Evan O'Connor



Stockholm University
Albanova University Center
Department of Astronomy SE-106 91 Stockholm, Sweden
CV

Open-source Tools

NuLib
GR1D
EOS Routines


I am a Biträdande lektor (Assistant Professor) in the Astronomy Department at Stockholm University. I am mainly interested in the dynamics of compact objects via their creation in supernovae and their connection to the detailed microphysics. I am also particularly interesting the associated neutrino signal and what its measurement can tell us about the underlying microphysics. I graduated with my Ph.D. from Caltech in the TAPIR group, my advisor was Christian Ott. If you are interested, here is my thesis. I obtained my bachelor from the University of Prince Edward Island (UPEI) in 2007 in Science (Physics, Honours, Co-op). I was a postdoctoral fellow at the Canadian Institute of Astrophysics from 2012-2014 and a Hubble Fellow in the Physics Department at North Carolina State University from 2014-2017. For all the details, have a look below and/or at my CV. Here is my author query at arXiv, and my article library at Nasa ADS.

Profiled Work


Two Dimensional Core-Collapse Supernova Explosions Aided by General Relativity with Multidimensional Neutrino Transport, E. O'Connor, S. Couch, submitted to ApJ 2015 , arXiv link

Shock radius evolution for five core-collapse supernova simulations using general relativistic gravity and a two moment neutrino transport, both new additions to the FLASH core-collapse code. Three of the five GR simulations are successful and develop explosions within 300-700 ms after bounce.

    

In in paper we introduce two new improvements to the core-collapse supernova simulation package that is built on the FLASH hydrodynamics code. We implement a general relativistic effective potential into our Newtonian hydrodynamics simulations. This allows us to capture the proper general relativistic structure of the PNS in the core-collapse supernova central engine. We also implement a truly multidimensional, energy-dependent, multispecies, two moment neutrino transport scheme with an analytic closure (so-called M1). With these improvements, we perform simulations of five progenitors using both Newtonian and general relativistic treatments of gravity. Interestingly, we find explosions (in three of five models) only when using general relativistic gravity. Furthermore, our results compare well to other simulations in the literature!

An Open-Source Neutrino Radiation Hydrodynamics Code for Core-Collapse Supernovae, E. O'Connor, ApJS 219 24 2015, ApJS link arXiv link

Comparison of the central lepton fractions and central entropy of GR1Dv2 compared to full Boltzmann transport solutions from Liebendoerfer et al. (2005). GR1Dv2 performs equally well comparing radial profiles at and after bounce, as well as when comparing the neutrino signals (luminosities, root mean squared energies).

    

In this article, I develop and make open-source a new neutrino radiation hydrodynamic code designed for core-collpase supernovae. Additionally, I present NuLib, an open-source neutrino interaction library. GR1Dv2 and Nulib can simulate the core collapse, bounce, and postbounce phases of a core-collapse supernovae and obtain results that compare well to Boltzmann transport calculations. The routines are specifically designed to work well with multidimensional transport codes as excellent results can be obtained without the need to invert any matrix larger than the number of dimensions plus 1. This transport code is fully general relativistic, can handle inelastic scattering interactions, pair-production interactions, neutrino energy couplings, and full velocity dependence of the transport equations. Besides a detailed comparison to Boltzmann transport results, we test our code on the evolution of a failed core-collapse supernovae up to black hole formation.

The Progenitor Dependence of the Preexplosion Neutrino Emission in Core-Collapse Supernovae, E. O'Connor and C.D. Ott ApJ 762 126 ApJ link, arXiv link

Neutrino luminosities and average energies for 32 progenitor models. The color corresponds to the compactness of the progenitor star at the time of bounce. Low compactness progenitors have small postbounce accretion rates and low postbounce luminosities. Higher compactness progenitors have larger accretion rates and larger luminosities. The temperature in the postshock region also increases with compactness of the progenitor models, this leads to a systematic increase in the average energies with compactness.


