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In this paper, we calculate the energy, signal-to-noise ratio (SNR), detection range, and angular anisotropy of the matter, matter memory, and neutrino memory gravitational-wave (GW) signatures of 21 three-dimensional initially nonrotating core-collapse supernova (CCSN) models carried to late times. We find that inferred energy, SNR, and detection range are angle-dependent quantities, and that the spread of possible energy, signal to noise, and detection ranges across all viewing angles generally increases with progenitor mass. When examining the low-frequency matter memory and neutrino memory components of the signal, we find that the neutrino memory is the most detectable component of a CCSN GW signal, and that DECIGO is best equipped to detect both matter memory and neutrino memory. Moreover, we find that the polarization angle between the h + and h × strains serves as a unique identifier of matter and neutrino memory. Finally, we develop a Galactic density- and stellar mass-weighted formalism to calculate the rate at which we can expect to detect CCSN GW signals with the Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO). When considering only the matter component of the signal, the aLIGO detection rate is around 65% of the total Galactic supernova rate, but increases to 90% when incorporating the neutrino memory component. We find that all future detectors (Einstein Telescope, Cosmic Explorer, DECIGO) will be able to detect CCSN GW signals from the entire Galaxy, and for the higher-mass progenitors even into the Local Group of galaxies. [ABSTRACT FROM AUTHOR]

The elemental abundances of stars reflect the complex enrichment history of the Galaxy. To explore and explain the metal enrichment history of the cosmic environment near our solar system, we study the evolution of 56Fe abundance over time and [Mg/Fe] versus [Fe/H] evolution in the solar neighborhood. Core-collapse supernovae make the dominant contribution in the early stages, while Type Ia supernovae (SNe Ia) have a delayed and dominant impact in the later stages. In this work, we consider the nucleosynthesis contribution of neutrino-dominated accretion flows (NDAFs) formed at the end of the lives of massive stars. The results show that the [Fe/H] gradually increases over time and eventually reaches [Fe/H] = 0 and above, reproducing the chemical enrichment process in the solar neighborhood. Before the onset of SNe Ia, the ratio of 56Fe mass to the total gas mass increases by a factor of at most ∼1.44 when NDAFs are taken into account. We find that by including NDAF in our models, the agreement with the observed metallicity distribution of metal-poor stars in the solar neighborhood (<1 kpc) is improved while not significantly altering the location of the metallicity peak. This inclusion can also reproduce the observed evolutionary change of [Mg/Fe] at [Fe/H] ∼ −1.22, bringing the ratio to match the solar abundance. Our results provide an extensive understanding of metallicity evolution in solar environments by highlighting the nucleosynthesis contribution of NDAF outflows in the solar neighborhood. [ABSTRACT FROM AUTHOR]

It is well known that gravitational waves (GWs) undergo no absorption or dissipation when traversing through a perfect fluid. However, in the presence of a viscous fluid, GWs transfer energy to the fluid medium. In this paper, we present a review of our recent series of results regarding the interaction between GWs and surrounding matter. Additionally, we examine the impact of a viscous fluid shell on GW propagation, focusing particularly on GW damping and GW heating. Furthermore, we explore the significance of these effects in various astrophysical scenarios such as core-collapse supernovae and primordial GWs. [ABSTRACT FROM AUTHOR]

The interaction of supernova ejecta with a surrounding circumstellar medium (CSM) generates a strong shock, which can convert ejecta kinetic energy into observable radiation. Given the diversity of potential CSM structures (arising from diverse mass-loss processes such as late-stage stellar outbursts, binary interaction, and winds), the resulting transients can display a wide range of light-curve morphologies. We provide a framework for classifying the transients arising from interaction with a spherical CSM shell. The light curves are decomposed into five consecutive phases, starting from the onset of interaction and extending through shock breakout and subsequent shock cooling. The relative prominence of each phase in the light curve is determined by two dimensionless quantities representing the CSM-to-ejecta mass ratio η, and the breakout parameter ξ. These two parameters define four light-curve morphology classes, where each class is characterized by the location of the shock breakout and the degree of deceleration as the shock sweeps up the CSM. We compile analytic scaling relations connecting the luminosity and duration of each light-curve phase to the physical parameters. We then run a grid of radiation hydrodynamics simulations for a wide range of ejecta and CSM parameters to numerically explore the landscape of interaction light curves, and to calibrate and confirm the analytic scalings. We connect our theoretical framework to several case studies of observed transients, highlighting the relevance in explaining slow-rising and superluminous supernovae, fast blue optical transients, and double-peaked light curves. [ABSTRACT FROM AUTHOR]

It is generally hard to put robust constraints on progenitor masses of supernovae and supernova remnants (SNRs) observationally, while they offer tantalizing clues to understanding explosion mechanisms and mass distribution. Our recent study suggests that "shell merger," which is theoretically expected for stellar evolution, can appreciably affect the final yields of intermediate-mass elements (IMEs; such as Ne, Mg, and Si). In light of this, here we report the results of the X-ray spectral analysis of a Galactic SNR G359.0−0.9, whose abundance pattern may possibly be anomalous according to a previous study. Our spectroscopy using all the available data taken with XMM-Newton reveals that this remnant is classified as a Mg-rich SNR because of its high Mg-to-Ne ratio ( Z Mg / Z Ne = 1.90 − 0.19 + 0.27 ; mass ratio 0.66 − 0.07 + 0.09 ) and conclude that the result cannot be explained without the shell merger. By comparing the observation with theoretical calculations, we prefer the so-called Ne-burning shell intrusion and in this case, the progenitor mass M ZAMS is likely <15 M ⊙. We confirm the result also with our new molecular-line observations with the Nobeyama 45 m telescope: G359.0−0.9 is located in the Scutum–Centaurus arm (2.66–2.94 kpc) and in this case, the resultant total ejecta mass ∼6.8 M ⊙ is indeed consistent with the above estimate. Our method using mass ratios of IMEs presented in this paper will become useful to distinguish the type of shell merger, the Ne-burning shell intrusion, and the O-burning shell merger, for future SNR studies. [ABSTRACT FROM AUTHOR]

We here focus on the behavior of supernovae that technically explode in 1D (spherical symmetry). When simulated in 3D, however, the outcomes of representative progenitors of this class are quite different in almost all relevant quantities. In 3D, the explosion energies can be 2 to 10 times higher, and there are correspondingly large differences in the 56Ni yields. These differences between the 3D and 1D simulations reflect in part the relative delay to explosion of the latter and in the former the presence of protoneutron star convection that boosts the driving neutrino luminosities by as much as ∼50% at later times. In addition, we find that the ejecta in 3D models are more neutron-rich, resulting in significant weak r -process and 48Ca yields. Furthermore, we find that in 3D the core is an interesting, though subdominant, source of acoustic power. In summary, we find that though a model might be found theoretically to explode in 1D, one must perform supernova simulations in 3D to capture most of the associated observables. The differences between 1D and 3D models are just too large to ignore. [ABSTRACT FROM AUTHOR]

The enrichment history of r -process elements has been imprinted on the stellar abundances that change in accordance with increasing metallicity in galaxies. Close examination of the [Eu/Fe] feature caused by stars in nearby galaxies, including the Large Magellanic Cloud (LMC), shows its perplexity. The decreasing trend of the [Eu/Fe] feature is followed by a nearly constant value; this trend is generally attributed to an onset of the delayed Fe release from Type Ia supernovae (SNe Ia), which is the same interpretation of the [ α /Fe] feature. However, this feature appears in the LMC at [Fe/H] of approximately −0.7, which is significantly higher than that for the [ α /Fe] case (≈−2). This result potentially indicates the presence of an overlooked property of the r -process site that remains unseen in the study of the Milky Way. Here, we propose that this [Eu/Fe]-knee feature is created by a fade-out of core-collapse SNe producing r -process elements; these elements along with neutron star mergers (NSMs) promote the r -process enrichment under the condition for this specific SNe such that their occurrence is limited to a low-metallicity environment. This metallicity threshold for the occurrence rate of r -process SNe at a subsolar is nearly identical to that for long gamma-ray bursts whose origin may be connected to fast-rotating massive stars. Moreover, we reason that the contribution of Eu from NSMs is crucial to maintain a high [Eu/Fe] at an early stage in dwarf galaxies by a balance with Fe from SNe Ia; both enrichments via NSMs and SNe Ia proceed with similar delay time distributions. [ABSTRACT FROM AUTHOR]

