arXiv subjects

Evan O'Connor

Publications and source records attributed to Evan O'Connor.

At least 19 recordsLinked to original sources

arXiv2026

A Three-Dimensional Exploration of Magnetic Fields, Rotation, and Shock Revival in a $39 M_\odot$ Core-Collapse Supernova Progenitor

We present three-dimensional hydrodynamic and magnetohydrodynamic core-collapse supernova simulations of a rapidly rotating, high-compactness $39 M_\odot$ progenitor to investigate the roles of rotation and magnetic fields in shock revival and outflow morphology. This study is designed to separate neutrino-driven expansion, rotation-induced deformation, and magnetically aided polar outflow within the same progenitor. We evolve three models: a non-rotating hydrodynamic baseline, a rotating hydrodynamic model, and a rotating magnetized model. All three models reach runaway shock expansion within the simulated interval, but with markedly different morphologies and timescales. The magnetized model revives first and develops the clearest bipolar outflow. The rotating non-magnetized model undergoes the latest shock revival and remains comparatively compact at the end of the simulation. The non-rotating model also undergoes shock revival, but subsequently collapses to a black hole about one second after core bounce. In the magnetized model, Maxwell stresses redistribute angular momentum and extract energy from the differential rotation of the protoneutron star, reducing the inner-core spin and helping channel rotational free energy into the emerging polar outflow. Neutrino emission provides an additional, though smaller, angular-momentum sink in both rotating models. We find that rapid rotation and strong magnetic fields can launch an early magnetically aided polar outflow in 3D, while the resulting dynamics remain intrinsically non-axisymmetric. In this extreme progenitor, rotation also provides significant support against prompt black-hole formation, although the longer-term remnant stability remains uncertain beyond the simulated interval.

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arXiv2026

Black Hole Supernovae Outcomes Across a Wide Progenitor Range

Black hole supernovae (BHSNe), the term we use for core-collapse events in which black hole (BH) formation occurs after shock revival but before the explosion is complete, have emerged as a natural outcome of multidimensional simulations as these calculations have been extended to seconds after bounce. Yet they remain one of the least studied outcomes of core collapse. Here, we assess whether they are confined to the most compact and massive progenitors, whose birth rates are low, or whether they arise systematically across a wider range of progenitor structures. We perform 23 long-term axisymmetric core-collapse simulations of progenitors spanning 19.51-60$\,M_\odot$ and compactnesses $0.31 \lesssim \xi_{2.5} \lesssim 0.63$. We find 18 BHSN outcomes across nearly the full ZAMS mass range considered, corresponding to progenitors with $0.40 \lesssim \xi_{2.5} \lesssim 0.63$. BH formation occurs between $\sim0.7$ s and $\sim4.4$ s after bounce. After BH formation, we continue the evolution with an excision treatment to at least 5000 s. The final explosion energies span $\sim2\times10^{49}$-$3\times10^{51}$ erg, while the final BH gravitational masses span $\sim3$-$26\,M_\odot$. We find a clear remnant-mass trend with CO-core mass, but show that the CO core alone is not an adequate proxy for the final BH mass, especially for progenitors at the low- and high-mass ends of the CO-core distribution. Except for the highest CO-core mass models, no single spherical mass coordinate cleanly separates ejecta from remnant material. Finally, a 2D axisymmetric and a 3D model are compared as we discuss differences between the two geometries.

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arXiv2025

Prospects for detecting periodic or sharp fast-time features in the supernova neutrino lightcurve with IceCube

