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  • 1. Brege, Wyatt
    et al.
    Duez, Matthew D.
    Foucart, Francois
    Deaton, M. Brett
    Caro, Jesus
    Hemberger, Daniel A.
    Kidder, Lawrence E.
    O'Connor, Evan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Pfeiffer, Harald P.
    Scheel, Mark A.
    Black hole-neutron star mergers using a survey of finite-temperature equations of state2018In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 98, no 6, article id 063009Article in journal (Refereed)
    Abstract [en]

    Each of the potential signals from a black hole-neutron star merger should contain an imprint of the neutron star equation of state: gravitational waves via its effect on tidal disruption, the kilonova via its effect on the ejecta, and the gamma-ray burst via its effect on the remnant disk. These effects have been studied by numerical simulations and quantified by semianalytic formulas. However, most of the simulations on which these formulas are based use equations of state without finite temperature and composition-dependent nuclear physics. In this paper, we simulate black hole-neutron star mergers varying both the neutron star mass and the equation of state, using three finite-temperature nuclear models of varying stiffness. Our simulations largely vindicate formulas for ejecta properties but do not find the expected dependence of disk mass on neutron star compaction. We track the early evolution of the accretion disk, largely driven by shocking and fallback inflow, and do find notable equation-of-state effects on the structure of this early-time, neutrino-bright disk.

  • 2. Deaton, M. Brett
    et al.
    O'Connor, Evan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). North Carolina State University, USA.
    Zhu, Y. L.
    Bohn, Andy
    Jesse, Jerred
    Foucart, Francois
    Duez, Matthew D.
    McLaughlin, G. C.
    Elastic scattering in general relativistic ray tracing for neutrinos2018In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 98, no 10, article id 103014Article in journal (Refereed)
    Abstract [en]

    We present a covariant ray tracing algorithm for computing high-resolution neutrino distributions in general relativistic numerical spacetimes with hydrodynamical sources. Our formulation treats the very important effect of elastic scattering of neutrinos off of nuclei and nucleons (changing the neutrino's direction but not energy) by incorporating estimates of the background neutrino fields. Background fields provide information about the spectra and intensities of the neutrinos scattered into each ray. These background fields may be taken from a low-order moment simulation or be ignored, in which case the method reduces to a standard state-of-the-art ray tracing formulation. The method handles radiation in regimes spanning optically thick to optically thin. We test the new code, highlight its strengths and weaknesses, and apply it to a simulation of a neutron-star merger to compute neutrino fluxes and spectra, and to demonstrate a neutrino flavor oscillation calculation. In that environment, we find qualitatively different fluxes, spectra, and oscillation behaviors when elastic scattering is included.

  • 3.
    Kundu, Esha
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sorokina, E.
    Pérez-Torres, M. A.
    Blinnikov, S.
    O'Connor, Evan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Chandra, Poonam
    Stockholm University, Faculty of Science, Department of Astronomy. Pune University, Sweden.
    Das, B.
    uEvolution of the Progenitors of SNe 1993J and 2011dh Revealed through Late-time Radio and X-Ray Studies2019In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 875, no 1, article id 17Article in journal (Refereed)
    Abstract [en]

    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 may be due to a change in the mass-loss rate ((M)over dot) similar to 6500 yr prior to the explosion of the SN. The exact epoch scales inversely with the assumed wind velocity of nu(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 this paper that the change in (M)over dot can happen because of a change in the mass accretion efficiency (eta) of the companion star. It is possible that before similar to 6500. (nu(w)/10 km s(-1))(-1) yr prior to the explosion, eta was high, and 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 (M)over dot/nu(w) = 4 x 10(-6) M-circle dot 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 a similar decrease in radio and X-ray fluxes, then this would give strong support to a scenario where both SNe had undergone a similar kind of binary evolution before explosion.