Based on our Chandra imaging-spectroscopic observations, we present the latest evolution of the X-ray remnant of SN 1987A. Recent changes in the electron temperatures and volume emission measures suggest that the blast wave in SN 1987A is moving out of the dense inner ring structure, also called the equatorial ring (ER). The 0.5–2.0 keV X-ray light curve shows a linearly declining trend (by ∼4.5% yr−1) between 2016 and 2020 as the blast wave heats the hitherto unknown circumstellar medium (CSM) outside the ER. While the peak X-ray emission in the latest 0.3–8.0 keV image is still within the ER, the radial expansion rate in the 3.0–8.0 keV images suggests an increasing contribution of the X-ray emission from less dense CSM since 2012, at least partly from beyond the ER. It is remarkable that, since 2020, the declining soft X-ray flux has stabilized around ∼7 × 10−12 erg s−1 cm−2, which may signal a contribution from the reverse-shocked outer layers of ejecta as predicted by the three-dimensional magnetohydrodynamic models. In the latest ACIS spectrum of supernova remnant 1987A in 2022 we report a significant detection of the Fe K line at ∼6.7 keV, which may be due to changing thermal conditions of the X-ray emitting CSM and/or the onset of reverse shock interactions with the Fe ejecta. [ABSTRACT FROM AUTHOR]

The elemental abundances between strontium and silver (Z = 38–47) observed in the atmospheres of very metal-poor stars in the Galaxy may contain the fingerprint of the weak r -process and ν p -process occurring in early core-collapse supernovae explosions. In this work, we combine various astrophysical conditions based on a steady-state model to cover the richness of the supernova ejecta in terms of entropy, expansion timescale, and electron fraction. The calculated abundances based on different combinations of conditions are compared with stellar observations, with the aim of constraining supernova ejecta conditions. We find that some conditions of the neutrino-driven outflows consistently reproduce the observed abundances of our sample. In addition, from the successful combinations, the neutron-rich trajectories better reproduce the observed abundances of Sr–Zr (Z = 38–40), while the proton-rich ones, Mo–Pd (Z = 42–47). [ABSTRACT FROM AUTHOR]

The detailed structure of core-collapse supernova progenitors is crucial for studying supernova explosion engines and the corresponding multimessenger signals. In this paper, we investigate the influence of stellar rotation on binary systems consisting of a 30 M ⊙ donor star and a 20 M ⊙ accretor using the MESA stellar evolution code. We find that through mass transfer in binary systems, fast-rotating red- and blue-supergiant progenitors can be formed within a certain range of the initial orbital periods, although the correlation is not linear. We also find that even with the same initial mass ratio of the binary system, the resulting final masses of the collapsars, the iron core masses, the compactness parameters, and the final rotational rates can vary widely and are sensitive to the initial orbital periods. For instance, the progenitors with strong convection form a thinner Si shell and a wider O shell compared to those in single-star systems. In addition, we conduct 2D self-consistent core-collapse supernova simulations with neutrino transport for these rotating progenitors derived from binary stellar evolution. We find that the neutrino and gravitational-wave signatures of these binary progenitors could exhibit significant variations. Progenitors with larger compactness parameters produce more massive proto-neutron stars, have higher mass accretion rates, and emit brighter neutrino luminosity and louder gravitational emissions. Finally, we observe stellar-mass black hole formation in some of our failed exploding models. [ABSTRACT FROM AUTHOR]

Most massive stars end their lives with core collapse. However, it is not clear which explode as a core-collapse supernova (CCSN), leaving behind a neutron star, and which collapse to a black hole, aborting the explosion. One path to predict explodability without expensive multidimensional simulations is to develop analytic explosion conditions. These analytic conditions also provide a deeper understanding of the explosion mechanism and they provide some insight into why some simulations explode and some do not. The analytic force explosion condition (FEC) reproduces the explosion conditions of spherically symmetric CCSN simulations. In this follow-up manuscript, we include the dominant multidimensional effect that aids explosion—neutrino-driven convection—in the FEC. This generalized critical condition (FEC+) is suitable for multidimensional simulations and has potential to accurately predict explosion conditions of two- and three-dimensional CCSN simulations. We show that adding neutrino-driven convection reduces the critical condition by ∼30%, which is consistent with previous multidimensional simulations. [ABSTRACT FROM AUTHOR]

We present the discovery and analysis of SN 2022oqm, a Type Ic supernova (SN) detected <1 day after the explosion. The SN rises to a blue and short-lived (2 days) initial peak. Early-time spectral observations of SN 2022oqm show a hot (40,000 K) continuum with high ionization C and O absorption features at velocities of 4000 km s−1, while its photospheric radius expands at 20,000 km s−1, indicating a pre-existing distribution of expanding C/O material. After ∼2.5 days, both the spectrum and light curves evolve into those of a typical SN Ic, with line velocities of ∼10,000 km s−1, in agreement with the evolution of the photospheric radius. The optical light curves reach a second peak at t ≈ 15 days. By t = 60 days, the spectrum of SN 2022oqm becomes nearly nebular, displaying strong Ca ii and [Ca ii ] emission with no detectable [O i ], marking this event as Ca-rich. The early behavior can be explained by 10−3 M ⊙ of optically thin circumstellar material (CSM) surrounding either (1) a massive compact progenitor such as a Wolf–Rayet star, (2) a massive stripped progenitor with an extended envelope, or (3) a binary system with a white dwarf. We propose that the early-time light curve is powered by both the interaction of the ejecta with the optically thin CSM and shock cooling (in the massive star scenario). The observations can be explained by CSM that is optically thick to X-ray photons, is optically thick in the lines as seen in the spectra, and is optically thin to visible-light continuum photons that come either from downscattered X-rays or from the shock-heated ejecta. Calculations show that this scenario is self-consistent. [ABSTRACT FROM AUTHOR]

Observations and theory suggest that core-collapse supernovae can span a range of explosion energies, and when sub-energetic the shockwave initiating the explosion can decelerate to speeds comparable to the escape speed of the progenitor. In these cases, gravity will complicate the explosion hydrodynamics and conceivably cause the shock to stall at large radii within the progenitor star. To understand these unique properties of weak explosions, we develop a perturbative approach for modeling the propagation of an initially strong shock into a time-steady, infalling medium in the gravitational field of a compact object. This method writes the shock position and the post-shock velocity, density, and pressure as series solutions in the (time-dependent) ratio of the freefall speed to the shock speed, and predicts that the shock stalls within the progenitor if the explosion energy is below a critical value. We show that our model agrees very well with hydrodynamic simulations, and accurately predicts (for example) the time-dependent shock position and velocity and the radius at which the shock stalls. Our results have implications for black hole formation and the newly detected class of fast X-ray transients (FXTs). In particular, we propose that a "phantom shock breakout"—where the outer edge of the star falls through a stalled shock—can yield a burst of X-rays without a subsequent optical/UV signature, similar to FXTs. This model predicts the rise time of the X-ray burst, t d, and the mean photon energy, kT, are anticorrelated, approximately as T ∝ t d − 5 / 8 . [ABSTRACT FROM AUTHOR]

