Andrzej Odrzywolek

Detection possibility of the pair-annihilation neutrinos from the neutrino-cooled pre-supernova star

Abstract The signal produced in neutrino observatories by the pair-annihilation neutrinos emitted from a 20 M⊙ pre-supernova star at the silicon burning phase is estimated. The spectrum of the neutrinos with an average energy ∼2 MeV is calculated with the use of the Monte Carlo method. A few relevant reactions for neutrinos and anti-neutrinos in modern detectors are considered. The most promising results are from ν e + p → n + e + reaction. During the Si-burning phase we expect 1.27 neutrons/day/kton of water to be produced by neutrinos from a star located at a distance of 1 kpc. Small admixture of effective neutron-absorbers as e.g. NaCl or GdCl3 makes these neutrons easily visible because of Cherenkov light produced by electrons which were hit by ∼8 MeV photon cascade emitted by Cl or Gd nuclei. The estimated rate of neutron production for SNO and Super-Kamiokande is, respectively, 2.2 and 41 events per day for a star at 1 kpc. For future detectors UNO and Hyper-Kamiokande we expect 5.6 and 6.9 events per day even for a star 10 kpc away. This would make it possible to foresee a massive star death a few days before its core collapse. Importance of such a detection for theoretical astrophysics is discussed.

Holes in the static Einstein universe and a model of the cosmological voids

A spherically symmetric, static model of the cosmological voids is constructed in the framework of the Tolman-Oppenheimer-Volkov equation with the cosmological constant. Extension of the Tooper result (dimensionless form of the TOV equation) is provided for nonzero {lambda}. Then, the equation is simplified in {alpha}{yields}0, {lambda}{yields}0, and {lambda}/{alpha}=const regime, suitable for largest structures in {lambda}-dominated universe. Voids are treated as underdensity regions in the static Einstein universe. Both overdensity and underdensity (relative to static universe) solutions exist. They are identified with standard astrophysical spherical objects and voids, respectively. The model is tested against observed properties (the radius - the central density relation) and density profiles of voids. Analytical formulas for radial density contrast profile and radii of the voids are derived. Some consequences for cosmological N-body simulations are suggested. Hints on the dark matter/dark energy EOS filling the voids are provided.

Neutrino spectrum from the pair-annihilation process in the hot stellar plasma

A new method of calculating the energy spectrum of neutrinos and antineutrinos produced in the electron-positron annihilation processes in hot stellar plasma is presented. Detection of these neutrinos, produced copiously in the presupernova, which is an evolutionary advanced neutrino-cooled star, may serve in the future as a trigger of a precollapse early warning system. Also, observation of neutrinos will probe final stages of thermonuclear burning in the presupernova. The spectra obtained with the new method are compared to Monte Carlo simulations. To achieve high accuracy in the energy range of interest, determined by neutrino detector thresholds, a differential cross section for production of the antineutrino, previously unknown in an explicit form, is calculated as a function of energy in the plasma rest frame. The neutrino spectrum is obtained as a 3-dimensional integral, computed with the use of the Cuhre algorithm of at least 5% accuracy. Formulas for the mean neutrino energy and its dispersion are given as a combination of Fermi-Dirac integrals. Also, useful analytical approximations of the whole spectrum are shown.

Probing thermonuclear supernova explosions with neutrinos

Aims. We present neutrino light curves and energy spectra for two representative type Ia supernova explosion models: a pure deflagration and a delayed detonation. Methods. We calculate the neutrino flux from β processes using nuclear statistical equilibrium abundances convoluted with approximate neutrino spectra of the individual nuclei and the thermal neutrino spectrum (pair+plasma). Results. Although the two considered thermonuclear supernova explosion scenarios are expected to produce almost identical electromagnetic output, their neutrino signatures appear vastly different, which allows an unambiguous identification of the explosion mechanism: a pure deflagration produces a single peak in the neutrino light curve, while the addition of the second maximum characterizes a delayed-detonation. We identified the following main contributors to the neutrino signal: (1) weak electron neutrino emission from electron captures (in particular on the protons 55 Co and 56 Ni) and numerous β-active nuclei produced by the thermonuclear flame and/or detonation front, (2) electron antineutrinos from positron captures on neutrons, and (3) the thermal emission from pair annihilation. We estimate that a pure deflagration supernova explosion at a distance of 1 kpc would trigger about 14 events in the future 50 kt liquid scintillator detector and some 19 events in a 0.5 Mt water Cherenkov-type detector. Conclusions. While in contrast to core-collapse supernovae neutrinos carry only a very small fraction of the energy produced in the thermonuclear supernova explosion, the SN Ia neutrino signal provides information that allows us to unambiguously distinguish between different possible explosion scenarios. These studies will become feasible with the next generation of proposed neutrino observatories.

