Keywords

SNe Ia continue to play a key role in cosmological measurements. Their interpretation over a range in redshift requires a rest-frame spectral energy distribution model. For practicality, these models are parameterized with a limited number of parameters and are trained using linear or nonlinear dimensionality reduction. This work focuses on the related problem of estimating the number of parameters underlying SN Ia spectral variation (the dimensionality). I present a technique for using the properties of high-dimensional space and the counting statistics of "twin" SNe Ia to estimate this dimensionality. Applying this method to the supernova pairings from Fakhouri et al. shows that a modest number of parameters (three to five, not including extinction) explain those data well. The analysis also finds that the intrinsic parameters are approximately Gaussian-distributed. The limited number of parameters hints that improved SED models are possible that may enable substantial reductions in SN cosmological uncertainties with current and near-term data sets.

Unlike ordinary supernovae (SNe), some of which are hydrogen and helium deficient (called Type Ic SNe), broad-lined Type Ic SNe (SNe Ic-bl) are very energetic events, and only SNe Ic-bl are coincident with long-duration gamma-ray bursts (GRBs). Understanding the progenitors of SN Ic-bl explosions versus those of their SN Ic cousins is key to understanding the SN–GRB relationship and jet production in massive stars. Here we present the largest existing set of host galaxy spectra of 28 SNe Ic and 14 SNe Ic-bl, all discovered by the same galaxy-untargeted survey, namely, the Palomar Transient Factory (PTF). We carefully measure their gas-phase metallicities, stellar masses (M_*), and star formation rates (SFRs). We further reanalyze the hosts of 10 literature SN–GRBs using the same methods and compare them to our PTF SN hosts with the goal of constraining their progenitors from their local environments. We find that the metallicities, SFRs, and M_* values of our PTF SN Ic-bl hosts are statistically comparable to those of SN–GRBs but significantly lower than those of the PTF SNe Ic. The mass–metallicity relations as defined by the SNe Ic-bl and SN–GRBs are not significantly different from the same relations as defined by Sloan Digital Sky Survey galaxies, contradicting claims by earlier works. Our findings point toward low metallicity as a crucial ingredient for SN Ic-bl and SN–GRB production since we are able to break the degeneracy between high SFR and low metallicity. We suggest that the PTF SNe Ic-bl may have produced jets that were choked inside the star or were able to break out of the star as unseen low-luminosity or off-axis GRBs.

We present a carefully designed, systematic study of the angular resolution dependence of simulations with the Prometheus-Vertex neutrino-hydrodynamics code. Employing a simplified neutrino heating–cooling scheme in the Prometheus hydrodynamics module allows us to sample the angular resolution between 4° and 05. With a newly implemented static mesh refinement (SMR) technique on the Yin-Yang grid, the angular coordinates can be refined in concentric shells, compensating for the diverging structure of the spherical grid. In contrast to previous studies with Prometheus and other codes, we find that higher angular resolution and therefore lower numerical viscosity provides more favorable explosion conditions and faster shock expansion. We discuss the possible reasons for the discrepant results. The overall dynamics seem to converge at a resolution of about 1°. Applying the SMR setup to marginally exploding progenitors is disadvantageous for the shock expansion, however, because the kinetic energy of downflows is dissipated to internal energy at resolution interfaces, leading to a loss of turbulent pressure support and a steeper temperature gradient. We also present a way to estimate the numerical viscosity on grounds of the measured turbulent kinetic energy spectrum, leading to smaller values that are better compatible with the flow behavior witnessed in our simulations than results following calculations in previous literature. Interestingly, the numerical Reynolds numbers in the turbulent, neutrino-heated postshock layer (some 10 to several hundred) are in the ballpark of expected neutrino drag effects on the relevant length scales. We provide a formal derivation and quantitative assessment of the neutrino drag terms in an appendix.