The fate of stars in the zero-age main-sequence (ZAMS) range ≈8–12 M ⊙ is unclear. They could evolve to form white dwarfs or explode as electron-capture supernovae (SNe) or iron core-collapse SNe (CCSNe). Even though the initial mass function indicates that this mass range should account for over 40% of all CCSN progenitors, few have been observationally confirmed, likely due to the faintness and rapid evolution of some of these transients. In this paper, we present a sample of nine Ca-rich/O-poor Type IIb SNe detected by the Zwicky Transient Facility with progenitors likely in this mass range. These sources have a [Ca ii ] λ λ 7291, 7324/[O i ] λ λ 6300, 6364 flux ratio of ≳2 in their nebular spectra. Comparing the measured [O i ] luminosity (≲1039 erg s−1) and derived oxygen mass (≈0.01 M ⊙) with theoretical models, we infer that the progenitor ZAMS mass for these explosions is less than 12 M ⊙. The ejecta properties (M ej ≲ 1 M ⊙ and E kin ∼ 1050 erg) are also consistent. The low ejecta mass of these sources indicates a class of strongly-stripped SNe that is a transition between the regular stripped-envelope SNe and ultra-stripped SNe. The progenitor could be stripped by a main-sequence companion and result in the formation of a neutron star−main sequence binary. Such binaries have been suggested to be progenitors of neutron star−white dwarf systems that could merge within a Hubble time and be detectable with LISA. [ABSTRACT FROM AUTHOR]

We analyze the directional dependence of the gravitational wave (GW) emission from 15 3D neutrino radiation hydrodynamic simulations of core-collapse supernovae (CCSNe). Using spin weighted spherical harmonics, we develop a new analytic technique to quantify the evolution of the distribution of GW emission over all angles. We construct a physics-informed toy model that can be used to approximate GW distributions for general ellipsoid-like systems, and use it to provide closed form expressions for the distribution of GWs for different CCSN phases. Using these toy models, we approximate the protoneutron star (PNS) dynamics during multiple CCSN stages and obtain similar GW distributions to simulation outputs. When considering all viewing angles, we apply this new technique to quantify the evolution of preferred directions of GW emission. For nonrotating cases, this dominant viewing angle drifts isotropically throughout the supernova, set by the dynamical timescale of the PNS. For rotating cases, during core bounce and the following tens of milliseconds, the strongest GW signal is observed along the equator. During the accretion phase, comparable—if not stronger—GW amplitudes are generated along the axis of rotation, which can be enhanced by the low T /∣ W ∣ instability. We show two dominant factors influencing the directionality of GW emission are the degree of initial rotation and explosion morphology. Lastly, looking forward, we note the sensitive interplay between GW detector site and supernova orientation, along with its effect on detecting individual polarization modes. [ABSTRACT FROM AUTHOR]

Astrophysical explosions that contain dense and ram-pressure-dominated ejecta evolve through an interaction phase, during which a forward shock (FS), contact discontinuity (CD), and reverse shock (RS) form and expand with time. We describe new self-similar solutions that apply to this phase and are most accurate in the limit that the ejecta density is large compared to the ambient density. These solutions predict that the FS, CD, and RS expand at different rates in time and not as single temporal power laws, are valid for explosions driven by steady winds and homologously expanding ejecta, and exist when the ambient density profile is a power law with a power-law index shallower than ∼3 (specifically when the FS does not accelerate). We find excellent agreement between the predictions of these solutions and hydrodynamical simulations, both for the temporal behavior of the discontinuities and for the variation of the fluid quantities. The self-similar solutions are applicable to a wide range of astrophysical phenomena and—although the details are described in future work—can be generalized to incorporate relativistic speeds with arbitrary Lorentz factors. We suggest that these solutions accurately interpolate between the initial “coasting” phase of the explosion and the later, energy-conserving phase (or, if the ejecta is homologous and the density profile is sufficiently steep, the self-similar phase described in R. A. Chevalier).

Recent neutron star surface observations corroborate a long-standing theory that neutron stars may be accelerated over extended periods after their birth. We analyze how these prolonged rocket-like accelerations, combined with rapid birth kicks, impact binary orbits. We find that even a small contribution of rocket kicks combined with instantaneous natal kicks can allow binaries to reach period–eccentricity combinations unattainable in standard binary evolution models. We propose these kick + rocket combinations as a new channel to form wide low-eccentricity neutron star binaries such as Gaia NS1, as well as inducing stellar mergers months to years after a supernova to cause peculiar high-energy transients.

At least three members of the recently identified class of fast luminous blue optical transients show evidence of late-time electromagnetic activity in great excess of what was predicted by an extrapolation of the early time emission. In particular, AT2022tsd displays fast, bright optical fluctuations approximately a month after the initial detection. Here we propose that these transients are produced by exploding stars in black hole binary systems and that the late-time activity is due to the accretion of clumpy ejecta onto the companion black hole. We derive the energetics and timescales involved, compute the emission spectrum, and discuss whether the ensuing emission is diffused or not in the remnant. We find that this model can explain the observed range of behaviors for reasonable ranges of the orbital separation and the ejecta velocity and clumpiness. Close separation and clumpy, high-velocity ejecta result in bright variable emission, as seen in AT2022tsd. A wider separation and smaller ejecta velocity, conversely, give rise to fairly constant emission at a lower luminosity. We suggest that high-cadence, simultaneous, panchromatic monitoring of future transients should be carried out to better understand the origin of the late emission and the role of binarity in the diversity of explosive stellar transients.

We present James Webb Space Telescope (JWST) NIRCam and NIRSpec observations of a Type Ic supernova (SN Ic) and its host galaxy (JADES-GS+53.13533-27.81457) at z = 2.83. This SN (named SN 2023adta) was identified in deep JWST/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Follow-up observations with JWST/NIRSpec provided a spectroscopic redshift of z = 2.83 and the classification as an SN Ic-BL. The light curve of SN 2023adta matches well with other stripped-envelope SNe, and we find a high peak luminosity, M _V = −19.0 ± 0.2 mag, based on the distribution of best-fit SNe. The broad absorption features in its spectrum are consistent with other SNe Ic-BL 1–3 weeks after peak brightness. We measure a Ca ii near-IR triplet expansion velocity of 29,000 ± 2000 km s ^−1 . The host galaxy of SN 2023adta is irregular, and modeling of its spectral energy distribution indicates a metallicity of $Z={0.35}_{-0.08}^{+0.16}{Z}_{\odot }$ . This environment is consistent with the population of low- z SNe Ic-BL that prefer lower metallicities relative to other stripped-envelope SNe and track long-duration γ -ray burst environments. We do not identify any γ -ray bursts that are coincident with SN 2023adta. Given the rarity of SNe Ic-BL in the local Universe, the detection of an SN Ic-BL at z = 2.83 could indicate that their rates are enhanced at high redshift.

We present high-cadence photometric and spectroscopic observations of supernova (SN) 2024ggi, a Type II SN with flash spectroscopy features, which exploded in the nearby galaxy NGC 3621 at ∼7 Mpc. The light-curve evolution over the first 30 hr can be fit by two power-law indices with a break after 22 hr, rising from M _V ≈ −12.95 mag at +0.66 day to M _V ≈ −17.91 mag after 7 days. In addition, the densely sampled color curve shows a strong blueward evolution over the first few days and then behaves as a normal SN II with a redward evolution as the ejecta cool. Such deviations could be due to interaction with circumstellar material (CSM). Early high- and low-resolution spectra clearly show high-ionization flash features from the first spectrum to +3.42 days after the explosion. From the high-resolution spectra, we calculate the CSM velocity to be 37 ± 4 km s ^−1 . We also see the line strength evolve rapidly from 1.22 to 1.49 days in the earliest high-resolution spectra. Comparison of the low-resolution spectra with CMFGEN models suggests that the pre-explosion mass-loss rate of SN 2024ggi falls in the range of 10 ^−3 –10 ^−2 M _☉ yr ^−1 , which is similar to that derived for SN 2023ixf. However, the rapid temporal evolution of the narrow lines in the spectra of SN 2024ggi ( R _CSM ∼ 2.7 × 10 ^14 cm) could indicate a smaller spatial extent of the CSM than in SN 2023ixf ( R _CSM ∼ 5.4 × 10 ^14 cm), which in turn implies a lower total CSM mass for SN 2024ggi.

