present a novel scenario for the ‘ear’ formation process, according to which the two lobes are formed through the interaction of the SNR with a bipolar circumstellar medium (CSM) that was surrounding the explosion’s centre. We conduct two-dimensional hydrodynamic simulations and we show that the SNR shock breakout from the bipolar CSM triggers the inflation of two opposite protrusions at the equator of the remnant, which retain their size and shape from several hundreds up to a few thousand years of the SNR evolution. We run a set of models by varying the supernova (SN) and CSM properties and we demonstrate that the extracted results reveal good agreement with the observables, regarding the sizes, lifespan, morphology and kinematics of the ‘ears’. We discuss the plausibility of our model in nature and we suggest that the most likely progenitors of the ‘ear-carrying’ SNRs are the luminous blue variables or the red/yellow supergiants for the SNRs resulting from core collapse SN events, and the symbiotic binaries or the planetary nebulae for the SNRs formed by Type Ia SNe. Finally, we compare our model with other ‘ear’ formation models found in the literature and we show that there are distinctive differences among them, concerning the orientation of the ‘ears’ and the phase in which the ‘ear’ formation process occurs.

On the rate of core collapse supernovae in the milky way

Several large neutrino telescopes, operating at various sites around the world, have as their main objective the first detection of neutrinos emitted by a gravitational collapse in the Milky Way. The success of these observation programs depends on the rate of supernova core collapse in the Milky Way, R. In this work, standard statistical techniques are used to combine several independent results. Their consistency is discussed and the most critical input data are identified. The inference on R is further tested and refined by including direct information on the occurrence rate of gravitational collapse events in the Milky Way and in the Local Group, obtained from neutrino telescopes and electromagnetic surveys. A conservative treatment of the errors yields a combined rate R=1.63±0.46 (100 yr)−1; the corresponding time between core collapse supernova events turns out to be T=61−14+24 yr. The importance to update the analysis of the stellar birthrate method is emphasized.

Constraining Properties of the Next Nearby Core-collapse Supernova with Multimessenger Signals

Abstract With the advent of modern neutrino and gravitational wave (GW) detectors, the promise of multimessenger detections of the next galactic core-collapse supernova (CCSN) has become very real. Such detections will give insight into the CCSN mechanism and the structure of the progenitor star, and may resolve longstanding questions in fundamental physics. In order to properly interpret these detections, a thorough understanding of the landscape of possible CCSN events, and their multimessenger signals, is needed. We present detailed predictions of neutrino and GW signals from 1D simulations of stellar core collapse, spanning the landscape of core-collapse progenitors from 9 to 120 M ⊙. In order to achieve explosions in 1D, we use the Supernova Turbulence In Reduced-dimensionality model, which includes the effects of turbulence and convection in 1D supernova simulations to mimic the 3D explosion mechanism. We study the GW emission from the 1D simulations using an astroseismology analysis of the protoneutron star. We find that the neutrino and GW signals are strongly correlated with the structure of the progenitor star and remnant compact object. Using these correlations, future detections of the first few seconds of neutrino and GW emission from a galactic CCSN may be able to provide constraints on stellar evolution independent of preexplosion imaging and the mass of the compact object remnant prior to fallback accretion.