Neutrinos produced in core-collapse supernova offer a direct probe into the hydrodynamics and energy transport mechanisms during the collapse and play a pivotal role in the shock revival and success of the supernova explosion. Fast-time features of the neutrino luminosity and energy spectrum encode information about phenomena such as turbulence, convection, shock revival and potential quark-hadron phase transitions. In this study, we explore the detection capabilities of large-volume neutrino telescopes with a focus on IceCube and the planned extension IceCube-Gen2. Furthermore, we consider the effect on the detection sensitivity from wavelength shifters through enhanced light collection. A variety of models predict periodic fast-time features in supernova light curves; to quantify their detectability without relying on specific models, we investigate the detector response to a generic parameterisation of such features. We find that independent of feature frequency, IceCube-Gen2 instrumented with wavelength shifters has sensitivity to weaker modulations ($>25\%$ amplitude) as compared to only the strongest modulations ($>50\%$ amplitude) with IceCube. In addition, we examine the sensitivity of the neutrino lightcurve to sharp features from a quark-hadron phase transition. Phase transitions leading to a quark star remnant are detectable with IceCube at $5σ$ up to the edge of the Galaxy, and throughout the Small Magellanic Cloud with IceCube-Gen2 equipped with wavelength-shifters. In contrast, models collapsing into a black hole are observable only within the Galaxy, covering $41\%$ of the CCSNe population for IceCube and nearly all ($91\%$) for IceCube-Gen2 complemented by wavelength shifters. These results highlight the potential of IceCube-Gen2 for detecting Galactic sources more reliably and with greater reach.

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arXiv2025

A new approximation for heavy-lepton neutrino pair processes in simulations of core-collapse supernovae

In this paper, we present a new approximation for efficiently and effectively including heavy-lepton neutrino pair-production processes in neutrino transport simulations of core-collapse supernovae. In the neutrino-driven explosion mechanism, the electron neutrinos and anti-neutrinos are the main players in transporting the energy of the cooling PNS to the matter behind the shock. While heavy-lepton neutrinos, $ν_x$, play a smaller role in the heating of the gain region, they dominate the cooling of the proto-neutron star (PNS) and therefore still play a crucial role in the explosion mechanism. In this study, we explore the impacts of modifications in the transport and formalisms of pair ($ν_x\barν_x$) emission and absorption processes. We quantify the impact in terms of the emergent neutrino signal and the nature of the PNS convection and early cooling. For this, we perform a set of simulations, spherically symmetric and axisymmetric, of a 20 M$_\odot$ progenitor using two different state-of-the-art equations of state (EOS). First and foremost, we show that our new efficient approximation for neutrino pair production matches the results of a full treatment very well. Furthermore, for this progenitor, we show that the impact of the modifications is dependent on the EOS used, as the EOS drives the PNS evolution. The variations we explore, including variations due to the nucleon-nucleon bremsstrahlung formalism, have a comparatively smaller impact than the EOS has as a whole.

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arXiv2024

Black Hole Supernovae, their Equation of State Dependence and Ejecta Composition

Recent literature on core-collapse supernovae suggests that a black hole (BH) can form within $\sim 1$ s of shock revival, while still culminating in a successful supernova. We refer to these as black hole supernovae, as they are distinct from other BH formation channels in both timescale and impact on the explosion. We simulate these events self-consistently from core-collapse until $20\text{-}50$ days after collapse using three axisymmetric models of a $60$ M$_\odot$ zero-age main sequence progenitor star and investigate how the composition of the ejecta is impacted by the BH formation. We employ Skyrme-type equations of state (EOSs) and vary the uncertain nucleonic effective mass, which affects the pressure inside the proto-neutron star through the thermal part of the EOS. This results in different BH formation times and explosion energies at BH formation, yielding final explosion energies between $0.06\text{-}0.72\times 10^{51}$ erg with $21.8\text{-}23.3$ M$_\odot$ of ejecta, of which $0\text{-}0.018$ M$_\odot$ is $^{56}$Ni. Compared to expectations from 1D simulations, we find a more nuanced EOS dependence of the explosion dynamics, the mass of the BH remnant, and the elemental composition of the ejecta. We investigate why the explosions survive despite the massive overburden and link the shape of the diagnostic energy curve and character of the ejecta evolution to the progenitor structure.