We present the first numerical study of gravitational waves (GWs) from collapsar disks, using state-of-the-art 3D general relativistic magnetohydrodynamic simulations of collapsing stars. These simulations incorporate a fixed Kerr metric for the central black hole (BH) and employ simplified prescriptions for disk cooling. We find that cooled disks with an expected scale height ratio of H / R ≳ 0.1 at ∼10 gravitational radii induce Rossby instability in compact, high-density rings. The trapped Rossby vortices generate vigorous coherent emission regardless of disk magnetization and BH spin. For BH mass of ∼10 M _⊙ , the GW spectrum peaks at ∼100 Hz, with some breadth due to various nonaxisymmetric modes. The spectrum shifts toward lower frequencies as the disk viscously spreads and the circularization radius of the infalling gas increases. Weaker-cooled disks with H / R ≳ 0.3 form a low-density extended structure of spiral arms, resulting in a broader, lower-amplitude spectrum. Assuming an optimistic detection threshold with a matched-filter signal-to-noise ratio of 20 and a rate similar to Type Ib/c supernovae, LIGO–Virgo–KAGRA (LVK) could detect ≲1 event annually, suggesting that GW events may already be hidden in observed data. Third-generation GW detectors could detect dozens to hundreds of collapsar disks annually, depending on the cooling strength and the disk formation rate. The GW amplitudes from collapsar disks are ≳100 times higher with a substantially greater event rate than those from core-collapse supernovae, making them potentially the most promising burst-type GW class for LVK and Cosmic Explorer. This highlights the importance of further exploration and modeling of disk-powered GWs, promising insights into collapsing star physics.

We present early-phase good-cadence (hour-to-day) simultaneous multiband ( ugi and vrz bands) imaging of the nearby supernova SN 2024ggi, which exploded in the nearby galaxy NGC 3621. A quick follow-up was conducted within less than a day after the explosion and continued for ∼23 days. The uvg band light curves display a rapid rise (∼1.4 mag day ^−1 ) to maximum in ∼4 days and absolute magnitude M _g ∼ −17.75 mag. The postpeak decay rate in redder bands is ∼0.01 mag day ^−1 . Different colors (e.g., u − g and v − r ) of SN 2024ggi are slightly redder than SN 2023ixf. A significant rise (∼12.5 kK) in blackbody temperature (optical) was noticed within ∼2 days after the explosion, which successively decreased, indicating shock break out inside a dense circumstellar medium surrounding the progenitor. Using semianalytical modeling, the ejecta mass and progenitor radius were estimated as 1.2 M _☉ and ∼550 R _☉ . The archival deep images ( g , r , i , and z bands) from the Dark Energy Camera Legacy Survey were examined, and a possible progenitor was detected in each band (∼22–22.5 mag) and had a mass range of 14–17 M _☉ .

We present early-time, hour-to-day cadence spectroscopy of the nearby Type II supernova (SN II) 2024ggi, which was discovered at a phase when the SN shock had just emerged from the red supergiant (RSG) progenitor star. Over the first few days after the first light, SN 2024ggi exhibited prominent narrow emission lines formed through intense and persistent photoionization of the nearby circumstellar material (CSM). In the first 63 hr, spectral lines of He, C, N, and O revealed a rapid rise in ionization as a result of the progressive sweeping up of the CSM by the shock. The duration of the IIn-like spectra indicates a dense and relatively confined CSM distribution extending up to ∼4 × 10 ^14 cm. Spectral modeling reveals that a CSM mass-loss rate at this region exceeding 5 × 10 ^−3 M _⊙ yr ^−1 is required to reproduce low-ionization emissions, which dramatically exceeds that of an RSG. Analyzing the H α emission shift implies the velocity of the unshocked outer CSM to be between 20 and 40 km s ^−1 , matching the typical wind velocity of an RSG. The differences between the inner and outer layers of the CSM and an RSG progenitor highlight a complex mass-loss history before the explosion of SN 2024ggi.

Type IIb supernovae are an important subclass of stripped-envelope supernovae (SNe), which show H lines only at early times. Their progenitors are believed to contain a low-mass H envelope before explosion. This work reports the discovery of a progenitor candidate in preexplosion Hubble Space Telescope images for the Type IIb SN 2017gkk. With detailed analysis of its spectral energy distribution and local environment, we suggest that the progenitor is most likely a yellow supergiant with significant circumstellar extinction and has an initial mass of about 16 M _⊙ , effective temperature log( T _eff /K) = 3.72 ± 0.08, and luminosity log( L / L _⊙ ) = 5.17 ± 0.04. This progenitor is not massive enough to strip envelope through stellar wind, and it supports an interacting binary progenitor channel and adds to the growing list of direct progenitor detections for Type IIb SNe. Future late-time observations will confirm whether this progenitor candidate has disappeared and reveal the putative binary companion that has survived the explosion.

We present SN 2023zaw—a subluminous ( M _r = −16.7 mag) and rapidly evolving supernova ( t _1/2, _r = 4.9 days), with the lowest nickel mass (≈0.002 M _⊙ ) measured among all stripped-envelope supernovae discovered to date. The photospheric spectra are dominated by broad He i and Ca near-infrared emission lines with velocities of ∼10,000−12,000 km s ^−1 . The late-time spectra show prominent narrow He i emission lines at ∼1000 km s ^−1 , indicative of interaction with He-rich circumstellar material. SN 2023zaw is located in the spiral arm of a star-forming galaxy. We perform radiation-hydrodynamical and analytical modeling of the lightcurve by fitting with a combination of shock-cooling emission and nickel decay. The progenitor has a best-fit envelope mass of ≈0.2 M _☉ and an envelope radius of ≈50 R _⊙ . The extremely low nickel mass and low ejecta mass (≈0.5 M _⊙ ) suggest an ultrastripped SN, which originates from a mass-losing low-mass He-star (zero-age main-sequence mass < 10 M _⊙ ) in a close binary system. This is a channel to form double neutron star systems, whose merger is detectable with LIGO. SN 2023zaw underscores the existence of a previously undiscovered population of extremely low nickel mass (

We present JWST observations of the Crab Nebula, the iconic remnant of the historical SN 1054. The observations include NIRCam and MIRI imaging mosaics plus MIRI/MRS spectra that probe two select locations within the ejecta filaments. We derive a high-resolution map of dust emission and show that the grains are concentrated in the innermost, high-density filaments. These dense filaments coincide with multiple synchrotron bays around the periphery of the Crab's pulsar wind nebula (PWN). We measure synchrotron spectral index changes in small-scale features within the PWN’s torus region, including the well-known knot and wisp structures. The index variations are consistent with Doppler boosting of emission from particles with a broken power-law distribution, providing the first direct evidence that the curvature in the particle injection spectrum is tied to the acceleration mechanism at the termination shock. We detect multiple nickel and iron lines in the ejecta filaments and use photoionization models to derive nickel-to-iron abundance ratios that are a factor of 3–8 higher than the solar ratio. We also find that the previously reported order-of-magnitude higher Ni/Fe values from optical data are consistent with the lower values from JWST when we reanalyze the optical emission using updated atomic data and account for local extinction from dust. We discuss the implications of our results for understanding the nature of the explosion that produced the Crab Nebula and conclude that the observational properties are most consistent with a low-mass Fe core-collapse supernova, even though an electron-capture explosion cannot be ruled out.

