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Remo Ruffini

Publications and source records attributed to Remo Ruffini.

At least 73 records · Page 4Linked to original sources
arXiv2012

Neutrinos decoupled from $β$-processes and supernova explosion

Based on the gravitational collapse time-scale is larger than the weak interaction time-scale at core densities $ρ> 10^{11} {gr}/ {cm}^{3}$, we approximately use the $β$-equilibrium condition and particle number conservations to calculate the number and energy densities of neutrino sphere in the process of gravitational core collapse towards the formation of a proto-neutron star. We find that at core densities $ρ_{dec} > 10^{12} {gr}/ {cm}^{3}$, the $β$-equilibrium condition cannot be satisfied consistently with charge, baryon and lepton number conservations, leading to the presence of excess neutrinos decoupling from the $β$-equilibrium. These excess neutrinos interact with nucleons and electrons via the neutral current channel only and their diffusion time is about $10^{-2}$ sec. The excess neutrino flux could play an important role in an Supernova explosion, provided the fraction of excess neutrinos over all neutrinos is at least one present.

astro-ph.HE↗
arXiv2012

Cooling of young neutron stars in GRB associated to Supernova

Recent observations of the late ($t=10^8$--$10^9$ s) emission of supernovae (SNe) associated to GRBs (GRB-SN) show a distinctive emission in the X-ray regime consistent with temperatures $10^7$--$10^8$ K. Similar features have been also observed in the two Type Ic SNe SN 2002ap and SN 1994I that are not associated to GRBs. We advance the possibility that the late X-ray emission observed in GRB-SN and in isolated SN is associated to a hot neutron star (NS) just formed in the SN event, here defined as a neo-NS. We discuss the thermal evolution of neo-NS in the age regime that spans from $\sim 1$ minute (just after the proto-NS phase) up to ages <10-100 yr. We examine the key factor governing the neo-NS cooling emphasizing on the neutrino emission. A phenomenological heating source and new boundary conditions are introduced to mimic the high-temperature atmosphere of young NSs. We match the neo-NS luminosity to the late X-ray emission of the GRB-SN events URCA-1 in GRB980425-SN1998bw, URCA-2 in GRB030329-SN2003dh, and URCA-3 in GRB031203-SN2003lw. By calibrating our additional heating source at early times to $\sim 10^{12}$--$10^{15}$ erg/g/s, we find a striking agreement of the luminosity obtained from the cooling of neo-NSs with the late ($t=10^{8}$--$10^{9}$ s) X-ray emission observed in GRB-SN. It is therefore appropriate to revise the boundary conditions used in the cooling theory of NSs, to match the proper conditions of the atmosphere at young ages. Additional heating processes that are still not studied within this context, such as e+e- pair creation by overcritical fields and nuclear fusion and fission energy release, might also take place under such conditions and deserve further analysis. Observation of GRB-SN has shown the possibility of witnessing the thermal evolution of neo-NSs. A new campaign of dedicated observations is recommended both of GRB-SN and of isolated Type Ic SN.

astro-ph.HE↗
arXiv2012

Neutron star equilibrium configurations within a fully relativistic theory with strong, weak, electromagnetic, and gravitational interactions

