Supernova neutrinos and antineutrinos: ternary luminosity diagram and spectral split patterns

In core-collapse supernovae, the nu_e and anti-nu_e species may experience collective flavor swaps to non-electron species nu_x, within energy intervals limited by relatively sharp boundaries ("splits"). These phenomena appear to depend sensitively upon the initial energy spectra and luminosities. We investigate the effect of generic variations of the fractional luminosities (l_e, l_{anti-e}, l_x) with respect to the usual "energy equipartition" case (1/6, 1/6, 1/6), within an early-time supernova scenario with fixed thermal spectra and total luminosity. We represent the constraint l_e+l_{anti-e}+4l_x=1 in a ternary diagram, which is explored via numerical experiments (in single-angle approximation) over an evenly-spaced grid of points. In inverted hierarchy, single splits arise in most cases, but an abrupt transition to double splits is observed for a few points surrounding the equipartition one. In normal hierarchy, collective effects turn out to be unobservable at all grid points but one, where single splits occur. Admissible deviations from equipartition may thus induce dramatic changes in the shape of supernova (anti)neutrino spectra. The observed patterns are interpreted in terms of initial flavor polarization vectors (defining boundaries for the single/double split transitions), lepton number conservation, and minimization of potential energy.Comment: 24 pages, including 14 figures (1 section with 2 figures added). Accepted for publication in JCA

The late time radio emission from SN 1993J at meter wavelengths

We present the investigations of SN 1993J using low frequency observations with the Giant Meterwave Radio Telescope. We analyze the light curves of SN 1993J at 1420, 610, 325 and 243 MHz during $7.5-10$ years since explosion.The supernova has become optically thin early on in the 1420 MHz and 610 MHz bands while it has only recently entered the optically thin phase in the 325 MHz band. The radio light curve in the 235 MHz band is more or less flat. This indicates that the supernova is undergoing a transition from an optically thick to optically thin limit in this frequency band. In addition, we analyze the SN radio spectra at five epochs on day 3000, 3200, 3266, 3460 and 3730 since explosion. Day 3200 spectrum shows a synchrotron cooling break. SN 1993J is the only young supernova for which the magnetic field and the size of the radio emitting region are determined through unrelated methods. Thus the mechanism that controls the evolution of the radio spectra can be identified. We suggest that at all epochs, the synchrotron self absorption mechanism is primarily responsible for the turn-over in the spectra. Light curve models based on free free absorption in homogeneous or inhomogeneous media at high frequencies overpredict the flux densities at low frequencies. The discrepancy is increasingly larger at lower and lower frequencies. We suggest that an extra opacity, sensitively dependent on frequency, is likely to account for the difference at lower frequencies. The evolution of the magnetic field (determined from synchrotron self absorption turn-over) is roughly consistent with $B \propto t^{-1}$. Radio spectral index in the optically thin part evolves from $\alpha \sim 0.8-1.0$ at few tens of days to $\sim 0.6$ in about 10 years.Comment: 37 pages, 9 figures in LaTex; scheduled for ApJ 10 September 2004, v612 issue; send comments to: [email protected]

Mass-density relationship in molecular cloud clumps

We study the mass-density relationship n ~ m^x in molecular cloud condensations (clumps), considering various equipartition relations between their gravitational, kinetic, internal and magnetic energies. Clumps are described statistically, with a density distribution that reflects a lognormal probability density function (pdf) in turbulent cold interstellar medium. The clump mass-density exponent $x$ derived at different scales $L$ varies in most of the cases within the range $-2.5\lesssim x \lesssim-0.2$, with a pronounced scale dependence and in consistency with observations. When derived from the global size-mass relationship m ~ l^{\gamma_{glob}} for set of clumps, generated at all scales, the clump mass-density exponent has typical values $-3.0\lesssim x(\gamma_{glob}) \lesssim -0.3$ that depend on the forms of energy, included in the equipartition relations and on the velocity scaling law whereas the description of clump geometry is important when magnetic energy is taken into account.Comment: Accepted in MNRAS, 14 pages, 8 figure

Dynamical Friction from field particles with a mass spectrum

The analytical generalization of the classical dynamical friction formula (derived under the assumption that all the field particles have the same mass) to the case in which the masses of the field particles are distributed with a mass spectrum is presented. Two extreme cases are considered: in the first, energy equipartition is assumed, in the second all the field particles have the same (Maxwellian) velocity distribution. Three different mass spectra are studied in detail, namely the exponential, discrete (two components), and power-law cases. It is found that the dynamical friction deceleration can be significantly stronger than in the equivalent classical case, with the largest differences (up to a factor of 10 or more in extreme cases) arising for test particle velocities comparable to the mass-averaged velocity dispersion of the field particles. The present results are relevant to our understanding of the dynamical evolution of globular clusters, in particular in the modelization of mass segregation and sedimentation of Blue Straggler stars and Neutron stars, and for the study of binary black holes in galactic nuclei.Comment: 12 pages, 3 figures, proceedings of the international symposium "Plasmas in the laboratory and in the universe: interactions, patterns, and turbulence", Como 1-4 Dec. 2009, eds. G. Bertin et al., AIP Conf. Se

Thermodynamic evolution of cosmological baryonic gas: I. Influence of non-equipartition processes

Using N-body/hydrodynamic simulations, the influence of non-equipartition processes on the thermal and dynamical properties of cosmological baryonic gas is investigated. We focus on a possible departure from equilibrium between electrons, ions and neutral atoms in low temperature (10^4-10^6 K) and weakly ionized regions of the intergalactic medium. The simulations compute the energy exchanges between ions, neutrals and electrons, without assuming thermal equilibrium. They include gravitation, shock heating and cooling processes, and follow self-consistently the chemical evolution of a primordial composition hydrogen-helium plasma without assuming collisional ionization equilibrium. At high redshift, a significant fraction of the intergalactic medium is found to be warmer and weakly ionized in simulations with non-equipartition processes than in simulations in which the cosmological plasma is considered to be in thermodynamic equilibrium. With a semi-analytical study of the out of equilibrium regions we show that, during the formation of cosmic structures, departure from equilibrium in accreted plasma results from the competition between the atomic cooling processes and the elastic processes between heavy particles and electrons. Our numerical results are in agreement with this semi-analytical model. Therefore, since baryonic matter with temperatures around 10^4 K is a reservoir for galaxy formation, non-equipartition processes are expected to modify the properties of the objects formed.Comment: 15 pages, 16 figures. Accepted for publication in A&A. For a version with high-resolution figures, see http://www.raunvis.hi.is/~courty/series.htm