Type Icn supernovae (SNe Icn) are a newly detected, rare subtype of interacting stripped-envelope supernovae that show narrow P Cygni lines of highly ionized carbon, oxygen, and neon in their early spectra due to the interactions of the SNe ejecta with dense hydrogen- and helium-deficient circumstellar material (CSM). It has been suggested that SNe Icn may have multiple progenitor channels, such as the explosion of carbon-rich Wolf–Rayet stars or the explosion of stripped-envelope SNe, which undergo binary interactions. Among the SNe Icn, SN 2019jc shows unique properties, and previous work inferred that it may stem from the ultrastripped supernova, but other possibilities still exist. In this work, we aim to simulate the light curves from the explosions of oxygen-neon and carbon-oxygen double white dwarf (WD) merger remnants and to further investigate whether the corresponding explosions can appear as some particular SNe Icn. We generate the light curves from the explosive remnants and analyze the influence of different parameters on the light curves, such as the ejecta mass, explosion energy, mass of ^56 Ni, and CSM properties. Comparing our results with some SNe Icn, we found that the light curves from the explosions of double WD merger remnants can explain the observable properties of SN 2019jc, from which we infer that this special SN Icn may have a different progenitor. Our results indicate that double WD merger may be an alternative model in producing at least one of the SNe Icn.

Type IIn supernovae (SNe) exhibit narrow hydrogen lines that arise from the strong interaction between ejecta and circumstellar material. It remains poorly understood, however, what progenitor stars give rise to these explosions. In this work, we perform a detailed analysis of the progenitor and environment of the nearby Type IIn SN 2010jl. With newer images taken by the Hubble Space Telescope, we confirm that the previously reported progenitor candidate is a blend of the progenitor itself and a field star cluster in its close vicinity. SN 2010jl has now become much fainter than the progenitor. The progenitor is very blue and luminous with an effective temperature of log T _eff /K = 4.26 ${}_{-0.09}^{+0.11}$ and a luminosity of log L / L _⊙ = 6.52 ${}_{-0.16}^{+0.20}$ . It is located in a very young star-forming region, but its luminosity is much higher than that expected from the environmental stellar populations. We suggest that the progenitor was in outburst when observed. Its nature and evolutionary history remain to be investigated.

We present initial results from a James Webb Space Telescope (JWST) survey of the youngest Galactic core-collapse supernova remnant, Cassiopeia A (Cas A), made up of NIRCam and MIRI imaging mosaics that map emission from the main shell, interior, and surrounding circumstellar/interstellar material (CSM/ISM). We also present four exploratory positions of MIRI Medium Resolution Spectrograph integral field unit spectroscopy that sample ejecta, CSM, and associated dust from representative shocked and unshocked regions. Surprising discoveries include (1) a weblike network of unshocked ejecta filaments resolved to ∼0.01 pc scales exhibiting an overall morphology consistent with turbulent mixing of cool, low-entropy matter from the progenitor’s oxygen layer with hot, high-entropy matter heated by neutrino interactions and radioactivity; (2) a thick sheet of dust-dominated emission from shocked CSM seen in projection toward the remnant’s interior pockmarked with small (∼1″) round holes formed by ≲0.″1 knots of high-velocity ejecta that have pierced through the CSM and driven expanding tangential shocks; and (3) dozens of light echoes with angular sizes between ∼0.″1 and 1′ reflecting previously unseen fine-scale structure in the ISM. NIRCam observations place new upper limits on infrared emission (≲20 nJy at 3 μ m) from the neutron star in Cas A’s center and tightly constrain scenarios involving a possible fallback disk. These JWST survey data and initial findings help address unresolved questions about massive star explosions that have broad implications for the formation and evolution of stellar populations, the metal and dust enrichment of galaxies, and the origin of compact remnant objects.

The apparent tension between the luminosity functions of red supergiant (RSG) stars and of RSG progenitors of Type II supernovae (SNe) is often referred to as the RSG problem and it motivated some to suggest that many RSGs end their life without an SN explosion. However, the luminosity functions of RSG SN progenitors presented so far were biased to high luminosities, because the sensitivity of the search was not considered. Here, we use limiting magnitudes to calculate a bias-corrected RSG progenitor luminosity function. We find that only (36 ± 11)% of all RSG progenitors are brighter than a bolometric magnitude of −7 mag, a significantly smaller fraction than (56 ± 5)% quoted by Davies & Beasor. The larger uncertainty is due to the relatively small progenitor sample, while uncertainties on measured quantities such as magnitudes, bolometric corrections, extinction, or SN distances, only have a minor impact, as long as they fluctuate randomly for different objects in the sample. The bias-corrected luminosity functions of RSG SN progenitors and Type M supergiants in the Large Magellanic Cloud are consistent with each other, as also found by Davies & Beasor for the uncorrected luminosity function. The RSG progenitor luminosity function, hence, does not imply the existence of failed SNe. The presented statistical method is not limited to progenitor searches, but applies to any situation in which a measurement is done for a sample of detected objects, but the probed quantity or property can only be determined for part of the sample.

AT2018cow is the most extensively observed and widely studied fast blue optical transient to date; its unique observational properties challenge all existing standard models. In this paper, we model the luminosity evolution of the optical, soft X-ray, and hard X-ray emission, as well as the X-ray spectrum of AT2018cow with a magnetar-centered engine model. We consider a two-zone model with a striped magnetar wind in the interior and an expanding ejecta outside. The soft and hard X-ray emission of AT2018cow can be explained by the leakage of high-energy photons produced by internal gradual magnetic dissipation in the striped magnetar wind, while the luminous thermal UV/optical emission results from the thermalization of the ejecta by the captured photons. The two-component energy spectrum yielded by our model with a quasi-thermal component from the optically thick region of the wind superimposed on an optically thin synchrotron component well reproduces the X-ray spectral shape of AT2018cow. The Markov Chain Monte Carlo fitting results suggest that in order to explain the very short rise time to peak of the thermal optical emission, a low ejecta mass M _ej ≈ 0.1 M _⊙ and high ejecta velocity ${v}_{\mathrm{SN}}\approx 0.17c$ are required. A millisecond magnetar with P _0 ≈ 3.7 ms and B _p ≈ 2.4 × 10 ^14 G is needed to serve as the central engine of AT2018cow.

Stars that formed with an initial mass of over 50 M _⊙ are very rare today, but they are thought to be more common in the early Universe. The fates of those early, metal-poor, massive stars are highly uncertain. Most are expected to directly collapse to black holes, while some may explode as a result of rotationally powered engines or the pair-creation instability. We present the chemical abundances of J0931+0038, a nearby low-mass star identified in early follow-up of the SDSS-V Milky Way Mapper, which preserves the signature of unusual nucleosynthesis from a massive star in the early Universe. J0931+0038 has a relatively high metallicity ([Fe/H] = −1.76 ± 0.13) but an extreme odd–even abundance pattern, with some of the lowest known abundance ratios of [N/Fe], [Na/Fe], [K/Fe], [Sc/Fe], and [Ba/Fe]. The implication is that a majority of its metals originated in a single extremely metal-poor nucleosynthetic source. An extensive search through nucleosynthesis predictions finds a clear preference for progenitors with initial mass >50 M _⊙ , making J0931+0038 one of the first observational constraints on nucleosynthesis in this mass range. However, the full abundance pattern is not matched by any models in the literature. J0931+0038 thus presents a challenge for the next generation of nucleosynthesis models and motivates the study of high-mass progenitor stars impacted by convection, rotation, jets, and/or binary companions. Though rare, more examples of unusual early nucleosynthesis in metal-poor stars should be found in upcoming large spectroscopic surveys.