We formulate the equations of equilibrium of neutron stars taking into account strong, weak, electromagnetic, and gravitational interactions within the framework of general relativity. The nuclear interactions are described by the exchange of the sigma, omega, and rho virtual mesons. The equilibrium conditions are given by our recently developed theoretical framework based on the Einstein-Maxwell-Thomas-Fermi equations along with the constancy of the general relativistic Fermi energies of particles, the "Klein potentials", throughout the configuration. The equations are solved numerically in the case of zero temperatures and for selected parametrization of the nuclear models. The solutions lead to a new structure of the star: a positively charged core at supranuclear densities surrounded by an electronic distribution of thickness $\sim \hbar/(m_e c)$ of opposite charge, as well as a neutral crust at lower densities. Inside the core there is a Coulomb potential well of depth $\sim m_πc^2/e$. The constancy of the Klein potentials in the transition from the core to the crust, impose the presence of an overcritical electric field $\sim (m_π/m_e)^2 E_c$, the critical field being $E_c=m^2_e c^3/(e \hbar)$. The electron chemical potential and the density decrease, in the boundary interface, until values $μ^{\rm crust}_e < μ^{\rm core}_e$ and $ρ_{\rm crust}<ρ_{\rm core}$. For each central density, an entire family of core-crust interface boundaries and, correspondingly, an entire family of crusts with different mass and thickness, exist. The configuration with $ρ_{\rm crust}=ρ_{\rm drip}\sim 4.3\times 10^{11}$ g/cm$^3$ separates neutron stars with and without inner crust. We present here the novel neutron star mass-radius for the case $ρ_{\rm crust}=ρ_{\rm drip}$ and compare and contrast it with the one obtained from the Tolman-Oppenheimer-Volkoff treatment.

astro-ph.SR↗
arXiv2011

SGRs and AXPs as rotation powered massive white dwarfs

SGR 0418+5729 is a "Rosetta Stone" for deciphering the energy source of Soft Gamma Ray Repeaters (SGRs) and Anomalous X-ray Pulsars (AXPs). We show a model based on canonical physics and astrophysics for SGRs and AXPs powered by massive highly magnetized rotating white dwarfs (WDs), in total analogy with pulsars powered by rotating neutron stars (NSs). We predict for SGR 0418+5729 a lower limit for its spin-down rate, $\dot{P} \geq L_X P^3/(4π^2 I)=1.18\times 10^{-16}$ where $I$ is the moment of inertia of the WD. We show for SGRs and AXPs that, the occurrence of the glitch and the gain of rotational energy, is due to the release of gravitational energy associated to the contraction and decrease of the moment of inertia of the WDs. The steady emission and the outburst following the glitch are explained by the loss of rotational energy of the Wds, in view of the much larger moment of inertia of the WDs, as compared to the one of NSs and/or quark stars. There is no need here to invoke the unorthodox concept of magnetic energy release due to decay of overcritical magnetic fields, as assumed in the magnetar model. A new astrophysical scenario for the SGRs and AXPs associated to Supernova remnants is presented. The observational campaigns of the X-ray Japanese satellite Suzaku on AE Aquarii and the corresponding theoretical works by Japanese groups and recent results of the Hubble Space Telescope, give crucial information for our theoretical model. Follow-on missions of Hubble Telescope and VLT are highly recommended to give further observational evidence of this most fundamental issue of relativistic astrophysics: the identification of the true SGRs/AXPs energy source.

astro-ph.SR↗
arXiv2011

The luminosity evolution over the EQuiTemporal Surfaces in the prompt emission of Gamma-Ray Bursts

Due to the ultrarelativistic velocity of the expanding "fireshell" (Lorentz gamma factor γ\sim 10^2 - 10^3), photons emitted at the same time from the fireshell surface do not reach the observer at the same arrival time. In interpreting Gamma-Ray Bursts (GRBs) it is crucial to determine the properties of the EQuiTemporal Surfaces (EQTSs): the locus of points which are source of radiation reaching the observer at the same arrival time. In the current literature this analysis is performed only in the latest phases of the afterglow. Here we study the distribution of the GRB bolometric luminosity over the EQTSs, with special attention to the prompt emission phase. We analyze as well the temporal evolution of the EQTS apparent size in the sky. We use the analytic solutions of the equations of motion of the fireshell and the corresponding analytic expressions of the EQTSs which have been presented in recent works and which are valid for both the fully radiative and the adiabatic dynamics. We find the novel result that at the beginning of the prompt emission the most luminous regions of the EQTSs are the ones closest to the line of sight. On the contrary, in the late prompt emission and in the early afterglow phases the most luminous EQTS regions are the ones closest to the boundary of the visible region. This transition in the emitting region may lead to specific observational signatures, i.e. an anomalous spectral evolution, in the rising part or at the peak of the prompt emission. We find as well an expression for the apparent radius of the EQTS in the sky, valid in both the fully radiative and the adiabatic regimes. Such considerations are essential for the theoretical interpretation of the prompt emission phase of GRBs.