  • 4.
    O'Connor, Evan
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). North Carolina State University, United States of America.
    Boilig, Robert
    Burrows, Adam
    Couch, Sean
    Fischer, Tobias
    Janka, Hans-Thomas
    Kotake, Kei
    Lentz, Eric J.
    Liebendörfer, Matthias
    Messer, O. E. Bronson
    Mezzacappa, Anthony
    Takiwaki, Tomoya
    Vartanyan, David
    Global comparison of core-collapse supernova simulations in spherical symmetry2018In: Journal of Physics G: Nuclear and Particle Physics, ISSN 0954-3899, E-ISSN 1361-6471, Vol. 45, no 10, article id 104001Article in journal (Refereed)
    Abstract [en]

    We present a comparison between several simulation codes designed to study the core-collapse supernova mechanism. We pay close attention to controlling the initial conditions and input physics in order to ensure a meaningful and informative comparison. Our goal is three-fold. First, we aim to demonstrate the current level of agreement between various groups studying the corecollapse supernova central engine. Second, we desire to form a strong basis for future simulation codes and methods to compare to. Lastly, we want this work to be a stepping stone for future work exploring more complex simulations of core-collapse supernovae, i.e., simulations in multiple dimensions and simulations with modern neutrino and nuclear physics. We compare the early (first similar to 500 ms after core bounce) spherically-symmetric evolution of a 20 M-circle dot progenitor star from six different core-collapse supernovae codes: 3DnSNeIDS A, AGILE-BOLTZTRAN, FLASH, FORNAX, GR1D, and PROMETHEUS-VERTEX. Given the diversity of neutrino transport and hydrodynamic methods employed, we find excellent agreement in many critical quantities, including the shock radius evolution and the amount of neutrino heating. Our results provide an excellent starting point from which to extend this comparison to higher dimensions and compare the development of hydrodynamic instabilities that are crucial to the supernova explosion mechanism, such as turbulence and convection.

  • 5.
    O'Connor, Evan P.
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Couch, Sean M.
    Exploring Fundamentally Three-dimensional Phenomena in High-fidelity Simulations of Core-collapse Supernovae2018In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 865, no 2, article id 81Article in journal (Refereed)
    Abstract [en]

    The details of the physical mechanism that drives core-collapse supernovae (CCSNe) remain uncertain. While there is an emerging consensus on the qualitative outcome of detailed CCSN mechanism simulations in 2D, only recently have high-fidelity 3D simulations become possible. Here we present the results of an extensive set of 3D CCSN simulations using high-fidelity multidimensional neutrino transport, high-resolution hydrodynamics, and approximate general relativistic gravity. We employ a state-of-the-art 20 M-circle dot progenitor generated using Modules for Experiments in Stellar Astrophysics, and the SFHo equation of state. While none of our 3D CCSN simulations explode within similar to 500 ms after core bounce, we find that the presence of large-scale aspherical motion in the Si and O shells aid shock expansion and bring the models closer to the threshold of explosion. We also find some dependence on resolution and geometry (octant versus full 4 pi). As has been noted in other recent works, we find that the post-shock turbulence plays an important role in determining the overall dynamical evolution of our simulations. We find a strong standing accretion shock instability (SASI) that develops at late times. The SASI produces transient shock expansions, but these do not result in any explosions. We also report that for a subset of our simulations, we find conclusive evidence for the lepton-number emission self-sustained asymmetry, which until now has not been confirmed by independent simulation codes. Both the progenitor asphericities and the SASI-induced transient shock expansion phases generate transient gravitational waves and neutrino signal modulations via perturbations of the protoneutron star by turbulent motions.

  • 6.
    O'Connor, Evan P.
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). North Carolina State University, USA.
    Couch, Sean M.
    Two-dimensional Core-collapse Supernova Explosions Aided by General Relativity with Multidimensional Neutrino Transport2018In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 854, no 1, article id 63Article in journal (Refereed)
    Abstract [en]