We report observations of the optical counterpart of the long gamma-ray burst (GRB) GRB 230812B and its associated supernova (SN) SN 2023pel. The proximity ( z = 0.36) and high energy ( E _γ _,iso ∼ 10 ^53 erg) make it an important event to study as a probe of the connection between massive star core collapse and relativistic jet formation. With a phenomenological power-law model for the optical afterglow, we find a late-time flattening consistent with the presence of an associated SN. SN 2023pel has an absolute peak r -band magnitude of M _r = −19.46 ± 0.18 mag (about as bright as SN 1998bw) and evolves on quicker timescales. Using a radioactive heating model, we derive a nickel mass powering the SN of M _Ni = 0.38 ± 0.01 M _⊙ and a peak bolometric luminosity of L _bol ∼ 1.3 × 10 ^43 erg s ^−1 . We confirm SN 2023pel’s classification as a broad-line Type Ic SN with a spectrum taken 15.5 days after its peak in the r band and derive a photospheric expansion velocity of v _ph = 11,300 ± 1600 km s ^−1 at that phase. Extrapolating this velocity to the time of maximum light, we derive the ejecta mass M _ej = 1.0 ± 0.6 M _⊙ and kinetic energy ${E}_{\mathrm{KE}}={1.3}_{-1.2}^{+3.3}\times {10}^{51}\,\mathrm{erg}$ . We find that GRB 230812B/SN 2023pel has SN properties that are mostly consistent with the overall GRB-SN population. The lack of correlations found in the GRB-SN population between SN brightness and E _γ _,iso for their associated GRBs across a broad range of 7 orders of magnitude provides further evidence that the central engine powering the relativistic ejecta is not coupled to the SN powering mechanism in GRB-SN systems.

We have simulated the collapse and evolution of the core of a solar-metallicity 40 M ⊙ star and find that it explodes vigorously by the neutrino mechanism, despite its very high "compactness." Within ∼1.5 s of explosion, a black hole forms. The explosion is very asymmetrical and has a total explosion energy of ∼1.6 × 1051 erg. At black hole formation, its baryon mass is ∼2.434 M ⊙ and gravitational mass is 2.286 M ⊙. Seven seconds after black hole formation, an additional ∼0.2 M ⊙ is accreted, leaving a black hole baryon mass of ∼2.63 M ⊙. A disk forms around the proto−neutron star, from which a pair of neutrino-driven jets emanates. These jets accelerate some of the matter up to speeds of ∼45,000 km s−1 and contain matter with entropies of ∼50. The large spatial asymmetry in the explosion results in a residual black hole recoil speed of ∼1000 km s−1. This novel black hole formation channel now joins the other black hole formation channel between ∼12 and ∼15 M ⊙ discovered previously and implies that the black hole/neutron star birth ratio for solar-metallicity stars could be ∼20%. However, one channel leaves black holes in perhaps the ∼5–15 M ⊙ range with low kick speeds, while the other leaves black holes in perhaps the ∼2.5–3.0 M ⊙ mass range with high kick speeds. However, even ∼8.8 s after core bounce the newly formed black hole is still accreting at a rate of ∼2 × 10−2 M ⊙ s−1, and whether the black hole eventually achieves a significantly larger mass over time is yet to be determined. [ABSTRACT FROM AUTHOR]

Core-collapse supernovae (SNe) are one of the most powerful cosmic sources of neutrinos, with energies of several MeV. The emission of neutrinos and antineutrinos of all flavors carries away the gravitational binding energy of the compact remnant and drives its evolution from the hot initial to the cold final states. Detecting these neutrinos from Earth and analyzing the emitted signals present a unique opportunity to explore the neutrino mass ordering problem. This research outlines the detection of neutrinos from SNe and their relevance in understanding the neutrino mass ordering. The focus is on developing a model-independent analysis strategy, achieved by comparing distinct detection channels in large underground detectors. The objective is to identify potential indicators of mass ordering within the neutrino sector. Additionally, a thorough statistical analysis is performed on the anticipated neutrino signals for both mass orderings. Despite uncertainties in supernova explosion parameters, an exploration of the parameter space reveals an extensive array of models with significant sensitivity to differentiate between mass orderings. The assessment of various observables and their combinations underscores the potential of forthcoming supernova observations in addressing the neutrino mass ordering problem. [ABSTRACT FROM AUTHOR]

We perform a comprehensive search for optical precursor emission at the position of SN 2023ixf using data from the DLT40, ZTF, and ATLAS surveys. By comparing the current data set with precursor outburst hydrodynamical model light curves, we find that the probability of a significant outburst within 5 yr of explosion is low, and the circumstellar material (CSM) ejected during any possible precursor outburst is likely smaller than ∼0.015 M ⊙. By comparing to a set of toy models, we find that, if there was a precursor outburst, the duration must have been shorter than ∼100 days for a typical brightness of M r ≃ −9 mag or shorter than 200 days for M r ≃ −8 mag; brighter, longer outbursts would have been discovered. Precursor activity like that observed in the normal Type II SN 2020tlf (M r ≃ −11.5) can be excluded in SN 2023ixf. If the dense CSM inferred by early flash spectroscopy and other studies is related to one or more precursor outbursts, then our observations indicate that any such outburst would have to be faint and only last for days to months, or it occurred more than 5 yr prior to the explosion. Alternatively, any dense, confined CSM may not be due to eruptive mass loss from a single red supergiant progenitor. Taken together, the results of SN 2023ixf and SN 2020tlf indicate that there may be more than one physical mechanism behind the dense CSM inferred around some normal Type II supernovae. [ABSTRACT FROM AUTHOR]

We explore a possible explosion scenario resulting from core collapses of rotating massive stars that leave a black hole by performing radiation-viscous-hydrodynamics simulations in numerical relativity. We take moderately and rapidly rotating compact pre-collapse stellar models with zero-age main-sequence masses of 9 M ⊙ and 20 M ⊙ based on stellar evolution calculations as the initial conditions. We find that viscous heating in the disk formed around the central black hole is the power source for an outflow. The moderately rotating models predict a small ejecta mass of the order of 0.1 M ⊙ and an explosion energy of ≲1051 erg. Due to the small ejecta mass, these models may predict a short-timescale transient with a rise time of 3–5 days. This can lead to a bright (∼1044 erg s−1) transient, like superluminous supernovae in the presence of a dense massive circumstellar medium. For hypothetically rapidly rotating models that have a high mass-infall rate onto the disk, the explosion energy is ≳3 × 1051 erg, which is comparable to or larger than that of typical stripped-envelope supernovae, indicating that a fraction of such supernovae may be explosions powered by black hole accretion disks. The explosion energy is still increasing at the end of the simulations with a rate of >1050 erg s−1, and thus, it may reach ∼1052 erg. A nucleosynthesis calculation shows that the mass of 56Ni amounts to ≳0.1 M ⊙, which, together with the high explosion energy, may satisfy the required amount for broad-lined type Ic supernovae. Irrespective of the models, the lowest value of the electron fraction of the ejecta is ≳0.4; thus, synthesis of heavy r -process elements is not found in our models. [ABSTRACT FROM AUTHOR]