In this paper, Christian and I implement a new neutrino transport scheme into GR1D. It is a two moment closure scheme based on the truncated moment formalism of Shibata et al. (2011) and Audit et al. (2002). We evolve 32 progenitor stars from Woosley and Heger (2007) with two equations of state and study the progenitor dependence of the preexplosion neutrino spectra. We show that the emitted neutrino luminosities and spectra follow very systematic trends that are correlated with the compactness (~M/R) of the progenitor star's inner regions via the accretion rate in the preexplosion phase. We find that these qualitative trends depend only weakly on the nuclear equation of state, but quantitative observational statements will require independent constraints on the equation of state and the rotation rate of the core as well as a more complete understanding of neutrino oscillations. We investigate the simulated response of water Cherenkov detectors to the electron antineutrino fluxes from our models and find that the large statistics of a galactic core collapse event may allow robust conclusions on the inner structure of the progenitor star.

The Role of Collective Neutrino Flavor Oscillations in Core-Collapse Supernova Shock Revival, B. Dasgupta, E. O'Connor, C. D. Ott PRD 85 065008 (2012). PRD link, arXiv link

Evolution of the average, north pole and south pole values of the shock radius versus time for a 2D core-collapse supernova simulation with VULCAN/2D. Also shown is the expected radius (both numerical and analytic predictions) at which collective neutrino oscillations begin and end. We find little room for collective neutrino oscillations to enhance neutrino heating. See description to the left, or, even better, read the paper!

    

The neutrino mechanism for Core-Collapse Supernova shock revival most likely plays a large role in exploding garden-variety massive stars. However, in one and possibly two dimensions, the robustness of this mechanism has not been demonstrated. We still do not know the details of how massive stars explode. Collective neutrino oscillations (CNO) are a mechanism, in addition to standard vacuum and matter oscillations, through which neutrinos can oscillate between flavor states. CNOs occur when the density of neutrinos is sufficiently high to influence the evolution of the neutrino fields. Neutrino densities of this order are reached only in the early universe and in the core of a protoneutron star formed in a core-collapse supernova. If collective neutrino oscillations occur soon after the core of a massive star collapses it may be possible for the more energetic mu and tau neutrinos to oscillate into electron type neutrino and enhance the efficiency of the neutrino mechanism. Our simulations show that the neutrinos emitted in the first 100s of milliseconds after bounce do not start to oscillate until a radius where they will not contribute to the neutrino mechanism :(

Black Hole Formation in Failing Core-Collapse Supernovae, E. O'Connor and C. D. Ott, Astrophys. J. 730 70 (2011) ApJ link, arXiv link

Outcome of core collapse (either explosion or failed supernova) for single, nonrotating, massive stars for moderately stiff equations of state. We find that neutrino driven explosions are likely to fail for values of the bounce compactness > 0.45. Low metallicity stars likely form black holes for ZAMS masses greater than ~30 solar masses, ~15% for a Salpeter IMF. For solar metallicity stars the percentage is less and strongly depends on the mass loss perscription, but can be as high as 7%. For full details, read the paper!

    

In this large systematic study of failing core-collapse supernova, Christian and I study the dependence of black hole formation on ZAMS mass and metallicity, mass loss prescription, nuclear EOS, and rotation. We make use of GR1D, our open-source, spherically symmetric, general-relativistic hydrodynamics code along with simplified neutrino physics that allows us to perform over 700 simulations. One of the main results of this project is the prediction of what progenitor stars lead to a failed supernova. This is depicted in the figure to the left.

A New Open-Source Code for Spherically-Symmetric Stellar Collapse to Neutron Stars and Black Holes, E. O'Connor and C. D. Ott, Class. Quan. Grav. 27, 114103 (2010). CQG link, arXiv link

Shown is the shock radius (maroon) and the neutrino luminosity for electron neutrinos and antineutrinos as well as a representative neutrino encompassing all 4 \mu and \tau neutrinos and antineutrinos. The difference between the solid maroon and dashed hot pink line shows the effect of neutrino heating in the post shock region.

    

This paper is result of a long project developing an open-source, spherically-symmetric, general-relativistic Eulerian hydrodynamic code used to study core collapse, proto-neutron star formation and early evolution as well as black hole formation. It is work done in close collaboration with Christian Ott. The code is called GR1D and is available at stellarcollapse.org. It includes multiple finite-temperature EOS (also available at stellarcollapse.org), a 3-flavour neutrino leakage and heating scheme and effective 1D rotation. We are using GR1D to study black hole formation in stellar collapse but GR1D can quickly be adapted to study many areas of core collapse and proto-neutron star evolution. If you are interested please download and use GR1D, and we are open to collaboration if you have a idea you want to pursue with us. Shown on the left is a typical simulation with GR1D, This shows the postbounce evolution of a 40 solar mass progenitor taken from Woosley & Weaver (1995). It uses GR1D's standard core collapse settings and the Lattimer & Swesty K=180 MeV EOS.

