arXiv subjects

R. Ruffini

Publications and source records attributed to R. Ruffini.

At least 127 records · Page 7Linked to original sources

arXiv2012

A double component in GRB 090618: a proto-black hole and a genuinely long GRB

The joint X and gamma-ray observations of GRB 090618 by a large number of satellites offer an unprecedented possibility of testing crucial aspects of theoretical models. In particular, it allows us to test (a) the formation of an optically thick e+e- baryon plasma self-accelerating to Lorentz factors in the range 200 < g < 3000; (b) its transparency condition with the emission of a component of 10^{53-54} baryons in the TeV region and (c) the collision of these baryons with the circumburst medium clouds, characterized by dimensions of 10^{15-16} cm. In addition, these observations offer the possibility of testing a new understanding of the thermal and power-law components in the early phase of this GRB. We test the fireshell model of GRBs in one of the closest (z = 0.54) and most energetic (Eiso = 2.90 x 10^{53} ergs) GRBs, namely GRB 090618. We analyze its emission using several spectral models, with special attention to the thermal and power-law components. We determine the fundamental parameters of a canonical GRB within the context of the fireshell model. We find evidences of the existence of two different episodes in GRB 090618. The first episode lasts 50 s and is characterized by a spectrum consisting of thermal component, which evolves between kT = 54 keV and kT = 12 keV. The second episode, which lasts for \sim 100s, behaves as a canonical long GRB with a Lorentz gamma factor at transparency of g = 495, a temperature at transparency of 29.22 keV and with characteristic masses of the surrounding clouds of \sim 10^{22-24} g. We support the recently proposed two-component nature of GRB 090618 by using specific theoretical analysis and illustrate that the episode 1 cannot be considered to be either a GRB or a part of a GRB event, but it appears to be related to the progenitor of the collapsing bare core leading to the formation of the black hole which we call a proto-black hole.

astro-ph.HE↗

arXiv2012

Evidence for a proto-black hole and a double astrophysical component in GRB 101023

[Shortened] Context: [...] we point out a striking similarity between GRB 101023 and GRB 090618. We explore the possibility that these sources are members of a new GRB family related to a single core-collapse. We use this understanding of the source in order to infer the unobserved redshift of GRB 101023. [...]. Aims: In precise analogy with GRB 090618 we aim to analyze the 89s of emission of GRB 101023 to see if we are in presence of two different episodes: the first one presenting a characteristic Black-body temperature evolution, evolving in time with a broken power-law, and the second one consistent with a canonical GRB. [...] Results: We confirm that the first episode can be well fit by a Black body plus a power-law model. The temperature changes with time following a broken power law, and the photon index of the power-law component presents a soft to hard evolution. We estimate the radius of this source, increasing with time with a velocity of 1.5x10^4 km/s. The second episode appears to be a canonical GRB. By using the Amati relation and the Atteia relation, we determine the cosmological redshift, z ~ 0.9 +- 0.084 (stat.) +- 0.2 (sys.). [...]. Particularly striking is the scaling law of the soft X-ray component of the afterglow. Conclusions: We identify GRB 090618 and GRB 101023 with a new family of GRBs presenting a double astrophysical component. A first one, related to the proto-black hole, prior to the process of gravitational collapse (episode 1) and a second one which is the canonical GRB (episode 2) emitted during the formation of the black-hole. [...] This analysis indicates progress towards developing a GRB distance indicator based on the understanding of the P-GRB and the prompt radiation as well as the soft X-Ray behavior of the late afterglow.

astro-ph.HE↗

arXiv2011

Evidences for a double component in GRB 101023

We present the results of the analysis of GRB 101023 in the fireshell scenario. Its redshift has not been determined due to the lack of data in the optical band, so we tried to infer it from the Amati Relation, obtaining z=0.9. Its light curve presents a double emission, which makes it very similar to the already studied GRB 091018. We performed a time-resolved spectral analysis with XSPEC using different spectral models, and fitted the light curve with the numerical code GRBsim. We used Fermi GBM data to build the light curve, in particular the second INa detector, in the range (8-440 keV). We found that the first emission does not match the requirements for a GRB, while the second part perfectly agrees with being a canonical GRB, with a P-GRB lasting 4s.