The emission from shock breakouts (SBOs) represents the earliest electromagnetic (EM) signal emitted by cataclysmic events involving the formation or the merger of neutron stars (NSs). As such, SBOs carry unique information on the structure of their progenitors and on the explosion energy. The characteristic SBO emission is expected in the UV range, and its detection is one of the key targets of the ULTRASAT satellite. Among SBO sources, we focus on a specific class involving the formation of fast-spinning magnetars in the core-collapse of massive stars. Fast-spinning magnetars are expected to produce a specific signature in the early UV supernova light curve, powered by the extra spin energy quickly released by the NS. Moreover, they are considered as optimal candidates for the emission of long-transient gravitational wave (GW) signals, the detection of which requires early EM triggers to boost the sensitivity of dedicated GW search pipelines. We calculate early supernova UV light curves in the presence of a magnetar central engine, as a function of the explosion energy, ejecta mass, and magnetar parameters. We then estimate the ULTRASAT detection horizon (z < 0.15) as a function of the same physical parameters, and the overall expected detection rate, finding that magnetar-powered SBOs may represent up to 1/5 of the total events detected by ULTRASAT. Moreover, at the expected sensitivity of the LIGO/Virgo/Kagra O5 science run, one such event occurring within 5 Mpc will provide an ideal trigger for a GW long-transient search. Future GW detectors like the Einstein Telescope will push the horizon for joint EM-GW detections to 35–40 Mpc. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the neutrino-driven winds that emerge in 12 unprecedentedly long-duration 3D core-collapse supernova simulations done using the code F ornax. The 12 models cover progenitors with zero-age main-sequence mass between 9 and 60 solar masses. In all our models, we see transonic outflows that are at least 2 times as fast as the surrounding ejecta and that originate generically from a proto−neutron star surface atmosphere that is turbulent and rotating. We find that winds are common features of 3D simulations, even if there is anisotropic early infall. We find that the basic dynamical properties of 3D winds behave qualitatively similarly to those inferred in the past using simpler 1D models, but that the shape of the emergent wind can be deformed, very aspherical, and channeled by its environment. The thermal properties of winds for less massive progenitors very approximately recapitulate the 1D stationary solutions, while for more massive progenitors they deviate significantly owing to aspherical accretion. The Y e temporal evolution in winds is stochastic, and there can be some neutron-rich phases. Though no strong r -process is seen in any model, a weak r -process can be produced, and isotopes up to 90Zr are synthesized in some models. Finally, we find that there is at most a few percent of a solar mass in the integrated wind component, while the energy carried by the wind itself can be as much as 10%–20% of the total explosion energy. [ABSTRACT FROM AUTHOR]

Interaction-powered supernovae (SNe) explode within an optically thick circumstellar medium (CSM) that could be ejected during eruptive events. To identify and characterize such pre-explosion outbursts, we produce forcedphotometry light curves for 196 interacting SNe, mostly of Type IIn, detected by the Zwicky Transient Facility between early 2018 and 2020 June. Extensive tests demonstrate that we only expect a few false detections among the 70,000 analyzed pre-explosion images after applying quality cuts and bias corrections. We detect precursor eruptions prior to 18 Type IIn SNe and prior to the Type Ibn SN 2019uo. Precursors become brighter and more frequent in the last months before the SN and month-long outbursts brighter than magnitude -13 occur prior to 25% (5-69%, 95% confidence range) of all Type IIn SNe within the final three months before the explosion. With radiative energies of up to 1049erg, precursors could eject ~1M⊙of material. Nevertheless, SNe with detected precursors are not significantly more luminous than other SNe IIn, and the characteristic narrow hydrogen lines in their spectra typically originate from earlier, undetected mass-loss events. The long precursor durations require ongoing energy injection, and they could, for example, be powered by interaction or by a continuum-driven wind. Instabilities during the neon- and oxygen-burning phases are predicted to launch precursors in the final years to months before the explosion; however, the brightest precursor is 100 times more energetic than anticipated.

The Cassiopeia A supernova remnant has a complex structure, manifesting the multidimensional nature of core-collapse supernova explosions. To further understand this, we carried out near-infrared multiobject spectroscopy on the ejecta knots located in the northeastern (NE) jet and Fe K plume regions, which are two distinct features in the outer eastern area of the remnant. Our study reveals that the knots exhibit varying ratios of [S ii ] 1.03, [P ii ] 1.189, and [Fe ii ] 1.257 μ m lines depending on their locations within the remnant, suggesting regional differences in elemental composition. Notably, the knots in the NE jet are mostly S-rich with weak or no [P ii ] lines, implying that they originated below the explosive Ne-burning layer, consistent with the results of previous studies. We detected no ejecta knots exhibiting only [Fe ii ] lines in the NE jet area that are expected in the jet-driven supernova explosion model. Instead, we discovered a dozen Fe-rich knots in the Fe K plume area. We propose that they are dense knots produced by a complete Si burning with α -rich freeze-out in the innermost region of the progenitor and ejected with the diffuse X-ray-emitting Fe ejecta but decoupled after crossing the reverse shock. In addition to these metal-rich ejecta knots, several knots emitting only He i 1.083 μ m lines were detected, and their origin remains unclear. We also detected three extended H emission features of circumstellar or interstellar origin in this area and discuss their association with the supernova remnant. [ABSTRACT FROM AUTHOR]

The astrophysical environments capable of triggering heavy-element synthesis via rapid neutron capture (the r -process) remain uncertain. While binary neutron star mergers (NSMs) are known to forge r -process elements, certain rare supernovae (SNe) have been theorized to supplement—or even dominate— r -production by NSMs. However, the most direct evidence for such SNe, unusual reddening of the emission caused by the high opacities of r -process elements, has not been observed. Recent work identified the distribution of r -process material within the SN ejecta as a key predictor of the ease with which signals associated with r -process enrichment could be discerned. Though this distribution results from hydrodynamic processes at play during the SN explosion, thus far it has been treated only in a parameterized way. We use hydrodynamic simulations to model how disk winds—the alleged locus of r -production in rare SNe—mix with initially r -process-free ejecta. We study mixing as a function of the wind mass, wind duration, and the initial SN explosion energy, and find that it increases with the first two of these and decreases with the third. This suggests that SNe accompanying the longest long-duration gamma-ray bursts are promising places to search for signs of r -process enrichment. We use semianalytic radiation transport to connect hydrodynamics to electromagnetic observables, allowing us to assess the mixing level at which the presence of r -process material can be diagnosed from SN light curves. Analytic arguments constructed atop this foundation imply that a wind-driven r -process-enriched SN model is unlikely to explain standard energetic SNe. [ABSTRACT FROM AUTHOR]

The introduction of deep wide-field surveys in recent years and the adoption of machine-learning techniques have led to the discoveries of  (10 4) strong gravitational lensing systems and candidates. However, the discovery of multiply-lensed transients remains a rarity. Lensed transients and especially lensed supernovae are invaluable tools to cosmology because they allow us to constrain cosmological parameters via lens modeling and the measurements of their time delays. In this paper, we develop a pipeline to perform a targeted lensed transient search. We apply this pipeline to 5807 strong lenses and candidates, which were identified in the literature, in the DESI Legacy Imaging Surveys Data Release 9 (DR9) footprint. For each system, we analyze every exposure in all of the observed bands (DECam g, r, and z). Our pipeline finds, groups, and ranks detections that are in sufficient proximity temporally and spatially. After the first round of inspection, for promising candidate systems, we further examine the newly available DR10 data (with additional i and Y bands). Here we present our targeted lensed supernova search pipeline and seven new lensed supernova candidates, including a very likely lensed supernova—probably a Type Ia—in a system with an Einstein radius of ∼1.″5. [ABSTRACT FROM AUTHOR]