    We present results from simulations of core-collapse supernovae in FLASH using a newly implemented multidimensional neutrino transport scheme and a newly implemented general relativistic (GR) treatment of gravity. We use a two-moment method with an analytic closure (so-called M1 transport) for the neutrino transport. This transport is multienergy, multispecies, velocity dependent, and truly multidimensional, i.e., we do not assume the commonly used ray-by-ray approximation. Our GR gravity is implemented in our Newtonian hydrodynamics simulations via an effective relativistic potential that closely reproduces the GR structure of neutron stars and has been shown to match GR simulations of core collapse quite well. In axisymmetry, we simulate core-collapse supernovae with four different progenitor models in both Newtonian and GR gravity. We find that the more compact proto-neutron star structure realized in simulations with GR gravity gives higher neutrino luminosities and higher neutrino energies. These differences in turn give higher neutrino heating rates (upward of similar to 20%-30% over the corresponding Newtonian gravity simulations) that increase the efficacy of the neutrino mechanism. Three of the four models successfully explode in the simulations assuming GREP gravity. In our Newtonian gravity simulations, two of the four models explode, but at times much later than observed in our GR gravity simulations. Our results, in both Newtonian and GR gravity, compare well with several other studies in the literature. These results conclusively show that the approximation of Newtonian gravity for simulating the core-collapse supernova central engine is not acceptable. We also simulate four additional models in GR gravity to highlight the growing disparity between parameterized 1D models of core-collapse supernovae and the current generation of 2D models.

  • 7. Pajkos, Michael A.
    et al.
    Couch, Sean M.
    Pan, Kuo-Chuan
    O'Connor, Evan P.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Features of Accretion-phase Gravitational-wave Emission from Two-dimensional Rotating Core-collapse Supernovae2019In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 878, no 1, article id 13Article in journal (Refereed)
    Abstract [en]

    We explore the influence of progenitor mass and rotation on the gravitational-wave (GW) emission from core-collapse supernovae, during the postbounce, preexplosion, accretion phase. We present the results from 15 two-dimensional (2D) neutrino radiation-hydrodynamic simulations from initial stellar collapse to similar to 300 ms after core bounce. We examine the features of the GW signals for four zero-age main sequence (ZAMS) progenitor masses ranging from 12 M-circle dot to 60 M-circle dot and four core rotation rates from 0 to 3 rad s(-1). We find that GW strain immediately around core bounce is fairly independent of ZAMS mass and-consistent with previous findings-that it is more heavily dependent on the core angular momentum. At later times, all nonrotating progenitors exhibit loud GW emission, which we attribute to vibrational g-modes of the protoneutron star (PNS) excited by convection in the postshock layer and the standing accretion shock instability (SASI). We find that increasing rotation rates results in muting of the accretion-phase GW signal due to centrifugal effects that inhibit convection in the postshock region, quench the SASI, and slow the rate at which the PNS peak vibrational frequency increases. Additionally, we verify the efficacy of our approximate general relativistic (GR) effective potential treatment of gravity by comparing our core bounce GW strains with the recent 2D GR results of other groups.

  • 8. Pan, Kuo-Chuan
    et al.
    Mattes, Carlos
    O'Connor, Evan P.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Couch, Sean M.
    Perego, Albino
    Arcones, Almudena
    The impact of different neutrino transport methods on multidimensional core-collapse supernova simulations2019In: Journal of Physics G: Nuclear and Particle Physics, ISSN 0954-3899, E-ISSN 1361-6471, Vol. 46, no 1, article id 014001Article in journal (Refereed)
    Abstract [en]

    Neutrinos play a crucial role in the core-collapse supernova (CCSN) explosion mechanism. The requirement of accurately calculating the transport of neutrinos makes simulations of the CCSN mechanism extremely challenging and computationally expensive. Historically, this stiff challenge has been met by making approximations to the full transport equation. In this work, we compare CCSN simulations in one- and two-dimensions with three approximate neutrino transport schemes, each implemented in the FLASH simulation framework. We compare a two-moment M1 scheme with an analytic closure (M1), the isotropic diffusion source approximation (IDSA), and the advanced spectral leakage method. We identify and discuss the advantages and disadvantages of each scheme. For each approximate transport scheme, we use identical grid setups, hydrodynamics, and gravity solvers to investigate the transport effects on supernova shock dynamics and neutrino quantities. We find that the transport scheme has a small effect on the evolution of protoneutron star (PNS) radius, PNS mass, and the mass accretion rate. The neutrino luminosities, mean energies, and shock radii have a -10%-20% quantitative difference but the overall qualitative trends are fairly consistent between all three approximations. We find larger differences in the gain region properties, including the gain region mass and the net heating rate in the gain region, as well as the strength of PNS convection in the core. We investigate the progenitor, nuclear equation of state, and stochastic perturbation dependence of our simulations and find similar magnitudes of impact on key quantities. We also compare the computational expense of the various approximations.

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