astro-ph.HE↗
arXiv2011

On the equilibrium of self-gravitating neutrons, protons and electrons in β-equilibrium

We have recently proved the impossibility of imposing the condition of local charge neutrality in a self-gravitating system of degenerate neutrons, protons and electrons in $β$-equilibrium. The coupled system of the general relativistic Thomas-Fermi equations and the Einstein-Maxwell equations have been shown to supersede the traditional Tolman-Oppenheimer-Volkoff equations. Here we present the Newtonian limit of the new equilibrium equations. We also extend the treatment to the case of finite temperatures and finally we give the explicit demonstration of the constancy of the Klein potentials in the case of finite temperatures generalizing the condition of constancy of the general relativistic Fermi energies in the case of zero temperatures.

astro-ph.SR↗
arXiv2011

Equatorial circular motion in Kerr spacetime

We analyze the properties of circular orbits of test particles on the equatorial plane of a rotating central mass whose gravitational field is described by the Kerr spacetime. For rotating black holes and naked singularities we explore all the spatial regions where circular orbits can exist and analyze the behavior of the energy and the angular momentum of the corresponding test particles. In particular, we find all the radii at which a test particle can have zero angular momentum due to the repulsive gravity effects generated by naked singularities. We classify all the stability zones of circular orbits. It is shown that the geometric structure of the stability zones of black holes is completely different from that of naked singularities.

gr-qc↗
arXiv2011

Electron-positron pairs production in a macroscopic charged core

Classical and semi-classical energy states of relativistic electrons bounded by a massive and charged core with the charge-mass-radio Q/M and macroscopic radius R_c are discussed. We show that the energies of semi-classical (bound) states can be much smaller than the negative electron mass-energy (-mc^2), and energy-level crossing to negative energy continuum occurs. Electron-positron pair production takes place by quantum tunneling, if these bound states are not occupied. Electrons fill into these bound states and positrons go to infinity. We explicitly calculate the rate of pair-production, and compare it with the rates of electron-positron production by the Sauter-Euler-Heisenberg-Schwinger in a constant electric field. In addition, the pair-production rate for the electro-gravitational balance ratio Q/M = 10^{-19} is much larger than the pair-production rate due to the Hawking processes.

hep-th↗
arXiv2011

On the nature of GRB 050509b: a disguised short GRB

(shortened) Context: GRB GRB 050509b, detected by the \emph{Swift} satellite, is the first case where an X-ray afterglow has been observed associated with a short gamma-ray burst (GRB). Within the fireshell model, the canonical GRB light curve presents two different components: the proper-GRB (P-GRB) and the extended afterglow. [...] In particular, the traditionally called short GRBs can be either "genuine" short GRBs [...] or "disguised" short GRBs [...]. AIMS: We verify whether GRB 050509b can be classified as a "genuine" short or a "disguised" short GRB, in the fireshell model. Methods: We investigate two alternative scenarios. In the first, we start from the assumption that this GRB is a "genuine" short burst. In the second attempt, we assume that this GRB is a "disguised" burst. Results: If GRB 050509b were a genuine short GRB, there should initially be very hard emission which is ruled out by the observations. The analysis that assumes that this is a disguised short GRB is compatible with the observations. The theoretical model predicts a value of the extended afterglow energy peak that is consistent with the Amati relation. Conclusions: GRB 050509b cannot be classified as a "genuine" short GRB. The observational data are consistent with a "disguised" short GRB classification, i.e., a long burst with a weak extended afterglow "deflated" by the low density of the CBM. We expect that all short GRBs with measured redshifts are disguised short GRBs because of a selection effect: if there is enough energy in the afterglow to measure the redshift, then the proper GRB must be less energetic than the afterglow. The Amati relation is found to be fulfilled only by the extended afterglow excluding the P-GRB.