Most one-dimensional core-collapse simulations fail to explode, yet multidimensional simulations often explode. A dominant multidimensional effect aiding explosion is neutrino-driven convection. We incorporate a convection model in approximate one-dimensional core-collapse supernova (CCSN) simulations. This is the 1D+ method. This convection model lowers the neutrino luminosity required for explosion by $\sim 30$%, similar to the reduction observed in multidimensional simulations. The model is based upon the global turbulence model of Mabanta & Murphy and models the mean-field turbulent flow of neutrino-driven convection. In this preliminary investigation, we use simple neutrino heating and cooling algorithms to compare the critical condition in the 1D+ simulations with the critical condition observed in two-dimensional simulations. Qualitatively, the critical conditions in the 1D+ and the two-dimensional simulations are similar. The assumptions in the convection model affect the radial profiles of density, entropy, and temperature, and comparisons with the profiles of three-dimensional simulations will help to calibrate these assumptions. These 1D+ simulations are consistent with the profiles and explosion conditions of equivalent two-dimensional CCSN simulations but are ∼10² times faster, and the 1D+ prescription has the potential to be ∼10⁵ faster than three-dimensional CCSN simulations. With further calibration, the 1D+ technique could be ideally suited to test the explodability of thousands of progenitor models.

We propose that the inner engine of a type I binary-driven hypernova (BdHN) is composed of Kerr black hole (BH) in a non-stationary state, embedded in a uniform magnetic field B₀ aligned with the BH rotation axis and surrounded by an ionized plasma of extremely low density of 10⁻¹⁴ g cm⁻³. Using GRB 130427A as a prototype, we show that this inner engine acts in a sequence of elementary impulses. Electrons accelerate to ultrarelativistic energy near the BH horizon, propagating along the polar axis, θ = 0, where they can reach energies of ∼10¹⁸ eV, partially contributing to ultrahigh-energy cosmic rays. When propagating with $\theta \ne 0$ through the magnetic field B₀, they produce GeV and TeV radiation through synchroton emission. The mass of BH, M = 2.31M_⊙, its spin, α = 0.47, and the value of magnetic field B₀ = 3.48 × 10¹⁰ G, are determined self consistently to fulfill the energetic and the transparency requirement. The repetition time of each elementary impulse of energy ${ \mathcal E }\sim {10}^{37}$ erg is ∼10⁻¹⁴ s at the beginning of the process, then slowly increases with time evolution. In principle, this "inner engine" can operate in a gamma-ray burst (GRB) for thousands of years. By scaling the BH mass and the magnetic field, the same inner engine can describe active galactic nuclei.

We present a systematic study of the most luminous (M_IR [Vega magnitudes] brighter than −14) infrared (IR) transients discovered by the SPitzer InfraRed Intensive Transients Survey (SPIRITS) between 2014 and 2018 in nearby galaxies (D < 35 Mpc). The sample consists of nine events that span peak IR luminosities of M_[4.5],peak between −14 and −18.2, show IR colors between 0.2 < ([3.6]–[4.5]) < 3.0, and fade on timescales between 55 days < t_fade < 480 days. The two reddest events (A_V > 12) show multiple, luminous IR outbursts over several years and have directly detected, massive progenitors in archival imaging. With analyses of extensive, multiwavelength follow-up, we suggest the following possible classifications: five obscured core-collapse supernovae (CCSNe), two erupting massive stars, one luminous red nova, and one intermediate-luminosity red transient. We define a control sample of all optically discovered transients recovered in SPIRITS galaxies and satisfying the same selection criteria. The control sample consists of eight CCSNe and one Type Iax SN. We find that 7 of the 13 CCSNe in the SPIRITS sample have lower bounds on their extinction of 2 < A_V < 8. We estimate a nominal fraction of CCSNe in nearby galaxies that are missed by optical surveys as high as ${38.5}_{-21.9}^{+26.0} \%$ (90% confidence). This study suggests that a significant fraction of CCSNe may be heavily obscured by dust and therefore undercounted in the census of nearby CCSNe from optical searches.

Type IIb supernovae (SNe) are important candidates to understand mechanisms that drive the stripping of stripped-envelope (SE) supernova (SN) progenitors. While binary interactions and their high incidence are generally cited to favor them as SN IIb progenitors, this idea has not been tested using models covering a broad parameter space. In this paper, we use non-rotating single- and binary-star models at solar and low metallicities spanning a wide parameter space in primary mass, mass ratio, orbital period, and mass transfer efficiencies. We find that our single- and binary-star models contribute to roughly equal, however small, numbers of SNe IIb at solar metallicity. Binaries only dominate as progenitors at low metallicity. We also find that our models can account for less than half of the observationally inferred rate for SNe IIb at solar metallicity, with computed rates ≲4% of core-collapse (CC) SNe. On the other hand, our models can account for the rates currently indicated by observations at low metallicity, with computed rates as high as 15% of CC SNe. However, this requires low mass transfer efficiencies (≲0.1) to prevent most progenitors from entering contact. We suggest that the stellar wind mass-loss rates at solar metallicity used in our models are too high. Lower mass-loss rates would widen the parameter space for binary SNe IIb at solar metallicity by allowing stars that initiate mass transfer earlier in their evolution to reach CC without getting fully stripped.

