arXiv subjects

L. Zaninetti

Publications and source records attributed to L. Zaninetti.

At least 19 recordsLinked to original sources

arXiv2018

The physics of asymmetric supernovae and supernovae remnants

We model the circumstellar medium with four density profiles: hyperbolic type, power law type, exponential type and Gaussian type. We solve analytically or numerically the four first-order differential equations which arise in the framework of the classical thin layer approximation. The non-cubic dependence of the swept mass with the advancing radius is also considered. We derive the equation of motion for the thin layer approximation in special relativity in two cases. The initial conditions are chosen in order to model the temporal evolution of SN 1987A over 23 years and of SN 1006 over 1000 years. We review the building blocks of the symmetrical and asymmetrical formations of the image.

astro-ph.HE↗

arXiv2017

A left and right truncated lognormal distribution for the stars

The initial mass function for the stars is often modeled by a lognormal distribution. This paper is devoted to demonstrating the advantage of introducing a left and right truncated lognormal probability density function, which is characterized by four parameters. Its normalization constant, mean, the variance, second moment about the origin and distribution function are calculated. The chi-square test and the Kolmogorov--Smirnov test are performed on four samples of stars.

astro-ph.SR↗

arXiv2017

A left and right truncated Schechter luminosity function for quasars

The luminosity function for quasars (QSOs) is usually fitted by a Schechter function. The dependence of the number of quasars on the redshift, both in the low and high luminosity regions, requires the inclusion of a lower and upper boundary in the Schechter function. The normalization of the truncated Schechter function is forced to be the same as that for the Schechter function, and an analytical form for the average value is derived. Three astrophysical applications for QSOs are provided: deduction of the parameters at low redshifts, behavior of the average absolute magnitude at high redshifts, and the location (in redshift) of the photometric maximum as a function of the selected apparent magnitude. The truncated Schechter function with the double power law and an improved Schechter function are compared as luminosity functions for QSOs. The chosen cosmological framework is that of the flat cosmology, for which we provided the luminosity distance, the inverse relation for the luminosity distance, and the distance modulus.

astro-ph.HE↗

arXiv2017

The Ring Produced by an Extra-Galactic Superbubble in Flat Cosmology

A superbubble which advances in a symmetric Navarro--Frenk--White density profile or in an auto-gravitating density profile generates a thick shell with a radius that can reach 10 kpc. The application of the symmetric and asymmetric image theory to this thick 3D shell produces a ring in the 2D map of intensity and a characteristic `U' shape in the case of 1D cut of the intensity. A comparison of such a ring originating from a superbubble is made with the Einstein's ring. A Taylor approximation of order 10 for the angular diameter distance is derived in order to deal with high values of the redshift.

astro-ph.CO↗

arXiv2016

The truncated lognormal distribution as a luminosity function for SWIFT-BAT gamma-ray bursts

The determination of the luminosity function (LF) in gamma ray bursts (GRBs) depends on the adopted cosmology, each one characterized by its corresponding luminosity distance. Here we analyse three cosmologies: the standard cosmology, the plasma cosmology, and the pseudo-Euclidean universe. The LF of the GRBs is firstly modeled by the lognormal distribution and the four broken power law, and secondly by a truncated lognormal distribution. The truncated lognormal distribution fits acceptably the range in luminosity of GRBs as a function of the redshift.

astro-ph.CO↗

arXiv2016

An analytical solution in the complex plane for the luminosity distance in flat cosmology

We present an analytical solution for the luminosity distance in spatially flat cosmology with pressureless matter and the cosmological constant. The complex analytical solution is made of a real part and a negligible imaginary part. The real part of the luminosity distance allows finding the two parameters $H_0$ and $\om$. A simple expression for the distance modulus for SNs of type Ia is reported in the framework of the minimax approximation.

astro-ph.CO↗

arXiv2016

A classical and a relativistic law of motion for SN1987A

In this paper we derive some first order differential equations which model the classical and the relativistic thin layer approximations in the presence of a circumstellar medium with a density which is decreasing in the distance $z$ from the equatorial plane. The circumstellar medium is assumed to follow a density profile with $z$ of hyperbolic type, power law type, exponential type or Gaussian type. The first order differential equations are solved analytically, or numerically, or by a series expansion, or by Padé approximants. The initial conditions are chosen in order to model the temporal evolution of SN 1987A over 23 years. The free parameters of the theory are found by maximizing the observational reliability which is based on an observed section of SN 1987A.

