Search for surviving companions in type Ia supernova remnants

The nature of the progenitor systems of type~Ia supernovae is still unclear. One way to distinguish between the single-degenerate scenario and double-degenerate scenario for their progenitors is to search for the surviving companions. Using a technique that couples the results from multi-dimensional hydrodynamics simulations with calculations of the structure and evolution of main-sequence- and helium-rich surviving companions, the color and magnitude of main-sequence- and helium-rich surviving companions are predicted as functions of time. The surviving companion candidates in Galactic type~Ia supernova remnants and nearby extragalactic type~Ia supernova remnants are discussed. We find that the maximum detectable distance of main-sequence surviving companions (helium-rich surviving companions) is $0.6-4$~Mpc ($0.4-16$~Mpc), if the apparent magnitude limit is 27 in the absence of extinction, suggesting that the Large and Small Magellanic Clouds and the Andromeda Galaxy are excellent environments in which to search for surviving companions. However, only five Ia~SNRs have been searched for surviving companions, showing little support for the standard channels in the singe-degenerate scenario. To better understand the progenitors of type Ia supernovae, we encourage the search for surviving companions in other nearby type Ia supernova remnants.Comment: 25 pages, 5 figures, and 2 tables. Accepted for publication in Ap

Simulations of the symbiotic recurrent nova V407 Cyg. I. Accretion and shock evolutions

The shock interaction and evolution of nova ejecta with a wind from a red giant star in a symbiotic binary system are investigated via three-dimensional hydrodynamics simulations. We specifically model the March 2010 outburst of the symbiotic recurrent nova V407~Cygni from the quiescent phase to its eruption phase. The circumstellar density enhancement due to wind-white dwarf interaction is studied in detail. It is found that the density-enhancement efficiency depends on the ratio of the orbital speed to the red giant wind speed. Unlike another recurrent nova, RS~Ophiuchi, we do not observe a strong disk-like density enhancement, but instead observe an aspherical density distribution with $\sim 20\%$ higher density in the equatorial plane than at the poles. To model the 2010 outburst, we consider several physical parameters, including the red giant mass loss rate, nova eruption energy, and ejecta mass. A detailed study of the shock interaction and evolution reveals that the interaction of shocks with the red giant wind generates strong Rayleigh-Taylor instabilities. In addition, the presence of the companion and circumstellar density enhancement greatly alter the shock evolution during the nova phase. The ejecta speed after sweeping out most of the circumstellar medium decreases to $\sim 100-300$ km-s$^{-1}$, depending on model, which is consistent with the observed extended redward emission in [N~II] lines in April 2011.Comment: ApJ, In Press. Simulation Animation: https://youtu.be/g5Nu7vDfCO

Multi-dimensional Core-Collapse Supernova Simulations with Neutrino Transport

We present multi-dimensional core-collapse supernova simulations using the Isotropic Diffusion Source Approximation (IDSA) for the neutrino transport and a modified potential for general relativity in two different supernova codes: FLASH and ELEPHANT. Due to the complexity of the core-collapse supernova explosion mechanism, simulations require not only high-performance computers and the exploitation of GPUs, but also sophisticated approximations to capture the essential microphysics. We demonstrate that the IDSA is an elegant and efficient neutrino radiation transfer scheme, which is portable to multiple hydrodynamics codes and fast enough to investigate long-term evolutions in two and three dimensions. Simulations with a 40 solar mass progenitor are presented in both FLASH (1D and 2D) and ELEPHANT (3D) as an extreme test condition. It is found that the black hole formation time is delayed in multiple dimensions and we argue that the strong standing accretion shock instability before black hole formation will lead to strong gravitational waves.Comment: 3 pages, proceedings for Nuclei in the Cosmos XIV, Niigata, Japan (2016

Two-Dimensional Core-Collapse Supernova Simulations with the Isotropic Diffusion Source Approximation for Neutrino Transport