Influence of light nuclei on neutrino-driven supernova outflows, A. Arcones, G. Martinez-Pinedo, E. O'Connor, A. Schwenk, H.-Th. Janka, C. J. Horowitz, and K. Langanke, Phys. Rev. C 78, 015806 (2008). PRC link, arXiv link

Mass fraction of A=1,2,3,4 nuclei (and a representative heavy nucleus for NSE EOS) as a function of radius. The solid lines denote the location of the neutrinosphere (inner = antineutrino, outer = neutrino). Lines are marked by species and show the mass fraction for (a) dashed - standard supernova EOS (b) dotted - NSE EOS and (c) solid - virial EOS. Note the divergence on the proton and 4He nuclei mass fractions at low radii.

In this work we looked at how the composition of the neutrinosphere in a supernova is effected by the inclusion of light nuclei, i.e. deuterons, tritons, and 3He nuclei in addition to the usual suspects in the neutrinosphere: neutrons, protons and 4He nuclei. In addition to studying the effect on the composition, we looked at light nuclei's effect on the emitted neutrino spectrum. As expected, the neutrino spectrum is not significantly effected as neutrinos interact mainly with neutrons; neutrons are not dramatically effected by light nuclei. We find however that the emitted anti-neutrino spectrum is effected, for example, the post-bounce antineutrino spectrum's average energy is reduced by ~1 MeV. The neutrino and anti-neutrino spectrum emitted from the neutrinosphere are not only interesting for detection purposes but they are also interesting because these neutrinos and anti-neutrinos are important in nucleosynthesis further out in the recently exploded star.

Neutrino Breakup of A=3 Nuclei in Supernovae, E. O'Connor, D Gazit, C. J. Horowitz, A. Schwenk, and N. Barnea, Phys. Rev. C 75, 055803 (2007). PRC link, arXiv link

Neutrino energy loss due to inelastic excitations (breakup) of A=3,4 nuclei. dotted (red) is 4He nucleus contribution to the energy loss, dash-dot-dot (blue) is triton particle contribution and dash-dash-dot (green) is for 3He nucleus. The solid line (black) to the sum of all three contributions. The three graphs show different proton fractions.

In this paper we first introduced A=3 nuclei to the low-density virial expansion EOS. While 4He nuclei are typically more abundant, the binding energy is large compared to neutrino energies and also large compared to A=3 binding energies, therefore inelastic energy transfer cross sections of neutrinos on A=3 nuclei is important to consider in addition to the corresponding cross section of 4He nuclei. This paper also details the calculation of the inelastic cross sections through ab-initio methods.


A series of snapshots during collapse (left t=0, middle t=83 ps, right t=680ps).

Unrelated to astrophysics, my undergraduate thesis, under the supervision of Sheldon Opps at UPEI, involved discontinuous molecular dynamics (DMD). A copy can be found here. In this thesis project we explored simple computational models of Langmuir monolayers. A Langmuir monolayer is a collection of surfactant molecules on the surface of water. These layers are one molecule thick (hence monolayer) and are arranged so that the hydrophilic (water liking) part of the molecule is at the water-layer boundary and the hydrophobic (water fearing) part of the molecule, typically a carbon chain, is pointed out of the water. A common example of a surfactant molecule is stearic acid. Of particular interest in this thesis was the mechanisms and dynamics of monolayer collapse.