44Ti ejecta in young supernova remnants

Context. Tracing unstable isotopes produced in supernova nucleosynthesis provides a direct diagnostic of supernova explosion physics. Theoretical models predict an extensive variety of scenarios, which can be constrained through observations of the abundant isotopes 56Ni and 44Ti. Direct evidence of the latter was previously found only in two core-collapse supernova events, and appears to be absent in thermonuclear supernovae. Aims. We aim to to constrain the supernova progenitor types of Cassiopeia A, SN 1987A, Vela Jr., G1.9+0.3, SN1572, and SN1604 through their 44Ti ejecta masses and explosion kinematics. Methods. We analyzed INTEGRAL/SPI observations of the candidate sources utilizing an empirically motivated high-precision background model. We analyzed the three dominant spectroscopically resolved de-excitation lines at 68, 78, and 1157 keV emitted in the decay chain of 44Ti→44Sc→44Ca. The fluxes allow the determination of the production yields of 44Ti. Remnant kinematics were obtained from the Doppler characteristics of the lines. Results. We find a significant signal for Cassiopeia A in all three lines with a combined significance of 5.4σ. The fluxes are (3.3 ± 0.9) × 10−5 ph cm−2 s−1, and (4.2 ± 1.0) × 10−5 ph cm−2 s−1 for the 44Ti and 44Sc decay, respectively. This corresponds to a mass of (2.4 ± 0.7) × 10−4 M⊙ and (3.1 ± 0.8) × 10−4 M⊙, respectively. We obtain higher fluxes for 44Ti with our analysis of Cassiopeia A than were obtained in previous analyses. We discuss potential differences. We interpret the line width from Doppler broadening as expansion velocity of (6400 ± 1900) km s−1. We do not find any significant signal for any other candidate sources. Conclusions. We obtain a high 44Ti ejecta mass for Cassiopeia A that is in disagreement with ejecta yields from symmetric 2D models. Upper limits for the other core-collapse supernovae are in agreement with model predictions and previous studies. The upper limits we find for the three thermonuclear supernovae (G1.9+0.3, SN1572 and SN1604) consistently exclude the double detonation and pure helium deflagration models as progenitors.

The explosive life of massive binaries

Massive stars are born predominantly as members of binary (or higher multiplicity) systems, and the presence of a companion can significantly alter their life and final fate. Therefore, any observed sample of massive stars or associated transients is likely to be significantly influenced by the effects of binarity. Here, we focus on the relationship between massive binary evolution and core-collapse supernova events. In the vast majority of the cases, the first core-collapse event happening in a binary system unbinds the two stars. Studying the population of companion stars, either at the supernova site, or as "widowed" stars long after the explosion, can be used to constrain the previous orbital evolution of the binary progenitor, and explosion physics of their former companion. Specifically, the population of "widowed" stars might provide statistical constraints on the typical amplitude of black hole natal kicks without seeing neither the black holes nor the transient possibly associated with their formation. Binarity also has a large impact on the predicted population of supernova sub-types, including hydrogen-rich type II supernovae, with a significant fraction of hydrogen-rich stars at explosions being either merger products or accretors.

Spectrophotometric templates for core-collapse supernovae and their application in simulations of time-domain surveys

ABSTRACT The design and analysis of time-domain sky surveys require the ability to simulate accurately realistic populations of core-collapse supernova (SN) events. We present a set of spectral time-series templates designed for this purpose, for both hydrogen-rich (Type II, IIn, and IIb) and stripped-envelope (Type Ib, Ic, and Ic-BL) core-collapse SNe. We use photometric and spectroscopic data for 67 core-collapse SNe from the literature, and for each generate a time-series spectral template. The techniques used to build the templates are fully data driven with no assumption of any parametric form or model for the light curves. The template-building code is open source, and can be applied to any transient for which well-sampled multiband photometry and multiple spectroscopic observations are available. We extend these spectral templates into the near-ultraviolet to λ ≃ 1600 Å using observer-frame ultraviolet photometry. We also provide a set of templates corrected for host galaxy dust extinction, and provide a set of luminosity functions that can be used with our spectral templates in simulations. We give an example of how these templates can be used by integrating them within the popular SN simulation package snana, and simulating core-collapse SNe in photometrically selected cosmological Type Ia SN samples, prone to contamination from core-collapse events.