astro-ph.HE↗
arXiv2010

GRB 071227: an additional case of a disguised short burst

(shortened) [...] In the context of the fireshell model, [...] a new family of disguised short bursts has been identified: long bursts with a protracted low instantaneous luminosity due to a low density CircumBurst Medium (CBM). In the 15-150 keV energy band GRB 071227 exhibits a short duration (about 1.8s) spike-like emission followed by a very soft extended tail up to one hundred seconds after the trigger. It is a faint (E_{iso}=5.8x10^{50}) nearby GRB (z=0.383) that does not have an associated type Ib/c bright supernova (SN). For these reasons, GRB 071227 has been classified as a short burst not fulfilling the Amati relation holding for long burst. We check the classification of GRB 071227 provided by the fireshell model. In particular, we test whether this burst is another example of a disguised short burst, after GRB 970228 and GRB 060614, and, for this reason, whether it fulfills the Amati relation. We simulate GRB 071227 light curves in the Swift BAT 15-50 keV bandpass and in the XRT (0.3-10 keV) energy band within the fireshell model. We perform simulations of the tail in the 15-50 keV bandpass, as well as of the first part of the X-ray afterglow. This infers that: E_{tot}^{e^\pm}=5.04x10^{51} erg, B=2.0x10^{-4}, E_{P-GRB}/E_{aft}~0.25, and =3.33 particles/cm^3. These values are consistent with those of "long duration" GRBs. We interpret the observed energy of the first hard emission by identifying it with the P-GRB emission. The remaining long soft tail indeed fulfills the Amati relation. Previously classified as a short burst, GRB 071227 on the basis of our analysis performed in the context of the fireshell scenario represents another example of a disguised short burst, after GRB 970228 and GRB 060614. Further confirmation of this result is that the soft tail of GRB 071227 fulfills the Amati relation.

astro-ph.HE↗
arXiv2010

Electron-positron pair oscillation in spatially inhomogeneous electric fields and radiation

It is known that strong electric fields produce electron and positron pairs from the vacuum, and due to the back-reaction these pairs oscillate back and forth coherently with the alternating electric fields in time. We study this phenomenon in spatially inhomogeneous and bound electric fields by integrating the equations of energymomentum and particle-number conservations and Maxwell equations. The space and time evolutions of the pair-induced electric field, electric charge- and currentdensities are calculated. The results show that non-vanishing electric charge-density and the propagation of pair-induced electric fields, differently from the case of homogeneous and unbound electric fields. The space and time variations of pair-induced electric charges and currents emit an electromagnetic radiation. We obtain the narrow spectrum and intensity of this radiation, whose peak ωpeak locates in the region around 4 KeV for electric field strength \sim Ec. We discuss their relevances to both the laboratory experiments for electron and positron pair-productions and the astrophysical observations of compact stars with an electromagnetic structure.

hep-ph↗
arXiv2010

Circular motion in Reissner-Nordström spacetime

We study the motion of neutral test particles along circular orbits in the Reissner-Nordström spacetime. We use the method of the effective potential with the constants of motion associated to the underlying Killing symmetries. A comparison between the black hole and naked singularity cases is performed. In particular we find that in the naked singularity case for $r Q^2/M$ and $1 \sqrt{5}/2$ there are all stable circular orbits for $r>Q^2/M$.

gr-qc↗
arXiv2009

On the self-consistent general relativistic equilibrium equations of neutron stars

We address the existence of globally neutral neutron star configurations in contrast with the traditional ones constructed by imposing local neutrality. The equilibrium equations describing this system are the Einstein-Maxwell equations which must be solved self-consistently with the general relativistic Thomas-Fermi equation and $β$-equilibrium condition. To illustrate the application of this novel approach we adopt the Baym, Bethe, and Pethick (1971) strong interaction model of the baryonic matter in the core and of the white-dwarf-like material of the crust. We illustrate the crucial role played by the boundary conditions satisfied by the leptonic component of the matter at the interface between the core and the crust. For every central density an entire new family of equilibrium configurations exists for selected values of the Fermi energy of the electrons at the surface of the core. Each such configuration fulfills global charge neutrality and is characterized by a non-trivial electrodynamical structure. The electric field extends over a thin shell of thickness $\sim \hbar/(m_e c)$ between the core and the crust and becomes largely overcritical in the limit of decreasing values of the crust mass.