The neutrino mechanism of core-collapse supernova is investigated via non-relativistic, two-dimensional (2D), neutrino radiation-hydrodynamic simulations. For the transport of electron flavor neutrinos, we use the interaction rates defined by Bruenn (1985) and the isotropic diffusion source approximation (IDSA) scheme, which decomposes the transported particles into trapped particle and streaming particle components. Heavy neutrinos are described by a leakage scheme. Unlike the "ray-by-ray" approach in some other multi-dimensional supernova models, we use cylindrical coordinates and solve the trapped particle component in multiple dimensions, improving the proto-neutron star resolution and the neutrino transport in angular and temporal directions. We provide an IDSA verification by performing 1D and 2D simulations with 15 and 20 $M_\odot$ progenitors from Woosley et al.~(2007) and discuss the difference of our IDSA results with those existing in the literature. Additionally, we perform Newtonian 1D and 2D simulations from prebounce core collapse to several hundred milliseconds postbounce with 11, 15, 21, and 27 $M_\odot$ progenitors from Woosley et al.~(2002) with the HS(DD2) equation of state. General relativistic effects are neglected. We obtain robust explosions with diagnostic energies $E_{\rm dig} \gtrsim 0.1- 0.5$~B for all considered 2D models within approximately $100-300$ milliseconds after bounce and find that explosions are mostly dominated by the neutrino-driven convection, although standing accretion shock instabilities are observed as well. We also find that the level of electron deleptonization during collapse dramatically affect the postbounce evolution, e.g.~the ignorance of neutrino-electron scattering during collapse will lead to a stronger explosion.Comment: 23 pages. Accepted for publication in Ap

Evolution of Main-Sequence-like Surviving Companions in Type Ia Supernova Remnants

Recent theoretical and numerical studies of Type Ia supernova explosion within the single-degenerate scenario suggest that the non-degenerate companions could survive during the supernova impact and could be detectable in nearby supernova remnants. However, observational efforts show less promising evidence on the existence of surviving companions from the standard single-degenerate channels. The spin-up/spin-down models are possible mechanisms to explain the non-detection of surviving companions. In these models, the spin-up phase could increase the critical mass for explosion, leading to a super-Chandrasekhar mass explosion, and the spin-down phase could lead to extra mass loss and angular momentum redistribution. Since the spin-down timescale for the delayed explosion of a rotating white dwarf is unclear, in this paper, we explore a vast parameter space of main-sequence-like surviving companions via two-dimensional hydrodynamic simulations of supernova impact and the subsequent stellar evolution of surviving companions. Tight universal relations to describe the mass stripping effect, supernova kick, and depth of supernova heating are provided. Our results suggest that the not-yet detected surviving companions from observations of nearby Type Ia supernova remnants might favor low mass companions, short binary separation, or stronger supernova explosion energies than the standard singe-degenerate channels.Comment: 11 pages, 9 figures. Accepted by Ap

Evolution of MHD Torus and Mass Outflow Around Spinning AGN

We perform axisymmetric, two-dimensional magnetohydrodynamic (MHD) simulations to investigate accretion flows around spinning AGN. To mimic the space-time geometry of spinning black holes, we consider effective Kerr potential, and the mass of the black holes is $10^8 M_{\odot}$. We initialize the accretion disc with a magnetized torus by adopting the toroidal component of the magnetic vector potential. The initial magnetic field strength is set by using the plasma beta parameter ($\beta_0$). We observe self-consistent turbulence generated by magneto rotational instability (MRI) in the disc. The MRI turbulence transports angular momentum in the disc, resulting in an angular momentum distribution that approaches a Keplerian distribution. We investigate the effect of the magnetic field on the dynamics of the torus and associated mass outflow from the disc around a maximally spinning black hole $(a_k = 0.99)$. For the purpose of our analysis, we investigate the magnetic state of our simulation model. The model $\beta_0 = 10$ indicates the behaviour similar to the "magnetically arrested disk (MAD)'' state, and all the other low magnetic model remains in the SANE state. We observe that mass outflow rates are significantly enhanced with the increased magnetic field in the disc. We find a positive correlation between the magnetic field and mass outflow rates. We also investigate the effect of black hole spin on the magnetized torus evolution. However, we have not found any significant effect of black hole spin on mass outflows in our model. Finally, we discuss the possible astrophysical applications of our simulation results.Comment: 15 pages, 13 figures (2 appendix figures), Accepted for publication in MNRA