Nuclear statistical equilibrium neutrino spectrum

The spectral emission of neutrinos from a plasma in nuclear statistical equilibrium (NSE) is investigated. Particular attention is paid to the possible emission of high-energy (>10 MeV) neutrinos or antineutrinos. A newly developed numerical approach for describing the abundances of nuclei in NSE is presented. Neutrino emission spectra, resulting from general Fuller-Fowler-Newman conditions, are analyzed. Regions of T-{rho}-Y{sub e} space favoring detectability are selected. The importance of critical Y{sub e} values with zero net rate of neutronization (Y{sub e}) is discussed. Results are provided for the processing of matter under conditions typical for thermonuclear and core-collapse supernovae, presupernova stars, and neutron star mergers.

Analytical approximation for the structure of differentially rotating barotropes

The approximate analytical formula for density distribution in differentially rotating stars is derived. Any barotropic equation of state and conservative rotation law can be handled by using this method for a wide range of differential rotation strengths. The results are in good qualitative agreement in comparison to other methods. Some applications are suggested and possible improvements of the formula are discussed.

Gaussian integration with rescaling of abscissas and weights

Abstract An algorithm for integration of the polynomial functions with a variable weight is considered. It provides an extension of the Gaussian integration, with appropriate scaling of the abscissas and weights. In a first step, orthogonal polynomials are computed for a fixed a = 1 . Then, using approximate scaling, the initial guess is constructed for a ≠ 1 . Finally, numerical values of the abscissas and weights are refined, solving polynomial system using Newton–Raphson method. The final form of the algorithm provides good alternative to usually adopted interval splitting, automatically avoiding problems with limiting values of parameter present in the weight function. Construction of the method requires arbitrary precision arithmetic and special functions, polylogarithms in particular. The final form of the algorithm can be coded using machine precision floating point numbers and standard mathematical library.

Future neutrino observations of nearby pre‐supernova stars before core‐collapse

We discuss important issues which are essential for understanding future capabilities of the large water Cherenkov detectors from astrophysical point of view. The paper is concentrated on the detection of the neutrinos, which are emitted before core‐collapse from massive stars.

NSE abundance data

Abstract A novel method of calculating nuclear statistical equilibrium (NSE) is presented. Basic equations are carefully solved using arbitrary precision arithmetic. A special interpolation procedure is then used to retrieve all abundances using tabulated results for neutrons and protons, together with basic nuclear data. Proton and neutron abundance tables, basic nuclear data, and partition functions for nuclides used in the calculations are provided. A simple interpolation algorithm using pre-calculated p and n abundances tabulated as functions of k T , ρ and Y e is outlined. Unique properties of this method are: (1) ability to pick up out of NSE selected nuclei only, (2) computational time scaling linearly with number of re-calculated abundances, (3) relatively small amount of stored data: only two large tables, (4) slightly faster than solving the NSE equations using traditional Newton–Raphson methods for small networks (few tens of species); superior for huge (800–3000) networks, (5) does not require initial guess; works well on random input, (6) can be tailored to specific application, (7) ability to use third-party NSE solvers to obtain fully compatible tables, and (8) encapsulation of the NSE code for bug-free calculations. A range of applications for this approach is possible: covering tests of traditional NSE Newton–Raphson codes, generating starting values, code-to-code verification, and possible replacement of the old legacy procedures in supernova simulations.

Thermal neutrinos from pre-supernova

We would like to discuss prospects for neutrino observations of the core-collapse supernova progenitor during neutrino-cooled stage. We will present new theoretical results on thermal neutrino and antineutrino spectra produced deep inside the pre-supernova core. Three competing processes: pair-, photo and plasma-neutrino production, are taken into account. The results will be used to estimate signal in existing and future neutrino detectors. Chance for supernova prediction is estimated, with possible aid to core-collapse neutrino and gravitational wave detectors in the form of early warning.