Publications


Equation of state effects on gravitational waves from rotating core collapse, Richers, S., Ott, C. D., Abdikamalov, E.,O'Connor, E., Sullivan, C., PRD 95 063019 2017 PRD link arXiv link
Neutrino-nucleon scattering in supernova matter from the virial expansion, Horowitz, C. J., Caballero, O. L., Lin, Z., O'Connor, E., Schwenk, A., PRC 95 025801 2017 PRC link arXiv link
Impact of an improved neutrino energy estimate on outflows in neutron star merger simulations, Foucart, F., O'Connor, E.; Roberts, L., Kidder, L. E., Pfeiffer, H. P., Scheel, M. A., PRD 94 123016 PRD link arXiv link
Nuclear pasta and supernova neutrinos at late times, Horowitz, C. J., Berry, D. K., Caplan, M. E., Fischer, T., Lin, Z., Newton, W. G., O'Connor, E., Roberts, L. F., submitted to PRL arXiv link
General-Relativistic Three-Dimensional Multi-group Neutrino Radiation-Hydrodynamics Simulations of Core-Collapse Supernovae, Roberts, L. F., Ott, C. D., Haas, R.; O'Connor, E., Diener, P., Schnetter, E., ApJ link arXiv link
Unequal mass binary neutron star mergers and multimessenger signals, Lehner, L., Liebling, S. L., Palenzuela, C., Caballero, O. L., O'Connor, E, Anderson, M., Neilsen, D., CQG 33 184002 2016 CQG link arXiv link
Ankowski et al., White paper on Supernova Physics at DUNE arXiv link
Two Dimensional Core-Collapse Supernova Explosions Aided by General Relativity with Multidimensional Neutrino Transport, O'Connor, E., Couch, S. submitted to ApJ 2015 arXiv link
Low mass binary neutron star mergers: gravitational waves and neutrino emission, Foucart, F., Haas, R., Duez, M. D., O'Connor, E., Ott, C. D., Roberts, L., Kidder, L. E., Lippuner, J., Pfeiffer, H. P., Scheel, M. A., PRD 93 044019 PRD link arXiv link
The Sensitivity of Core-Collapse Supernovae to Nuclear Electron Capture, Sullivan, C., O'Connor, E., Zegers, R. G. T., Grubb, T., Austin, S. M., ApJ 816 44 2016 ApJ link arXiv link
Monte Carlo Neutrino Transport Through Remnant Disks from Neutron Star Mergers, Richers, S., Kasen, D., O'Connor, E., Fernandez, R., Ott, C.D., ApJ 813 38 2015 ApJ link arXiv link
Effects of the microphysical Equation of State in the mergers of magnetized Neutron Stars With Neutrino Cooling, Palenzuela, C., Liebling, S. L., Neilsen, D., Lehner, L., Caballero, O. L., O'Connor, E. Anderson, M., PRD 92 044045 2015 PRD link arXiv link
An Open-Source Neutrino Radiation Hydrodynamics Code for Core-Collapse Supernovae, O'Connor, E. ApJS 219 24 2015 ApJS link arXiv link
Post-merger evolution of a neutron star-black hole binary with neutrino transport, Foucart, F., O'Connor, E, Roberts, L., Duez, M.D., Haas, R., Kidder, L.E., Ott, C.D. Pfeiffer, H.P., Scheel, M.A., Szilagyi, B., PRD 91 124021 2015 PRD Link arXiv link
Magnetized neutron stars with realistic equations of state and neutrino cooling, Neilsen, D., Liebling, S.L., Anderson, M., Lehner, L., O'Connor, E. Palenzuela, C., PRD 89 104029 2014 PRD link arXiv link
Neutron star-black hole mergers with a nuclear equation of state and neutrino cooling: Dependence in the binary parameters, Foucart, F., Deaton, M. B., Duez, M. D., O'Connor, E., Ott, C. D., Haas, R., Kidder, L. E., Pfeiffer, H. P., Scheel, M. A., Szilagyi, B. PRD 90 024026 2014 PRD Link arXiv link
High-Resolution Three-Dimensional Simulations of Core-Collapse Supernovae in Multiple Progenitors, Couch, S. M., O'Connor, E., ApJ 785 123 2014 ApJ link arXiv link
The Influence of Thermal Pressure on Hypermassive Neutron Star Merger Remnants, Kaplan, J. D., Ott, C. D., O'Connor, E., Kiuchi, K., Roberts, L., Duez, M. ApJ 790 19 2014 ApJ Link arXiv link