Stellar Mass Black Hole Formation and Multi-messenger Signals from Three Dimensional Rotating Core-Collapse Supernova Simulations

We present self-consistent, 3D core-collapse supernova simulations of a 40 $M_\odot$ progenitor model using the isotropic diffusion source approximation for neutrino transport and an effective general relativistic potential up to $\sim0.9$~s~postbounce. We consider three different rotational speeds with initial angular velocities of $\Omega_0=0$,~0.5, and~1~rad~s$^{-1}$ and investigate the impact of rotation on shock dynamics, black hole formation, and gravitational wave signals. The rapidly-rotating model undergoes an early explosion at $\sim 250$~ms postbounce and shows signs of the low $T/|W|$ instability. We do not find black hole formation in this model within $\sim 460$~ms postbounce. In contrast, we find black hole formation at 776~ms~postbounce and 936~ms~postbounce for the non-rotating and slowly-rotating models, respectively. The slowly-rotating model explodes at $\sim 650$~ms postbounce and fallback accretion onto the proto-neutron star (PNS) results in BH formation. In addition, the standing~accretion~shock~instability could induce rotation on the proto-neutron star with a non-rotating progenitor and gives a black~hole spin parameter of $a=J/M=0.046$, if the specific angular momentum is conserved during black hole formation. But for the non-rotating model, without an explosion, all the angular momentum should eventually be accreted by the BH, resulting in a non-spinning BH. The successful explosion of the slowly-rotating model drastically slows accretion onto the PNS allowing continued cooling and contraction that results in an extremely high gravitational-wave frequency ($f\sim3000$~Hz) at black~hole formation, while the non-rotating model generates gravitational wave signals similar to its 2D counterpart.Comment: 14 pages, 11 figure

A New Kilohertz Gravitational-Wave Feature from Rapidly Rotating Core-Collapse Supernovae

We present self-consistent three-dimensional core-collapse supernova simulations of a rotating $20M_\odot$ progenitor model with various initial angular velocities from $0.0$ to $4.0$ rad s$^{-1}$ using a smoothed particle hydrodynamics code, SPHYNX, and a grid-based hydrodynamics code, FLASH. We identify two strong gravitational-wave features, with peak frequencies of $\sim300$ Hz and $\sim1.3$ kHz in the first $100$ ms postbounce. We demonstrate that these two features are associated with the $m=1$ deformation from the proto-neutron star (PNS) modulation induced by the low-$T/|W|$ instability, regardless of the simulation code. The $300$ Hz feature is present in models with an initial angular velocity between $1.0$ and $4.0$ rad s$^{-1}$, while the $1.3$ kHz feature is present only in a narrower range, from $1.5$ to $3.5$ rad s$^{-1}$. We show that the $1.3$ kHz signal originates from the high-density inner core of the PNS, and the $m=1$ deformation triggers a strong asymmetric distribution of electron anti-neutrinos. In addition to the $300$ Hz and $1.3$ kHz features, we also observe one weaker but noticeable gravitational-wave feature from higher-order modes in the range between $1.5$ and $3.5$ rad s$^{-1}$. Its peak frequency is around $800$ Hz initially and gradually increases to $900-1000$ Hz. Therefore, in addition to the gravitational bounce signal, the detection of the $300$ Hz, $1.3$ kHz, the higher-order mode, and even the related asymmetric emission of neutrinos, could provide additional diagnostics to estimate the initial angular velocity of a collapsing core.Comment: 20 pages, 14 figures,. Accepted for publication in the Astrophysical Journa