astro-ph.HE↗

arXiv2011

A double component in the prompt emission of GRB 090618

GRB 090618 offered an unprecedented opportunity to have coordinated data, by the best of the X and Gamma Ray observatories, of the nearest (z = 0.54) energetic source (10$^{54}$ erg). Using the Fermi-GBM observations of this GRB, we have analyzed this source to explore the possibility of having components yet to be observed in other sources. We show that it is not possible to interpret GRB 090618 within the framework of the traditional single component GRB model. We argue that the observation of the first episode of duration of around 50s could not be a part of a canonical GRB, while the residual emission could be modeled easily with the models existing in literature. In this work we have considered the case of the fireshell scenario.

astro-ph.HE↗

arXiv2011

The Klein first integrals in an equilibrium system with electromagnetic, weak, strong and gravitational interactions

The isothermal Tolman condition and the constancy of the Klein potentials originally expressed for the sole gravitational interaction in a single fluid are here generalized to the case of a three quantum fermion fluid duly taking into account the strong, electromagnetic, weak and gravitational interactions. The set of constitutive equations including the Einstein-Maxwell-Thomas-Fermi equations as well as the ones corresponding to the strong interaction description are here presented in the most general relativistic isothermal case. This treatment represents an essential step to correctly formulate a self-consistent relativistic field theoretical approach of neutron stars.

gr-qc↗

arXiv2011

The relativistic Feynman-Metropolis-Teller theory for white-dwarfs in general relativity

The recent formulation of the relativistic Thomas-Fermi model within the Feynman-Metropolis-Teller theory for compressed atoms is applied to the study of general relativistic white dwarf equilibrium configurations. The equation of state, which takes into account the β-equilibrium, the nuclear and the Coulomb interactions between the nuclei and the surrounding electrons, is obtained as a function of the compression by considering each atom constrained in a Wigner-Seitz cell. The contribution of quantum statistics, weak, nuclear, and electromagnetic interactions is obtained by the determination of the chemical potential of the Wigner-Seitz cell. The further contribution of the general relativistic equilibrium of white dwarf matter is expressed by the simple formula $\sqrt{g_{00}}μ_{\rm ws}$= constant, which links the chemical potential of the Wigner-Seitz cell $μ_{\rm ws}$ with the general relativistic gravitational potential $g_{00}$ at each point of the configuration. The configuration outside each Wigner-Seitz cell is strictly neutral and therefore no global electric field is necessary to warranty the equilibrium of the white dwarf. These equations modify the ones used by Chandrasekhar by taking into due account the Coulomb interaction between the nuclei and the electrons as well as inverse β-decay. They also generalize the work of Salpeter by considering a unified self-consistent approach to the Coulomb interaction in each Wigner-Seitz cell. The consequences on the numerical value of the Chandrasekhar-Landau mass limit as well as on the mass-radius relation of $^4$He, $^{12}$C, $^{16}$O and $^{56}$Fe white dwarfs are presented. All these effects should be taken into account in processes requiring a precision knowledge of the white dwarf parameters.

astro-ph.SR↗

arXiv2011

The self-consistent general relativistic solution for a system of degenerate neutrons, protons and electrons in beta-equilibrium

We present the self-consistent treatment of the simplest, nontrivial, self-gravitating system of degenerate neutrons, protons and electrons in $β$-equilibrium within relativistic quantum statistics and the Einstein-Maxwell equations. The impossibility of imposing the condition of local charge neutrality on such systems is proved, consequently overcoming the traditional Tolman-Oppenheimer-Volkoff treatment. We emphasize the crucial role of imposing the constancy of the generalized Fermi energies. A new approach based on the coupled system of the general relativistic Thomas-Fermi-Einstein-Maxwell equations is presented and solved. We obtain an explicit solution fulfilling global and not local charge neutrality by solving a sophisticated eigenvalue problem of the general relativistic Thomas-Fermi equation. The value of the Coulomb potential at the center of the configuration is $eV(0)\simeq m_πc^2$ and the system is intrinsically stable against Coulomb repulsion in the proton component. This approach is necessary, but not sufficient, when strong interactions are introduced.

gr-qc↗

arXiv2011

Motion of charged test particles in Reissner--Nordström spacetime

We investigate the circular motion of charged test particles in the gravitational field of a charged mass described by the Reissner-Nordström (RN) spacetime. We study in detail all the spatial regions where circular motion is allowed around either black holes or naked singularities. The effects of repulsive gravity are discussed by finding all the circles at which a particle can have vanishing angular momentum. We show that the geometric structure of stable accretion disks, made of only test particles moving along circular orbits around the central body, allows us to clearly distinguish between black holes and naked singularities.