We have studied double-detonation explosions in double-degenerate (DD) systems with different companion white dwarfs (WDs) for modeling Type Ia supernovae (SNe Ia) by means of high-resolution smoothed particle hydrodynamics (SPH) simulations. We have found that only the primary WDs explode in some of the DD systems, while the explosions of the primary WDs induce the explosions of the companion WDs in the other DD systems. The former case is a so-called dynamically-driven double-degenerate double-detonation (D⁶) explosion, or helium-ignited violent merger explosion. The SN ejecta of the primary WDs strip materials from the companion WDs, whose mass is ∼10⁻³ M_⊙. The stripped materials contain carbon and oxygen when the companion WDs are carbon–oxygen (CO) WDs with He shells ≲0.04 M_⊙. Since they contribute to low-velocity ejecta components as observationally inferred for iPTF14atg, D⁶ explosions can be counterparts of subluminous SNe Ia. The stripped materials may contribute to low-velocity C seen in several SNe Ia. In the latter case, the companion WDs explode through He detonation if they are He WDs and through the double-detonation mechanism if they are CO WDs with He shells. We name these explosions "triple" and "quadruple" detonation (TD/QD) explosions after the number of detonations. The QD explosion may be counterparts of luminous SNe Ia, such as SN 1991T and SN 1999aa, since they yield a large amount of ⁵⁶Ni, and their He-detonation products contribute to the early emissions accompanying such luminous SNe Ia. On the other hand, the TD explosion may not yield a sufficient amount of ⁵⁶Ni to explain luminous SNe Ia.

We present DASH (Deep Automated Supernova and Host classifier), a novel software package that automates the classification of the type, age, redshift, and host galaxy of supernova spectra. DASH makes use of a new approach that does not rely on iterative template-matching techniques like all previous software, but instead classifies based on the learned features of each supernova's type and age. It has achieved this by employing a deep convolutional neural network to train a matching algorithm. This approach has enabled DASH to be orders of magnitude faster than previous tools, being able to accurately classify hundreds or thousands of objects within seconds. We have tested its performance on 4 yr of data from the Australian Dark Energy Survey (OzDES). The deep learning models were developed using TensorFlow and were trained using over 4000 supernova spectra taken from the CfA Supernova Program and the Berkeley SN Ia Program as used in SNID (Supernova Identification software). Unlike template-matching methods, the trained models are independent of the number of spectra in the training data, which allows for DASH's unprecedented speed. We have developed both a graphical interface for easy visual classification and analysis of supernovae and a Python library for the autonomous and quick classification of several supernova spectra. The speed, accuracy, user-friendliness, and versatility of DASH present an advancement to existing spectral classification tools. We have made the code publicly available on GitHub and PyPI (pip install astrodash) to allow for further contributions and development. The package documentation is available at https://astrodash.readthedocs.io.

Recent high-cadence transient surveys and rapid follow-up observations indicate that some massive stars may dynamically lose their own mass within decades before supernovae (SNe). Such a mass-loss forms "confined" circumstellar medium (CSM); a high-density material distributed only within a small radius (≲10¹⁵ cm with the mass-loss rate of 0.01 ∼ 10⁻⁴ M_⊙ yr⁻¹). While the SN shock should trigger particle acceleration and magnetic field amplification in the "confined" CSM, synchrotron emission may be masked in centimeter wavelengths due to free–free absorption; the millimeter range can, however, be a potential new window. We investigate the time evolution of synchrotron radiation from the system of a red supergiant surrounded by the "confined" CSM, relevant to typical Type II-P SNe. We show that synchrotron millimeter emission is generally detectable, and that the signal can be used as a sensitive tracer of the nature of the "confined" CSM; it traces different CSM density parameter space than in the optical. Furthermore, our simulations show that the "confined" CSM efficiently produces secondary electrons and positrons through proton inelastic collisions, which can become main contributors to the synchrotron emission in several ten days since the SN. We predict that the synchrotron emission is detectable by ALMA, and suggest that it will provide a robust evidence of the existence of the "confined" CSM.