Black Hole-Neutron Star Mergers with a Hot Nuclear Equation of State: Outflow and Neutrino-Cooled Disk for a Low-Mass, High-Spin Case, Deaton, M. B., Duez, M. D., Foucart, F., O'Connor, E., Ott, C. D., Kidder, L. E., Muhlberger, C. D., Scheel, M. A., Szilagyi, B. ApJ 776 47 (2013) ApJ link arXiv link
General-Relativistic Simulations of Three-Dimensional Core-Collapse Supernovae, Ott, C.D., Abdikamalov, E., Moesta, P., Haas, R., Drasco, S., O'Connor, E., Reisswig, C., Meakin, C., Schnetter, E. ApJ 768 115 (2013), ApJ link arXiv link
The Progenitor Dependence of the Preexplosion Neutrino Emission in Core-Collapse Supernovae, O'Connor, E. and Ott, C.D. ApJ 762 126 (2013), ApJ link arXiv link
Charged current neutrino interactions in core-collapse supernovae in a virial expansion, Horowitz, C.J., Shen, G., O'Connor, E., C.D. Ott PRC 86 065806 (2012) PRC link arXiv link
Correlated Gravitational Wave and Neutrino Signals from General-Relativistic Rapidly Rotating Iron Core Collapse, Ott, C.D., Abdikamalov, E., O'Connor, E., Reisswig, C., Haas, R., Kalmus, P., Drasco, S., Burrows, A., Schnetter, E. PRD 86 024026 (2012), arXiv link PRD link
A New Monte Carlo Method for Time-Dependent Neutrino Radiation Transport, Abdikamalov, E., Burrows, A., Ott, C.D., Loeffler, F., O'Connor, E., Dolence, J., Schnetter, E. ApJ 755 111 (2012), arXiv link ApJ link
The Arduous Journey to Black-Hole Formation in Potential Gamma-Ray Burst Progenitors, Dessart, L., O'Connor, E., Ott, C.D. ApJ 754 76 (2012), ApJ link arXiv link
The Role of Collective Neutrino Flavor Oscillations in Core-Collapse Supernova Shock Revival, Dasgupta, B., O'Connor, E., Ott, C.D. PRD 85 065008 (2012). PRD link, arXiv link
A Second Relativistic Mean Field and Virial Equation of State for Astrophysical Simulations, Shen, G., Horowitz, C.J., O'Connor, E., PRC 83 065808 (2011). PRC link, arXiv link
Black Hole Formation in Failing Core-Collapse Supernovae, O'Connor, E. and Ott, C.D. ApJ 730 70 (2011). ApJ link, arXiv link
Dynamics and Gravitational Wave Signature of Collapsar Formation, Ott, C.D., Reisswig, C., Schnetter, E., O'Connor, E., Sperhake, U., Loeffler, F., Diener, P., Abdikamalov, E., Hawke, I. and Burrows, A. PRL 106 161103 2011, PRL link, arXiv link
A New Open-Source Code for Spherically-Symmetric Stellar Collapse to Neutron Stars and Black Holes, O'Connor, E. and Ott, C.D., Class. Quan. Grav. 27, 114103 (2010). CQG link, arXiv link
Influence of light nuclei on neutrino-driven supernova outflows, Arcones, A., Martinez-Pinedo, G., O'Connor, E., Schwenk, A., Janka, H.Th., Horowitz, C.J., and Langanke, K., Phys. Rev. C 78, 015806 (2008). PRC link, arXiv link
Neutrino Breakup of A=3 Nuclei in Supernovae, O'Connor, E., Gazit, D., Horowitz, C.J., Schwenk, A., and Barnea, N., Phys. Rev. C 75, 055803 (2007). PRC link, arXiv link
Measurement of the 40Ca(α,γ)44Ti reaction relevant for supernova nucleosynthesis, Vockenhuber, C., Ouellet, C. O., The, L.-S., Buchmann, L., Caggiano, J., Chen, A. A., Crawford, H., D'Auria, J. M., Davids, B., Fogarty, L., Frekers, D., Hussein, A., Hutcheon, D. A., Kutschera, W., Laird, A. M., Lewis, R., O'Connor, E., Ottewell, D., Paul, M., Pavan, M. M., Pearson, J., Ruiz, C., Ruprecht, G., Trinczek, M., Wales, B., Wallner, A., Phys. Rev. C 76, 035801 (2007). PRC link
Charge-state distributions after radiative capture of helium nuclei by a carbon beam, Zylberberg, J., Hutcheon, D., Buchmann, L., Caggiano, J., Hannes, W. R., Hussein, A., O'Connor, E., Ottewell, D., Pearson, J., Ruiz, C., Ruprecht, G., Trinczek, M. and Vockenhuber, C. , NIM-B 254, 17 (2007). Science Direct link
Radio emission models of colliding-wind binary systems. Inclusion of IC cooling., Pittard, J. M., Dougherty, S. M., Coker, R. F., O'Connor, E., Bolingbroke, N. J., Astron. and Astrophys. 446, 1001 (2006). Astronomy and Astrophysics link, arXiv link
May, 2017