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arXiv2024

Data-driven core collapse supernova multilateration with first neutrino events

A Galactic core-collapse supernova (CCSN) is likely to be observed in neutrino detectors around the world minutes to hours before the electromagnetic radiation arrives. The SNEWS2.0 network of neutrino and dark matter detectors aims to use the relative arrival times of the neutrinos at the different experiments to point back to the supernova so as to facilitate follow-up observation. One of the simplest methods to estimate the CCSN direction is to use the first neutrino events detected through the inverse beta decay (IBD) process, $\overline{\nu}_e p\rightarrow e^+n$. We will consider neutrino detectors sensitive to IBD interactions with low backgrounds. The difference in signal arrival times between a large and a small detector will be biased, however, with the first event at the smaller detector, on average, arriving later than that at the larger detector. This bias can be mitigated by using these first events in a data-driven approach without recourse to simulations or models. The resulting method requires, at minimum, only the times of the first events at most detectors, along with a longer time series of events from one larger detector to act as a reference lightcurve. In this article, we demonstrate this method and its uncertainty estimate using pairs of detectors of different sizes and with different supernova distances. Finally, we use this method to calculate probability skymaps using four detectors currently in operation (Super-Kamiokande, JUNO, LVD, and SNO+) and show that the calculated probabilities yield appropriate confidence intervals for all supernova directions. The area of the 68\% confidence interval varies by distance and direction, but is expected to be a few thousand square degrees. The resulting skymaps should be useful for the multi-messenger community as a rapid, initial pointing to follow up on the SNEWS2.0 Galactic CCSN neutrino alert.

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arXiv2023

Impact of Rotation on the Multimessenger Signatures of a Hadron-quark Phase Transition in Core-collapse Supernovae

We study the impact of rotation on the multimessenger signals of core-collapse supernovae (CCSNe) with the occurrence of a first-order hadron-quark phase transition (HQPT). We simulate CCSNe with the \texttt{FLASH} code starting from a 20~$M_\odot$ progenitor with different rotation rates, and using the RDF equation of state from \textit{Bastian} 2021 that prescribes the HQPT. Rotation is found to delay the onset of the HQPT and the resulting dynamical collapse of the protocompact star (PCS) due to the centrifugal support. All models with the HQPT experience a second bounce shock which leads to a successful explosion. The oblate PCS as deformed by rotation gives rise to strong gravitational-wave (GW) emission around the second bounce with a peak amplitude larger by a factor of $\sim10$ than that around the first bounce. The breakout of the second bounce shock at the neutrinosphere produces a $\barν_e$-rich neutrino burst with a luminosity of serveral 10$^{53}$~erg~s$^{-1}$. In rapidly rotating models the PCS pulsation following the second bounce generates oscillations in the neutrino signal after the burst. In the fastest rotating model with the HQPT, a clear correlation is found between the oscillations in the GW and neutrino signals immediately after the second bounce. In addition, the HQPT-induced collapse leads to a jump in the ratio of rotational kinetic energy to gravitational energy ($β$) of the PCS, for which persistent GW emission may arise due to secular nonaxisymmetric instabilities.

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arXiv2022

Neutrino Driven Explosions aided by Axion Cooling in Multidimensional Simulations of Core-Collapse Supernovae

In this study, we present the first multidimensional core-collapse supernovae (CCSNe) simulations including QCD axions in order to assess the impact on the CCSN explosion mechanism. We include axions in our simulations through the nucleon-nucleon bremsstrahlung emission channel and as a pure energy-sink term under the assumption that the axions free-stream after being emitted. We perform both spherically symmetric (1D) and axisymmetric (2D) simulations. In 1D, we utilize a parameterized heating scheme to achieve explosions, whereas in 2D we self-consistently realize explosions through the neutrino heating mechanism. Our 2D results for a $20 M_\odot$ progenitor show an impact of the axion emission on the shock behavior and the explosion time when considering values of the Peccei-Quinn energy scale $f_a \leq 2 \times 10^8$ GeV. The strong cooling due to the axion emission accelerates the contraction of the core and leads to more efficient neutrino heating and earlier explosions. For the axion emission formalism utilized, the values of $f_a$ that impact the explosion are close to, but in tension with current limits based on the neutrinos detected from SN1987A. However, given the non-linear behavior of the emission and the multidimensional nature of CCSNe, we suggest that a self-consistent, multidimensional approach to simulating CCSNe, including any late time accretion and cooling, is needed to fully explore the axion bounds from supernovae and the impact on the CCSN explosion mechanism.