gr-qc↗

arXiv2011

On the frequency of oscillations in the pair plasma generated by a strong electric field

We study the frequency of the plasma oscillations of electron-positron pairs created by the vacuum polarization in an uniform electric field with strength E in the range 0.2 Ec < E < 10 Ec. Following the approach adopted in [1] we work out one second order ordinary differential equation for a variable related to the velocity from which we can recover the classical plasma oscillation equation when E -> 0. Thereby, we focus our attention on its evolution in time studying how this oscillation frequency approaches the plasma frequency. The time-scale needed to approach to the plasma frequency and the power spectrum of these oscillations are computed. The characteristic frequency of the power spectrum is determined uniquely from the initial value of the electric field strength. The effects of plasma degeneracy and pair annihilation are discussed.

physics.plasm-ph↗

arXiv2010

Circular motion of neutral test particles in Reissner-Nordström spacetime

We investigate the motion of neutral test particles in the gravitational field of a mass $M$ with charge $Q$ described by the Reissner-Nordström (RN) spacetime. We focus on the study of circular stable and unstable orbits around configurations describing either black holes or naked singularities. We show that at the classical radius, defined as $Q^2/M$, there exist orbits with zero angular momentum due to the presence of repulsive gravity. The analysis of the stability of circular orbits indicates that black holes are characterized by a continuous region of stability. In the case of naked singularities, the region of stability can split into two non-connected regions inside which test particles move along stable circular orbits.

astro-ph.HE↗

arXiv2010

On the relativistic Thomas-Fermi treatment of compressed atoms and compressed nuclear matter cores of stellar dimensions

The Feynman, Metropolis and Teller treatment of compressed atoms is extended to the relativistic regimes. Each atomic configuration is confined by a Wigner-Seitz cell and is characterized by a positive electron Fermi energy. The non-relativistic treatment assumes a point-like nucleus and infinite values of the electron Fermi energy can be attained. In the relativistic treatment there exists a limiting configuration, reached when the Wigner-Seitz cell radius equals the radius of the nucleus, with a maximum value of the electron Fermi energy $(E_e^F)_{max}$, here expressed analytically in the ultra-relativistic approximation. The corrections given by the relativistic Thomas-Fermi-Dirac exchange term are also evaluated and shown to be generally small and negligible in the relativistic high density regime. The dependence of the relativistic electron Fermi energies by compression for selected nuclei are compared and contrasted to the non-relativistic ones and to the ones obtained in the uniform approximation. The relativistic Feynman, Metropolis, Teller approach here presented overcomes some difficulties in the Salpeter approximation generally adopted for compressed matter in physics and astrophysics. The treatment is then extrapolated to compressed nuclear matter cores of stellar dimensions with $A\simeq (m_{\rm Planck}/m_n)^3 \sim 10^{57}$ or $M_{core}\sim M_{\odot}$. A new family of equilibrium configurations exists for selected values of the electron Fermi energy varying in the range $0 < E_e^F \leq (E_e^F)_{max}$. Such configurations fulfill global but not local charge neutrality. They have electric fields on the core surface, increasing for decreasing values of the electron Fermi energy reaching values much larger than the critical value $E_c = m_e^2c^3/(e\hbar)$, for $E_e^F=0$. We compare and contrast our results with the ones of Thomas-Fermi model in strange stars.

astro-ph.SR↗

arXiv2010

Pair plasma relaxation time scales

By numerically solving the relativistic Boltzmann equations, we compute the time scale for relaxation to thermal equilibrium for an optically thick electron-positron plasma with baryon loading. We focus on the time scales of electromagnetic interactions. The collisional integrals are obtained directly from the corresponding QED matrix elements. Thermalization time scales are computed for a wide range of values of both the total energy density (over 10 orders of magnitude) and of the baryonic loading parameter (over 6 orders of magnitude). This also allows us to study such interesting limiting cases as the almost purely electron-positron plasma or electron-proton plasma as well as intermediate cases. These results appear to be important both for laboratory experiments aimed at generating optically thick pair plasmas as well as for astrophysical models in which electron-positron pair plasmas play a relevant role.