astro-ph.SR↗
arXiv2009

Electron-positron pairs in physics and astrophysics: from heavy nuclei to black holes

From the interaction of physics and astrophysics we are witnessing in these years a splendid synthesis of theoretical, experimental and observational results originating from three fundametal physical processes. They were originally proposed by Dirac, by Breit and Wheeler and by Sauter, Heisenberg, Euler and Schwinger. The vacuum polarization process in strong electromagnetic field, pioneered by Sauter, Heisenberg, Euler and Schwinger, introduced the concept of critical electric field. It has been searched without success for more than forty years by heavy-ion collisions in many of the leading particle accelerators worldwide. The novel situation today is that these same processes can be studied on a much more grandiose scale during the gravitational collapse leading to the formation of a black hole being observed in Gamma Ray Bursts. This report is dedicated to the scientific race in act. The theoretical and experimental work developed in Earth-based laboratories is confronted with the theoretical interpretation of space-based observations of phenomena originating on cosmological scales. What has become clear in the last ten years is that all the three above mentioned processes, duly extended in the general relativistic framework, are necessary for the understanding of the physics of the gravitational collapse to a black hole. Vice versa, the natural arena where these processes can be observed in mutual interaction and on an unprecedented scale, is indeed the realm of relativistic astrophysics.

astro-ph.HE↗
arXiv2009

The Blackholic energy and the canonical Gamma-Ray Burst IV: the "long", "genuine short" and "fake - disguised short" GRBs

(Shortened) [...] After recalling the basic features of the "fireshell model", we emphasize the following novel results: 1) the interpretation of the X-ray flares in GRB afterglows as due to the interaction of the optically thin fireshell with isolated clouds in the CircumBurst Medium (CBM); 2) an interpretation as "fake - disguised" short GRBs of the GRBs belonging to the class identified by Norris & Bonnell [...] consistent with an origin from the final coalescence of a binary system in the halo of their host galaxies with particularly low CBM density [...]; 3) the first attempt to study a genuine short GRB with the analysis of GRB 050509B, that reveals indeed still an open question; 4) the interpretation of the GRB-SN association in the case of GRB 060218 via the "induced gravitational collapse" process; 5) a first attempt to understand the nature of the "Amati relation", a phenomenological correlation between the isotropic-equivalent radiated energy of the prompt emission E_{iso} with the cosmological rest-frame νF_ν spectrum peak energy E_{p,i}. In addition, recent progress on the thermalization of the electron-positron plasma close to their formation phase, as well as the structure of the electrodynamics of Kerr-Newman Black Holes are presented. An outlook for possible explanation of high-energy phenomena in GRBs to be expected from the AGILE and the Fermi satellites are discussed. As an example of high energy process, the work by Enrico Fermi dealing with ultrarelativistic collisions is examined. It is clear that all the GRB physics points to the existence of overcritical electrodynamical fields. In this sense we present some progresses on a unified approach to heavy nuclei and neutron stars cores, which leads to the existence of overcritical fields under the neutron star crust.

astro-ph.HE↗
arXiv2009

Analytic Solutions of the Ultra-relativistic Thomas-Fermi Equation

It is well known that the ultra-relativistic Thomas-Fermi equation, amply adopted in the study of heavy nuclei, admits an exact solution for a constant proton distribution within a spherical core of radius Rc. Here exact solutions of a generalized ultra-relativistic Thomas-Fermi equation are presented, assuming a Wood-Saxon-like proton distribution and its further generalizations. These solutions present an overcritical electric field close to their surface. The variation of the electric fields as a function of the generalized Wood-Saxon parameters are studied.

astro-ph.SR↗