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arXiv2021

Neutrino Echos following Black Hole Formation in Core-Collapse Supernovae

During a failed core-collapse supernova, the protoneutron star eventually collapses under its own gravitational field and forms a black hole. This collapse happens quickly, on the dynamical time of the protoneutron star, $\lesssim$0.5 ms. During this collapse, barring any excessive rotation, the entire protoneutron star is accreted into the newly formed black hole. The main source of neutrinos is now removed and the signal abruptly shuts off over this formation timescale. However, while the source of neutrinos is turned off, the arrival times at an Earth-based detector will depend on the neutrino path. We show here that a modest amount of neutrinos, emitted just prior to the black hole forming, scatter on the infalling material into our line of sight and arrive after the formation of the black hole, up to 15 ms in our model. This neutrino echo, which we characterize with Monte Carlo simulations and analytic models, has a significantly higher average energy (upwards of $\sim$ 50 MeV) compared to the main neutrino signal, and for the canonical failed supernova explored here, is likely detectable in $\mathcal{O}$(10 kT) supernova neutrino detectors for Galactic failed supernovae. The presence of this signal is important to consider if using black hole formation as a time post for triangulation or the post black hole timing profile for neutrino mass measurements. On its own, it can also be used to characterize or constrain the structure and nature of the accretion flow.

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arXiv2021

SNEWPY: A Data Pipeline from Supernova Simulations to Neutrino Signals

Current neutrino detectors will observe hundreds to thousands of neutrinos from a Galactic supernovae, and future detectors will increase this yield by an order of magnitude or more. With such a data set comes the potential for a huge increase in our understanding of the explosions of massive stars, nuclear physics under extreme conditions, and the properties of the neutrino. However, there is currently a large gap between supernova simulations and the corresponding signals in neutrino detectors, which will make any comparison between theory and observation very difficult. SNEWPY is an open-source software package which bridges this gap. The SNEWPY code can interface with supernova simulation data to generate from the model either a time series of neutrino spectral fluences at Earth, or the total time-integrated spectral fluence. Data from several hundred simulations of core-collapse, thermonuclear, and pair-instability supernovae is included in the package. This output may then be used by an event generator such as sntools or an event rate calculator such as SNOwGLoBES. Additional routines in the SNEWPY package automate the processing of the generated data through the SNOwGLoBES software and collate its output into the observable channels of each detector. In this paper we describe the contents of the package, the physics behind SNEWPY, the organization of the code, and provide examples of how to make use of its capabilities.

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arXiv2021

Calibration of the Advanced Spectral Leakage scheme for neutron star merger simulations, and extension to smoothed-particle hydrodynamics

We calibrate a neutrino transport approximation, called Advanced Spectral Leakage (ASL), with the purpose of modeling neutrino-driven winds in neutron star mergers. Based on a number of snapshots we gauge the ASL parameters by comparing against both the two-moment (M1) scheme implemented in the FLASH code and the Monte Carlo neutrino code Sedonu. The ASL scheme contains three parameters, the least robust of which results to be a blocking parameter for electron neutrinos and anti-neutrinos. The parameter steering the angular distribution of neutrino heating is re-calibrated compared to the earlier work. We also present a new, fast and mesh-free algorithm for calculating spectral optical depths, which, when using Smoothed Particle Hydrodynamics (SPH), makes the neutrino transport completely particle-based. We estimate a speed-up of a factor of 100 in the optical depth calculation when comparing to a grid-based approach. In the suggested calibration we recover luminosities and mean energies within 25%. A comparison of the rates of change of internal energy and electron fraction in the neutrino-driven wind suggests comparable accuracies of ASL and M1, but a higher computational efficiency of the ASL scheme. We estimate that the ratio between the CPU hours spent on the ASL neutrino scheme and those spent on the hydrodynamics is 0.8 per timestep when considering the SPH code MAGMA2 as source code for the Lagrangian hydrodynamics, to be compared with a factor of 10 from the M1 in FLASH.