The dynamics and spectral characteristics of supernova ejecta reveal details of the supernova energetics, explosive nucleosynthesis, and evolution of the progenitor. However, in practice, this important diagnostic information is only derived from CCD-resolution X-ray spectra of shock-heated material. If the spectra were to be observed at higher resolution, then important clues to the explosion energetics would be obvious through measurements of bulk Doppler motions and turbulence in the ejecta. Likewise, the unshocked ejecta in supernovae and young remnants are responsible for obscuring the emission from ejecta on the back side of the remnant. In light of these important effects, we present line-of-sight spectral maps of core-collapse supernova remnant models. We explore the bulk Doppler broadening of spectral lines, including line-of-sight effects. We also explore the time-dependent absorption from both shocked and unshocked ejecta. Finally, we discuss how future X-ray missions such as XRISM and Athena will be able to resolve these effects in nearby and extragalactic supernovae and their remnants. [ABSTRACT FROM AUTHOR]

We present observations of a peculiar hydrogen- and helium-poor stripped-envelope (SE) supernova (SN) 2020wnt, primarily in the optical and near-infrared (near-IR). Its peak absolute bolometric magnitude of −20.9 mag (L bol, peak = (6.8 ± 0.3) × 1043 erg s−1) and a rise time of 69 days are reminiscent of hydrogen-poor superluminous SNe (SLSNe I), luminous transients potentially powered by spinning-down magnetars. Before the main peak, there is a brief peak lasting <10 days post explosion, likely caused by interaction with circumstellar medium (CSM) ejected ∼years before the SN explosion. The optical spectra near peak lack a hot continuum and O ii absorptions, which are signs of heating from a central engine; they quantitatively resemble those of radioactivity-powered hydrogen/helium-poor Type Ic SESNe. At ∼1 yr after peak, nebular spectra reveal a blue pseudo-continuum and narrow O i recombination lines associated with magnetar heating. Radio observations rule out strong CSM interactions as the dominant energy source at +266 days post peak. Near-IR observations at +200–300 days reveal carbon monoxide and dust formation, which causes a dramatic optical light-curve dip. Pair-instability explosion models predict slow light curve and spectral features incompatible with observations. SN 2020wnt is best explained as a magnetar-powered core-collapse explosion of a 28 M ⊙ pre-SN star. The explosion kinetic energy is significantly larger than the magnetar energy at peak, effectively concealing the magnetar-heated inner ejecta until well after peak. SN 2020wnt falls into a continuum between normal SNe Ic and SLSNe I, and demonstrates that optical spectra at peak alone cannot rule out the presence of a central engine. [ABSTRACT FROM AUTHOR]

Type Ib and Ic supernovae (SNe Ib/Ic) originate from hydrogen-deficient massive star progenitors, of which the exact properties are still much debated. Using SN data in the literature, we investigate the optical B − V color of SNe Ib/Ic at the V -band peak and show that SNe Ib are systematically bluer than SNe Ic. We construct SN models from helium-rich and helium-poor progenitors of various masses using the radiation hydrodynamics code STELLA and discuss how the B − V color at the V -band peak is affected by the 56Ni to ejecta mass ratio, 56Ni mixing, and the presence/absence of a helium envelope. We argue that the dichotomy in the amount of helium in the progenitors plays the primary role in making the observed systematic color difference at the optical peak, in favor of the most commonly invoked SN scenario that SNe Ib and SNe Ic progenitors are helium rich and helium poor, respectively. [ABSTRACT FROM AUTHOR]

Cosmic multimessenger backgrounds include relic diffuse components created in the early universe and contributions from individual sources. Here, we study both type Ia supernovae (SNe Ia) and core-collapse supernovae (CCSNe) contributions to the diffuse neutrino and gamma-ray backgrounds in the MeV regime referred to as DSNB and DSGB respectively. We show that the diffuse SN Ia background is 106 times lower (for ν ¯ e ) than the CCSN background making it negligible. Our predicted DSNB ν ¯ e flux at earth in the 19.3–32 MeV regime is 0.36 ν cm−2 s−1. We also find that the DSNB flux in the energy range from 11.3 to 32 MeV varies by +29% with a change in the SFRD model from Madau & Fragos which yielded a minimum predicted flux, to the extragalactic background light reconstruction model (maximum predicted flux). The diffuse SN Ia gamma-ray background and its dependence on the progenitor supernova delay time distribution are also evaluated. Furthermore, we address the origin of the CGB (Cosmic Gamma-ray Background) in the 0.1–7 MeV regime by adding contributions from sources such as SNe Ia, CCSNe, radio-quiet Active Galactic Nuclei, Flat spectrum radio quasars (FSRQs) and Neutron star—neutron star mergers. We find that our modeled background (including uncertainties) matches the observed CGB above 1.0 MeV, but is a factor ≈2 lower than the observed flux in the 0.1–1.0 MeV range, highlighting the need for future MeV missions to establish the CGB spectrum more reliably, and to possibly identify additional sources or even source classes in the underexplored MeV band. [ABSTRACT FROM AUTHOR]

We present near-infrared (NIR) and optical observations of the Type Ic supernova (SN Ic) SN 2021krf obtained between days 13 and 259 at several ground-based telescopes. The NIR spectrum at day 68 exhibits a rising K -band continuum flux density longward of ∼2.0 μ m, and a late-time optical spectrum at day 259 shows strong [O i ] 6300 and 6364 Å emission-line asymmetry, both indicating the presence of dust, likely formed in the SN ejecta. We estimate a carbon-grain dust mass of ∼2 × 10−5 M ⊙ and a dust temperature of ∼900–1200 K associated with this rising continuum and suggest the dust has formed in SN ejecta. Utilizing the one-dimensional multigroup radiation-hydrodynamics code STELLA, we present two degenerate progenitor solutions for SN 2021krf, characterized by C–O star masses of 3.93 and 5.74 M ⊙, but with the same best-fit 56Ni mass of 0.11 M ⊙ for early times (0–70 days). At late times (70–300 days), optical light curves of SN 2021krf decline substantially more slowly than those expected from 56Co radioactive decay. Lack of H and He lines in the late-time SN spectrum suggests the absence of significant interaction of the ejecta with the circumstellar medium. We reproduce the entire bolometric light curve with a combination of radioactive decay and an additional powering source in the form of a central engine of a millisecond pulsar with a magnetic field smaller than that of a typical magnetar. [ABSTRACT FROM AUTHOR]

We present optical, radio, and X-ray observations of SN 2020bvc (=ASASSN-20bs, ZTF 20aalxlis), a nearby broad-line (BL) Type Ic supernova (SN) and the first double-peaked Ic-BL discovered without a gamma-ray burst (GRB) trigger. Our observations show that SN 2020bvc shares several properties in common with the Ic-BL SN 2006aj, which was associated with the low-luminosity gamma-ray burst (LLGRB) 060218. First, the 10 GHz radio luminosity is brighter than ordinary core-collapse SNe but fainter than LLGRB SNe such as SN 1998bw (associated with LLGRB 980425). We model our VLA observations (spanning 13-43 days) as synchrotron emission from a mildly relativistic (v 0.3c) forward shock. Second, with Swift and Chandra, we detect X-ray emission (L X 1041 erg that is not naturally explained as inverse Compton emission or part of the same synchrotron spectrum as the radio emission. Third, high-cadence (6× night-1) data from the Zwicky Transient Facility (ZTF) show a double-peaked optical light curve, the first peak from shock cooling of extended low-mass material (mass SN 2020bvc is the first double-peaked Ic-BL SN discovered without a GRB trigger, so it is noteworthy that it shows X-ray and radio emission similar to LLGRB SNe. For four of the five other nearby (z ≲ 0.05) Ic-BL SNe with ZTF high-cadence data, we rule out a first peak like that seen in SN 2006aj and SN 2020bvc, i.e., that lasts 1 day and reaches a peak luminosity M -18. Follow-up X-ray and radio observations of Ic-BL SNe with well-sampled early optical light curves will establish whether double-peaked optical light curves are indeed predictive of LLGRB-like X-ray and radio emission.