astro-ph.HE↗

arXiv2009

$e^-e^+$ pair creation by vacuum polarization around electromagnetic black holes

The concept of "dyadotorus" was recently introduced to identify in the Kerr-Newman geometry the region where vacuum polarization processes may occur, leading to the creation of $e^--e^+$ pairs. This concept generalizes the original concept of "dyadosphere" initially introduced for Reissner-Nordström geometries. The topology of the axially symmetric dyadotorus is studied for selected values of the electric field and its electromagnetic energy is estimated by using three different methods all giving the same result. It is shown by a specific example the difference between a dyadotorus and a dyadosphere. The comparison is made for a Kerr-Newman black hole with the same total mass energy and the same charge to mass ratio of a Reissner-Nordström black hole. It turns out that the Kerr-Newman black hole leads to larger values of the electromagnetic field and energy when compared to the electric field and energy of the Reissner-Nordström one. The significance of these theoretical results for the realistic description of the process of gravitational collapse leading to black hole formation as well as the energy source of gamma ray bursts are also discussed.

astro-ph.HE↗

arXiv2009

The Extended Nuclear Matter Model with Smooth Transition Surface

The existence of electric fields close to their critical value $E_c=\frac{m_e^2 c^3}{e \hbar}$ has been proved for massive cores of $10^7$ up to $10^{57}$ nucleons using a proton distribution of constant density and a sharp step function at its boundary. We explore the modifications of this effect by considering a smoother density profile with a proton distribution fulfilling a Woods--Saxon dependence. The occurrence of a critical field has been confirmed. We discuss how the location of the maximum of the electric field as well as its magnitude is modified by the smoother distribution.

astro-ph.SR↗

arXiv2009

Thermalization of the mildly relativistic plasma

In the recent Letter [1] we considered the approach of nonequilibrium pair plasma towards thermal equilibrium state adopting a kinetic treatment and solving numerically the relativistic Boltzmann equations. It was shown that plasma in the energy range 0.1-10 MeV first reaches kinetic equilibrium, on a timescale t_{k}<10^{-14} sec, with detailed balance between binary interactions such as Compton, Bhabha and Moller scattering, and pair production and annihilation. Later the electron-positron-photon plasma approaches thermal equilibrium on a timescale t_{th}<10^{-12} sec, with detailed balance for all direct and inverse reactions. In the present paper we systematically present details of the computational scheme used in [1], as well as generalize our treatment, considering proton loading of the pair plasma. When proton loading is large, protons thermalize first by proton-proton scattering, and then with the electron-positron-photon plasma by proton-electron scattering. In the opposite case of small proton loading proton-electron scattering dominates over proton-proton one. Thus in all cases the plasma, even with proton admixture, reaches thermal equilibrium configuration on a timescale t_{th}<10^{-11} sec. We show that it is crucial to account for not only binary but also triple direct and inverse interactions between electrons, positrons, photons and protons. Several explicit examples are given and the corresponding timescales for reaching kinetic and thermal equilibria are determined.

astro-ph.HE↗

arXiv2008

Neutral nuclear core vs super charged one

Based on the Thomas-Fermi approach, we describe and distinguish the electron distributions around extended nuclear cores: (i) in the case that cores are neutral for electrons bound by protons inside cores and proton and electron numbers are the same; (ii) in the case that super charged cores are bare, electrons (positrons) produced by vacuum polarization are bound by (fly into) cores (infinity).

astro-ph↗

arXiv2007

Extended Schouten classification for non-Riemannian geometries

A generalized connection, including Christoffel coefficients, torsion, non-metricity tensor and metric-asymmetricity object, is analyzed according to the Schouten classification. The inverse structure matrix is found in the linearized regime, autoparallel trajectories are defined and the contribution of the components of the connection are clarified at first-order approximation.

gr-qc↗

arXiv2007

Thermalization of a nonequilibrium electron-positron-photon plasma

Starting from a nonequilibrium configuration we analyse the essential role of the direct and the inverse binary and triple interactions in reaching an asymptotic thermal equilibrium in a homogeneous isotropic electron-positron-photon plasma. We focus on energies in the range 0.1--10 MeV. We numerically integrate the integro-partial differential relativistic Boltzmann equation with the exact QED collisional integrals taking into account all binary and triple interactions in the plasma. We show that first, when detailed balance is reached for all binary interactions on a timescale $t_{k}\lesssim10^{-14}$sec, photons and electron-positron pairs establish kinetic equilibrium. Successively, when triple interactions fulfill the detailed balance on a timescale $t_{eq}\lesssim10^{-12}$sec, the plasma reaches thermal equilibrium. It is shown that neglecting the inverse triple interactions prevents reaching thermal equilibrium. Our results obtained in the theoretical physics domain also find application in astrophysics and cosmology.

physics.plasm-ph↗