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arXiv2021

General Relativistic Neutrino-Driven Turbulence in One-Dimensional Core-Collapse Supernovae

Convection and turbulence in core-collapse supernovae (CCSNe) are inherently three-dimensional in nature. However, 3D simulations of CCSNe are computationally demanding. Thus, it is valuable to modify simulations in spherical symmetry to incorporate 3D effects using some parametric model. In this paper, we report on the formulation and implementation of general relativistic (GR) neutrino-driven turbulent convection in the spherically symmetric core-collapse supernova code \texttt{GR1D}. This is based upon the recently proposed method of Supernova Turbulence in Reduced-dimensionality (\textit{STIR}) in Newtonian simulations from \cite{Couch2020_STIR}. When the parameters of this model are calibrated to 3D simulations, we find that our GR formulation of \textit{STIR} requires larger turbulent eddies to achieve a shock evolution similar to the original \textit{STIR} model. We also find that general relativity may alter the correspondence between progenitor mass and successful vs.~failed explosions.

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arXiv2021

Measuring the distance and mass of galactic core-collapse supernovae using neutrinos

Neutrinos from a Galactic core-collapse supernova will be measured by neutrino detectors minutes to days before an optical signal reaches Earth. We present a novel calculation showing the ability of current and near-future neutrino detectors to make fast predictions of the progenitor distance and place constraints on the zero-age main sequence mass in order to inform the observing strategy for electromagnetic follow-up. We show that for typical Galactic supernovae, the distance can be constrained with an uncertainty of $\sim$5\% using IceCube or Hyper-K and, furthermore, the zero-age main sequence mass can be constrained for extremal values of compactness.

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arXiv2020

Impact of neutrino pair-production rates in Core-Collapse Supernovae

In this paper, we present a careful study on the impact of neutrino pair-production on core-collapse supernovae via spherically-symmetric, general-relativistic simulations of two different massive star progenitors with energy-dependent neutrino transport. We explore the impact and consequences of both the underlying microphysics and the implementation in the radiation transport algorithms on the supernova evolution, neutrino signal properties, and the explosion dynamics. We consider the two dominant neutrino pair-production processes found in supernovae, electron-positron annihilation as well as nucleon-nucleon bremsstrahlung in combination with both a simplified and a complete treatment of the processes in the radiation transport algorithms. We find that the use of the simplified prescription quantitatively impacts the neutrino signal at the 10\% level and potentially the supernova dynamics, as we show for the case of a 9.6M$_\odot$ progenitor. We also show that the choice of nucleon-nucleon bremsstrahlung interaction can also have a quantitative impact on the neutrino signal. A self-consistent treatment with state-of-the-art microphysics is suggested for precision simulations of core collapse, however the simplified treatment explored here is both computationally less demanding and results in a qualitatively similar evolution.

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arXiv2019

Multimessenger Asteroseismology of Core-Collapse Supernovae

We investigate correlated gravitational wave and neutrino signals from rotating core-collapse supernovae with simulations. Using an improved mode identification procedure based on mode function matching, we show that a linear quadrupolar mode of the core produces a dual imprint on gravitational waves and neutrinos in the early post-bounce phase of the supernova. The angular harmonics of the neutrino emission are consistent with the mode energy around the neutrinospheres, which points to a mechanism for the imprint on neutrinos. Thus, neutrinos carry information about the mode amplitude in the outer region of the core, whereas gravitational waves probe deeper in. We also find that the best-fit mode function has a frequency bounded above by $\sim 420$ Hz, and yet the mode's frequency in our simulations is $\sim 15\%$ higher, due to the use of Newtonian hydrodynamics and a widely used pseudo-Newtonian gravity approximation. This overestimation is particularly important for the analysis of gravitational wave detectability and asteroseismology, pointing to limitations of pseudo-Newtonian approaches for these purposes, possibly even resulting in excitation of incorrect modes. In addition, mode frequency matching (as opposed to mode function matching) could be resulting in mode misidentification in recent work. Lastly, we evaluate the prospects of a multimessenger detection of the mode using current technology. The detection of the imprint on neutrinos is most challenging, with a maximum detection distance of $\sim\!1$ kpc using the IceCube Neutrino Observatory. The maximum distance for detecting the complementary gravitational wave imprint is $\sim\!5$ kpc using Advanced LIGO at design sensitivity.