astro-ph.HE↗

arXiv2016

Padé Approximant and Minimax Rational Approximation in Standard Cosmology

The luminosity distance in the standard cosmology as given by $Λ$CDM and consequently the distance modulus for supernovae can be defined by the Padé approximant. A comparison with a known analytical solution shows that the Padé approximant for the luminosity distance has an error of $4\%$ at redshift $= 10$. A similar procedure for the Taylor expansion of the luminosity distance gives an error of $4\%$ at redshift $=0.7 $; this means that for the luminosity distance, the Padé approximation is superior to the Taylor series. The availability of an analytical expression for the distance modulus allows applying the Levenberg--Marquardt method to derive the fundamental parameters from the available compilations for supernovae. A new luminosity function for galaxies derived from the truncated gamma probability density function models the observed luminosity function for galaxies when the observed range in absolute magnitude is modeled by the Padé approximant. A comparison of $Λ$CDM with other cosmologies is done adopting a statistical point of view.

astro-ph.CO↗

arXiv2016

Classical and relativistic flux of energy conservation in astrophysical jets

The conservation of the energy flux in turbulent jets which propagate in the intergalactic medium (IGM) allows deducing the law of motion in the classical and relativistic cases. Three types of IGM are considered: constant density, hyperbolic and inverse power law decrease of density. An analytical law for the evolution of the magnetic field along the radio-jets is deduced using a linear relation between the magnetic pressure and the rest density. Astrophysical applications are made to the centerline intensity of synchrotron emission in NGC315 and to the magnetic field of 3C273.

astro-ph.HE↗

arXiv2015

The Impact Crater Size-Frequency Distribution on Pluto Follows a Truncated Pareto Distribution: Results from a First Data Set Based on the Recent New Horizons' Flyby

Recently it could be shown ( that the impact crater size-frequency distribution of Pluto (based on an analysis of first images obtained by the recent New Horizons flyby) follows a power law alpha = 2.4926 in the interval of diameter (D) values ranging from 3.75 km to the largest determined value of 37.77 km. A reanalysis of this data set revealed that the whole crater SFD (i.e., with values in the interval of 1.2-37.7 km) can be described by a truncated Pareto distribution.

astro-ph.EP↗

arXiv2015

On non-Poissonian Voronoi tessellations

The Voronoi tessellation is the partition of space for a given seeds pattern and the result of the partition depends completely on the type of given pattern "random", Poisson-Voronoi tessellations (PVT), or "non-random", Non Poisson-Voronoi tessellations. In this note we shall consider properties of Voronoi tessellations with centers generated by Sobol quasi random sequences which produce a more ordered disposition of the centers with respect to the PVT case. A probability density function for volumes of these Sobol Voronoi tessellations (SVT) will be proposed and compared with results of numerical simulations. An application will be presented concerning the local structure of gas ($CO_2$) in the liquid-gas coexistence phase. Furthermore a probability distribution will be computed for the length of chords resulting from the intersections of random lines with a three-dimensional SVT. The agreement of the analytical formula with the results from a computer simulation will be also investigated. Finally a new type of Voronoi tessellation based on adjustable positions of seeds has been introduced which generalizes both PVT and SVT cases.

physics.data-an↗

arXiv2015

On the number of galaxies at high redshift

The number of galaxies at a given flux as a function of the redshift, $z$, is derived when the $z$-distance relation is non-standard. In order to compare different models, the same formalism is also applied to the standard cosmology. The observed luminosity function for galaxies of the zCOSMOS catalog at different redshifts is modelled by a new luminosity function for galaxies, which is derived by the truncated beta probability density function. Three astronomical tests, which are the photometric maximum as a function of the redshift for a fixed flux, the mean value of the redshift for a fixed flux, and the luminosity function for galaxies as a function of the redshift, compare the theoretical values of the standard and non-standard model with the observed value. The tests are performed on the FORS Deep Field (FDF) catalog up to redshift $z=1.5$ and on the zCOSMOS catalog extending beyond $z=4$. These three tests show minimal differences between the standard and the non-standard models.