TRACKING THE DISTRIBUTION OF 26Al AND 60Fe DURING THE EARLY PHASES OF STAR AND DISK EVOLUTION

ABSTRACT The short-lived 26Al and 60Fe radionuclides are synthesized and expelled into the interstellar medium by core-collapse supernova events. The solar system’s first solids, calcium–aluminum refractory inclusions (CAIs), contain evidence for the former presence of the 26 Al nuclide defining the canonical 26Al/27 Al ratio of . A different class of objects temporally related to canonical CAIs are CAIs with fractionation and unidentified nuclear effects (FUN CAIs), which record a low initial 26Al/27Al of 10−6. The contrasting level of 26Al between these objects is often interpreted as reflecting the admixing of the 26Al nuclides during the early formative phase of the Sun. We use giant molecular cloud scale adaptive mesh-refinement numerical simulations to trace the abundance of 26Al and 60Fe in star-forming gas during the early stages of accretion of individual low-mass protostars. We find that the 26Al/27Al and 60Fe/56Fe ratios of accreting gas within a vicinity of 1000 au of the stars follow the predicted decay curves of the initial abundances at the time of star formation without evidence of spatial or temporal heterogeneities for the first 100 kyr of star formation. Therefore, the observed differences in 26Al/27Al ratios between FUN and canonical CAIs are likely not caused by admixing of supernova material during the early evolution of the proto-Sun. Selective thermal processing of dust grains is a more viable scenario to account for the heterogeneity in 26Al/27Al ratios at the time of solar system formation.

Near Real-time Data Analysis of Core-collapse Supernova Simulations with Bellerophon

We present an overview of a software system, Bellerophon, built to support a production-level HPC application called CHIMERA, which simulates core-collapse supernova events at the petascale. Developed over the last four years, Bellerophon enables CHIMERA's geographically dispersed team of collaborators to perform data analysis in near real-time. Its n-tier architecture provides an encapsulated, end-to-end software solution that enables the CHIMERA team to quickly and easily access highly customizable animated and static views of results from anywhere in the world via a web- deliverable, cross-platform desktop application. In addition, Bellerophon addresses software engineering tasks for the CHIMERA team by providing an automated mechanism for performing regression testing on a variety of supercomputing platforms. Elements of the team's workflow management needs are met with software tools that dynamically generate code repository statistics, access important online resources, and monitor the current status of several supercomputing resources.

Detection of a Noble Gas Molecular Ion, 36 ArH + , in the Crab Nebula

Noble gas molecules have not hitherto been detected in space. From spectra obtained with the Herschel Space Observatory, we report the detection of emission in the 617.5- and 1234.6-gigahertz J = 1-0 and 2-1 rotational lines of (36)ArH(+) at several positions in the Crab Nebula, a supernova remnant known to contain both molecular hydrogen and regions of enhanced ionized argon emission. Argon-36 is believed to have originated from explosive nucleosynthesis in massive stars during core-collapse supernova events. Its detection in the Crab Nebula, the product of such a supernova event, confirms this expectation. The likely excitation mechanism for the observed (36)ArH(+) emission lines is electron collisions in partially ionized regions with electron densities of a few hundred per centimeter cubed.

RADIATION-HYDRODYNAMICAL MODELING OF CORE-COLLAPSE SUPERNOVAE: LIGHT CURVES AND THE EVOLUTION OF PHOTOSPHERIC VELOCITY AND TEMPERATURE

We have developed a relativistic, radiation-hydrodynamics Lagrangian code, specifically tailored to simulate the evolution of the main observables (light curve and the evolution of photospheric velocity and temperature) in core-collapse supernova (CC-SN) events. The distinctive features of the code are an accurate treatment of radiative transfer coupled to relativistic hydrodynamics, a self-consistent treatment of the evolution of the innermost ejecta taking into account the gravitational effects of the central compact remnant, and a fully implicit Lagrangian approach to the solution of the coupled nonlinear finite difference system of equations. Our aim is to use it as a numerical tool to perform calculations of a grid of models to be compared with observations of CC-SNe. In this paper, we present some testcase simulations and a comparison with observations of SN 1987A, as well as with the results obtained with other numerical codes. We also briefly discuss the influence of the main physical parameters (ejected mass, progenitor radius, explosion energy, amount of 56Ni) on the evolution of the ejecta, and the implications of our results in connection with the possibility to "standardize" hydrogen-rich CC-SNe for using them as candles to measure cosmological distances.