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arXiv2019

A multi-dimensional implementation of the Advanced Spectral neutrino Leakage scheme

We present a new, multi-dimensional implementation of the Advanced Spectral Leakage (ASL) scheme with the purpose of modelling neutrino-matter interactions in neutron star mergers. A major challenge is the neutrino absorption in the semi-transparent regime, which is responsible for driving winds from the merger remnant. The composition of such winds is crucial in the understanding of the electromagnetic emission in the recently observed macronova following GW170817. Compared to the original version, we introduce an optical-depth-dependent flux factor to model the average angle of neutrino propagation, and a modulation that accounts for flux anisotropies in non-spherical geometries. We scrutinise our approach by first comparing the new scheme against the original one for a spherically symmetric core-collapse supernova snapshot, both in 1D and in 3D, and additionally against a two-moment (M1) scheme as implemented in 1D into the code GR1D. The luminosities and mean energies agree to a few percents in most tests. Finally, for the case of a binary merger remnant snapshot we compare the new ASL scheme with the M1 scheme that is implemented in the Eulerian adaptive mesh refinement code FLASH. We find that the neutrino absorption distribution in the semi-transparent regime is overall well reproduced. Both approaches agree to within $\lesssim 15\%$ for the average energies and to better than $\sim 35 \%$ in the total luminosities.

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arXiv2019

Evolution of the progenitors of SNe 1993J and 2011dh revealed through late time radio and X-ray studies

We perform hydrodynamical simulations of the interaction between supernova (SN) ejecta and circumstellar medium (CSM) for SN 1993J and SN 2011dh, and calculate the radio and X-ray emissions expected from the shocked gas at late epochs ($t$). Considering the ejecta structure from multi-group radiation hydrodynamics simulation, we find that the observed rapid drop in radio and X-ray light curves of SN 1993J at $t>$3000 days can be due to a change in the mass-loss rate ($\dot M$) around $\sim$6500 years prior to the explosion of the SN. The exact epoch scales inversely with the assumed wind velocity of $v_{\rm w}=10~ km~s^{-1}$. The progenitor of this SN very likely belonged to a binary system, where, during its evolution, the primary had transferred material to the secondary. It is argued in the paper that the change in $\dot M$ can happen because of a change in the mass accretion efficiency ($η$) of the companion star. It is possible that before $\sim6500~(v_{\rm w}/10~km~s^{-1})^{-1}$years prior to the explosion, $η$ was high, thus the CSM was tenuous, which causes the late time downturn in fluxes. In the case of SN 2011dh, the late time evolution is found to be consistent with a wind medium with $\dot M/v_{\rm w}=4\times10^{-6 }~M_{\odot}~ yr^{-1}/10 ~{km ~s^{-1}}$. It is difficult from our analysis to predict whether the progenitor of this SN had a binary companion, however, if future observations show similar decrease in radio and X-ray fluxes, then that would give strong support to a scenario where both SNe had undergone similar kind of binary evolution before explosion.

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arXiv2018

FRIB and the GW170817 Kilonova

In July 2018 an FRIB Theory Alliance program was held on the implications of GW170817 and its associated kilonova for r-process nucleosynthesis. Topics of discussion included the astrophysical and nuclear physics uncertainties in the interpretation of the GW170817 kilonova, what we can learn about the astrophysical site or sites of the r process from this event, and the advances in nuclear experiment and theory most crucial to pursue in light of the new data. Here we compile a selection of scientific contributions to the workshop, broadly representative of progress in r-process studies since the GW170817 event.

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