astro-ph.CO↗

arXiv2015

Classical and relativistic conservation of momentum flux in radio-galaxies

A new set of laws of motion for turbulent jets propagating in an intergalactic medium characterized by a decreasing density is derived by applying conservation of momentum flux both in the classical and relativistic framework. Two characteristic features of radio-galaxies, such as oscillations and curvature, are modeled by a classical helicoidal jet. A third feature of a radio-galaxy, the appearance of knots, is explained as an effect due to the theory of images.

astro-ph.HE↗

arXiv2015

Relativistic scaling laws for the light curve in supernovae

In order to explain light curve (LC) for Supernova (SN) we derive a classical formula for the conversion of the flux of kinetic energy into radiation. We then introduce a correction for the absorption adopting an optical depth as function of the time. The developed framework allows to fit the LC of type Ia SN 2005cf ( B and V ) and type IIp SN 2004A (B,V,I and R ). A relativistic formula for the flux of kinetic energy is also derived in terms of a Taylor expansion and the application is done to the LC of GRB 050814. The decay of the radioactive isotopes as a driver the LC for SNs is also reviewed and a new formulation is introduced. The Arnett's formula for bolometric luminosity is corrected for the optical depth and applied to SN 2001ay.

astro-ph.HE↗

arXiv2014

A classical and a relativistic law of motion for spherical supernovae

In this paper we derive some first order differential equations which model the classical and the relativistic thin layer approximations. The circumstellar medium is assumed to follow a density profile of Plummer type, or of Lane--Emden ($n=5$) type, or a power law. The first order differential equations are solved analytically, or numerically, or by a series expansion, or by recursion. The initial conditions are chosen in order to model the temporal evolution of SN 1993J over ten years and a smaller chi-squared is obtained for the Plummer case with eta=6. The stellar mass ejected by the SN progenitor prior to the explosion, expressed in solar mass, is identified with the total mass associated with the selected density profile and varies from $0.217 $ to $0.402 $ when the central number density is $10^7 $ particles per cubic centimeter. The Full width at half maximum of the three density profiles, which can be identified with the size of the Pre-SN 1993J envelope, varies from 0.0071 pc to 0.0092 pc.

astro-ph.GA↗

arXiv2014

Anisotropy in the Hubble constant as modeled by density gradients

The all-sky maps of the observed variation of the Hubble constant can be reproduced from a theoretical point of view by introducing an intergalactic plasma with a variable number density of electrons. The observed averaged value and variance of the Hubble constant are reproduced by adopting a rim model, an auto-gravitating model, and a Voronoi diagrams model as the backbone for an auto-gravitating medium. We also analyze an astronomer's model based on the 3D spatial distribution of galaxies as given by the 2MASS Redshift Survey and an auto-gravitating Lane--Emden ($n=5$) profile of the electrons. The simulation which involves the Voronoi diagrams is done in a cubic box with sides of 100 Mpc. The simulation which involves the 2MASS covers the range of redshift smaller than 0.05.

astro-ph.CO↗

arXiv2014

The relativistic three dimensional evolution of SN 1987A

The high velocities observed in supernovae require a relativistic treatment for the equation of motion in the presence of gradients in the density of the interstellar medium. The adopted theory is that of the thin layer approximation. The chosen medium is auto-gravitating with respect to an equatorial plane. The differential equation which governs the relativistic conservation of momentum is solved in numerically and by recursion. The asymmetric field of relativistic velocities as well the time dilation are plotted at the age of 1 yr for SN 1987A.

astro-ph.SR↗

arXiv2014

A near infrared test for two recent luminosity functions for galaxies

Two recent luminosity function (LF) for galaxies are reviewed and the parameters which characterize the near infrared are fixed. A first LF is a modified Schechter LF with four parameters. The second LF is derived from the generalized gamma and has four parameters. The formulas which give the number of galaxies as function of the redshift are reviewed and a special attention is given to the position of the photometric maximum which is expressed as function of a critical parameter or the flux of radiation or the apparent magnitude. A simulation of the 2MASS Redshift Survey is given in the framework of the non Poissonian Voronoi Tessellation.

astro-ph.CO↗