What are the astrophysical sites for the [formula omitted]-process and the production of heavy elements?

This article addresses three of the four nucleosynthesis processes involved in producing heavy nuclei beyond Fe (with a main focus on the r -process). Opposite to the fourth process (the s -process), which operates in stellar evolution during He- and C-burning, they are all related to explosive burning phases, (presumably) linked to core collapse supernova events of massive stars. The (classical) p -process is identified with explosive Ne/O-burning in outer zones of the progenitor star. It is initiated by the passage of the supernova shock wave and acts via photodisintegration reactions like a spallation process which produces neighboring (proton-rich) isotopes from pre-existing heavy nuclei. The reproduction of some of the so-called lighter p -isotopes with A < 100 faces problems in this environment. The only recently discovered ν p -process is related to the innermost ejecta, the neutrino wind expelled from the hot proto-neutron star after core collapse and the supernova explosion. This neutrino wind is proton-rich in its early phase, producing nuclei up to 64Ge. Reactions with neutrinos permit to overcome decay/reaction bottlenecks for the flow beyond 64Ge, thus producing light p -isotopes, which face problems in the classical p -process scenario. The understanding of the r -process, being identified for a long time with rapid neutron captures and passing through nuclei far from stability, is still experiencing major problems. These are on the one hand related to nuclear uncertainties far from stability (masses, half-lives, fission barriers), affecting the process speed and abundance peaks. On the other hand the site is still not definitely located, yet. (i) Later, possibly neutron-rich, high entropy phases of the neutrino wind (if they materialize!) could permit its operation. (ii) Other options include the ejection of very neutron-rich neutron star-like matter, occurring possibly in neutron star mergers or core collapse supernova events with jets, related to prior stellar evolution with high rotation rates and magnetic fields. Two different environments are required for a weak and a main/strong r -process, witnessed by observations of low metallicity stars and meteoritic inclusions, which could possibly be identified with the two options listed above, i.e. the weak r -process could be related to the neutrino wind when changing from p -rich to n -rich conditions.

The r-, p-, and νp-Process

The processes discussed in this review are three of the four nucleosynthesis processes involved in producing heavy nuclei beyond Fe (not counting the rp-process in X-ray bursts). Opposite to the fourth process (the s-process), which operates in stellar evolution during He- and C-burning, they are all related to explosive burning phases, (presumably) linked to core collapse supernova events of massive stars. The (classical) p-process is identified with explosive Ne/O-burning in outer zones of the progenitor star. It is intitiated by the passage of the supernova shock wave and acts via photodisintegration reactions like a spallation process which produces neighboring (proton-rich) isotopes from pre-existing heavy nuclei. The reproduction of some of the so-called lighter p-isotopes with A < 100 faces problems in this environment. The only recently discovered νp-process is related to the innermost ejecta, the neutrino wind expelled from the hot proto-neutron star after core collapse in the supernova explosion. This neutrino wind is proton-rich in its early phase and reactions with neutrinos permit to overcome decay/reaction bottlenecks for the flow beyond the Fe-group, thus permitting the production of those p-isotopes, which face problems in the classical p-process scenario. The understanding of the r-process, being identified for a long time with rapid neutron captures – and passing through nuclei far from stability – is still experiencing major problems. These are on the one hand related to nuclear uncertainties far from stability (masses and half-lives), affecting the process speed and abundance peaks, on the other hand the site is still not definitely located, yet. Later neutron-rich, high entropy phases of the neutrino wind could permit its operation, other options include the ejection of very neutron-rich neutron star matter. Two different environments are required for a weak and a main/strong r-process, witnessed by observations of low metallicity stars.