Neutrino-driven supernova explosions powered by nuclear reactions

We have investigated the revival of a shock wave by nuclear burning reactions at the central region of core-collapse supernovae. For this purpose, we performed hydrodynamic simulations of core collapse and bounce for 15 M ⊙ progenitor model, using ZEUS-MP code in axi-symmetric coordinates. Our numerical code is equipped with a simple nuclear reaction network including 13 α nuclei form 4He to 56Ni, and accounting for energy feedback from nuclear reactions as well as neutrino heating and cooling. We found that the energy released by nuclear reactions is significantly helpful in accelerating shock waves and is able to produce energetic explosion even if the input neutrino luminosity is lo

The Core-Collapse Supernova with "Non-Uniform" Magnetic Fields

We perform two-dimensional numerical simulations on the core-collapse of a massive star with strong magnetic fields and differential rotations using a numerical code ZEUS-2D. Changing field configurations and laws of differential rotation parametrically, we compute 14 models and investigate effects of these parameters on the dynamics. In our models, we do not solve the neutrino transport and instead employ a phenomenological parametric EOS that takes into account the neutrino emissions. As a result of the calculations, we find that the field configuration plays a significant role in the dynamics of the core if the initial magnetic field is large enough. Models with initially concentrated fields produce more energetic explosions and more prolate shock waves than the uniform field. Quadrapole-like fields produce remarkably collimated and fast jet, which might be important for gamma-ray bursts(GRB). The Lorentz forces exerted in the region where the plasma-beta is less than unity are responsible for these dynamics. The pure toroidal field, on the other hand, does not lead to any explosion or matter ejection. This suggests the presupernova models of Heger et al.(2003), in which toroidal fields are predominant, is disadvantageous for the magnetorotation-induced supernova considered here. Models with initially weak magnetic fields do not lead to explosion or matter ejection, either. In these models magnetic fields play no role as they do not grow on the timescale considered in this paper so that the magnetic pressure could be comparable to the matter pressure. This is because the exponential field growth as expected in MRI is not seen in our models. The magnetic field is amplified mainly by field-compression and field-wrapping in our simulations.Comment: 24 pages, 5 figures, ApJ in press, typos correcte

Magnetohydrodynamic Simulations of A Rotating Massive Star Collapsing to A Black Hole

We perform two-dimensional, axisymmetric, magnetohydrodynamic simulations of the collapse of a rotating star of 40 Msun and in the light of the collapsar model of gamma-ray burst. Considering two distributions of angular momentum, up to \sim 10^{17} cm^2/s, and the uniform vertical magnetic field, we investigate the formation of an accretion disk around a black hole and the jet production near the hole. After material reaches to the black hole with the high angular momentum, the disk is formed inside a surface of weak shock. The disk becomes in a quasi-steady state for stars whose magnetic field is less than 10^{10} G before the collapse. We find that the jet can be driven by the magnetic fields even if the central core does not rotate as rapidly as previously assumed and outer layers of the star has sufficiently high angular momentum. The magnetic fields are chiefly amplified inside the disk due to the compression and the wrapping of the field. The fields inside the disk propagate to the polar region along the inner boundary near the black hole through the Alfv{\'e}n wave, and eventually drive the jet. The quasi-steady disk is not an advection-dominated disk but a neutrino cooling-dominated one. Mass accretion rates in the disks are greater than 0.01 Msun/sec with large fluctuations. The disk is transparent for neutrinos. The dense part of the disk, which locates near the hole, emits neutrino efficiently at a constant rate of < 8 \times 10^{51} erg/s. The neutrino luminosity is much smaller than those from supernovae after the neutrino burst.Comment: 42 pages, accepted for publication in the Astrophysical Journal. A paper with higher-resolution figures available at http://www.ec.knct.ac.jp/~fujimoto/collapsar/mhd-color.pd

Gravitational Waves from Core Collapse Supernovae

We present the gravitational wave signatures for a suite of axisymmetric core collapse supernova models with progenitors masses between 12 and 25 solar masses. These models are distinguished by the fact they explode and contain essential physics (in particular, multi-frequency neutrino transport and general relativity) needed for a more realistic description. Thus, we are able to compute complete waveforms (i.e., through explosion) based on non-parameterized, first-principles models. This is essential if the waveform amplitudes and time scales are to be computed more precisely. Fourier decomposition shows that the gravitational wave signals we predict should be observable by AdvLIGO across the range of progenitors considered here. The fundamental limitation of these models is in their imposition of axisymmetry. Further progress will require counterpart three-dimensional models.Comment: 10 pages, 5 figure

North-South Neutrino Heating Asymmetry in Strongly Magnetized and Rotating Stellar Cores

We perform a series of two-dimensional magnetohydrodynamic simulations of supernova cores. Since the distributions of the angular momentum and the magnetic fields of strongly magnetized stars are quite uncertain, we systematically change the combinations of the strength of the angular momentum, the rotations law, the degree of differential rotation, and the profiles of the magnetic fields to construct the initial conditions. By so doing, we estimate how the rotation-induced anisotropic neutrino heating are affected by the strong magnetic fields through parity-violating effects and first investigate how the north-south asymmetry of the neutrino heating in a strongly magnetized supernova core could be. As for the microphysics, we employ a realistic equation of state based on the relativistic mean field theory and take into account electron captures and the neutrino transport via the neutrino leakage scheme. With these computations, we find that the parity-violating corrections reduce $\lesssim 0.5$ of the neutrino heating rate than that without the magnetic fields in the vicinity of the north pole of a star, on the other hand, enhance about $\lesssim 0.5$ in the vicinity of the south pole. If the global asymmetry of the neutrino heating in the both of the poles develops in the later phases, the newly born neutron star might be kicked toward the north pole in the subsequent time.Comment: 25 pages, 6 figures, ApJ in press. A paper with higher-resolution figures available at http://www-utap.phys.s.u-tokyo.ac.jp/~kkotake/lonbun.htm

Long non-coding RNA ANRIL is required for the PRC2 recruitment to and silencing of p15INK4Btumor suppressor gene

A 42 kb region on human chromosome 9p21 encodes for three distinct tumor suppressors, p16INK4A, p14ARF and p15INK4B, and is altered in an estimated 30–40% of human tumors. The expression of the INK4A-ARF-INK4B gene cluster is silenced by polycomb during normal cell growth and is activated by oncogenic insults and during aging. How the polycomb is recruited to repress this gene cluster is unclear. Here, we show that expression of oncogenic Ras, which stimulates the expression of p15INK4B and p16INK4A, but not p14ARF, inhibits the expression of ANRIL (antisense non-coding RNA in the INK4 locus), a 3.8 kb-long non-coding RNA expressed in the opposite direction from INK4A-ARF-INK4B. We show that the p15INK4B locus is bound by SUZ12, a component of polycomb repression complex 2 (PRC2), and is H3K27-trimethylated. Notably, depletion of ANRIL disrupts the SUZ12 binding to the p15INK4B locus, increases the expression of p15INK4B, but not p16INK4A or p14ARF, and inhibits cellular proliferation. Finally, RNA immunoprecipitation demonstrates that ANRIL binds to SUZ12 in vivo. Collectively, these results suggest a model in which ANRIL binds to and recruits PRC2 to repress the expression of p15INK4B locus