arXiv subjects

Gregory Vereshchagin

Publications and source records attributed to Gregory Vereshchagin.

At least 19 recordsLinked to original sources

arXiv2026

Pair luminosity and cooling of newborn strange star: Color-flavor-locked and two-flavor color superconducting quarks

Following the previous wor k[1] here we consider early thermal evolution of hot strange stars made of color superconducting quarks in two different pairing states: two-flavor color superconductor (2SC) and color-flavor-locked (CFL) phases, taking into account cooling by neutrinos and electron-positron pair creation due to the Schwinger process. We show that Schwinger luminosity in the electrosphere is a universal function of temperature, independent of quark matter phase for quark chemical potential $\mu_q>280$ MeV. The surface of a strange star in all the cases cools faster than its interior. This leads to a fast decrease of pair luminosity with time, so that it does not exceed $10^{46}$ erg/s at 1 second after strange star formation. Neutrino luminosity dominates over pair luminosity in all the cases except for the CFL phase with a large gap parameter $\Delta>60$ MeV, where there is a strong suppression of neutrino emission. The total energy emitted in electron-positron pairs is always smaller than the energy emitted in neutrinos, but they become comparable for the large gap parameter.

astro-ph.HE↗

arXiv2026

Pair luminosity and cooling of newborn strange star: unpaired quarks

It was shown that pair luminosity of the newborn strange star with temperature of $10^{11}$ K may be as high as $L_\pm\simeq 10^{52}$ erg/s. The question remains: can a strange star maintain such a high surface temperature for a long time? To answer this question we studied thermal evolution of newborn strange star made of unpaired quarks taking into account its thermal conductivity and neutrino emission by the URCA processes $d\rightarrow u + e + \barν_e$ and $u+e\rightarrow d+ν_e$. Our results show that extremely high luminosity due to the Schwinger process and insufficient thermal conductivity of quarks leads to development of steep temperature gradient at the surface of strange star. As a result, the temperature at the surface and hence its luminosity decreases, reaching $10^{43}$ erg/s already at $10^2$ seconds. This result holds even in the presence of neutrinosphere.

astro-ph.HE↗

arXiv2025

Pair creation from radial electromagnetic perturbation of a compact astrophysical object

Recently Usov's mechanism of pair creation on the surface of compact astrophysical objects has been revisited [1] with a conclusion that the pair creation rate was previously underestimated in the literature by nearly two orders of magnitude. Here we consider an alternative hypothesis of pair creation due to a perturbation of the surface of a compact object. Radial perturbation is induced in hydrodynamic velocity resulting in a microscopic displacement of the negatively charged component with respect to the positively charged one. The result depends on the ratio between the spatial scale of the perturbation $λ$ and the mean free path $l$. When $λ\sim l$ the perturbation energy is converted into a burst of electron-positron pairs which are created in collisionless plasma oscillations at the surface; after energy excess is dissipated electrosphere returns to its electrostatic configuration. When instead $λ\gg l$, the perturbation is thermalized, its energy is transformed into heat, and pairs are created continuously by the heated electrosphere. We discuss the relevant astrophysical scenarios.

astro-ph.HE↗

arXiv2023

Pair creation in hot electrosphere of compact astrophysical objects

The mechanism of pair creation in electrosphere of compact astrophysical objects such as quark stars or neutron stars is revisited, paying attention to evaporation of electrons and acceleration of electrons and positrons, previously not addressed in the literature. We perform a series of numerical simulations using the Vlasov-Maxwell equations. The rate of pair creation strongly depends on electric field strength in the electrosphere. Despite Pauli blocking is explicitly taken into account, we find no exponential suppression of the pair creation rate at low temperatures. The luminosity in pairs increases with temperature and it may reach up to $L_\pm\sim 10^{52}$ erg/s, much larger than previously assumed.

astro-ph.HE↗

arXiv2023

Pauli blocking effects on pair creation in strong electric field

The process of electron-positron pair creation and oscillation in uniform electric field is studied, taking into account Pauli exclusion principle. Generally, we find that pair creation is suppressed, hence coherent oscillations occur on longer time scales. Considering pair creation in already existing electron-positron plasma we find that the dynamics depends on pair distribution function. We considered Fermi-Dirac distribution of pairs and found that for small temperatures pair creation is suppressed, while for small chemical potentials it increases: heating leads to enhancement of pair creation.

physics.plasm-ph↗

arXiv2022

Is magnetically dominated outflow required to explain GRBs?

The composition of relativistic outflows producing gamma-ray bursts is a long standing open question. One of the main arguments in favor of magnetically dominated outflows is the absence of photospheric component in their broadband time resolved spectra, with such notable example as GRB 080916C. Here, we perform a time-resolved analysis of this burst and confirm the previous detection of an additional spectral component. We show that this subdominant component is consistent with the photosphere of ultrarelativistic baryonic outflow, deep in the coasting regime. We argue that, contrary to previous statements, the magnetic dominance of the outflow is not required for the interpretation of this GRB. Moreover, simultaneous detection of high energy emission in its prompt phase requires departure from a one-zone emission model.

astro-ph.HE↗

arXiv2019

Probability of inflation in Loop Quantum Cosmology

We discuss how initial conditions for cosmological evolution can be defined in Loop Quantum Cosmology with massive scalar field and how the presence of the bounce influences the probability of inflation in this theory, compared with General Relativity. The main finding of the paper is existence of an attractor in the contracting phase of the universe, which results in special conditions at the bounce, quite independent on the measure of initial conditions in the remote past, and hence very specific duration of inflationary stage with the number of e-foldings about $140$.

gr-qc↗

arXiv2013

Physics of non-dissipative ultrarelativistic photospheres

Recent observations, especially by the Fermi satellite, point out the importance of the thermal component in GRB spectra. This fact revives strong interest in photospheric emission from relativistic outflows. Early studies already suggested that the observed spectrum of photospheric emission from relativistically moving objects differs in shape from the Planck spectrum. However, this component appears to be subdominant in many GRBs and the origin of the dominant component is still unclear. One of the popular ideas is that energy dissipation near the photosphere may produce a non-thermal spectrum and account for such emission. Before considering such models, though, one has to determine precise spectral and timing characteristics of the photospheric emission in the simplest possible case. Hence this paper focuses on various physical effects which make the photospheric emission spectrum different from the black body spectrum and quantifies them.

astro-ph.HE↗

arXiv2013

Electron-positron plasma in GRBs and in cosmology

Electron-positron plasma is believed to play imporant role both in the early Universe and in sources of Gamma-Ray Bursts (GRBs). We focus on analogy and difference between physical conditions of electron-positron plasma in the early Universe and in sources of GRBs. We discuss a) dynamical differences, namely thermal acceleration of the outflow in GRB sources vs cosmological deceleration; b) nuclear composition differences as synthesis of light elements in the early Universe and possible destruction of heavy elements in GRB plasma; c) different physical conditions during last scattering of photons by electrons. Only during the acceleration phase of the optically thick electron-positron plasma comoving observer may find it similar to the early Universe. This similarity breaks down during the coasting phase. Reprocessing of nuclear abundances may likely take place in GRB sources. Heavy nuclear elements are then destroyed, resulting mainly in protons with small admixture of helium. Unlike the primordial plasma which recombines to form neutral hydrogen, and emits the Cosmic Microwave Background Radiation, GRB plasma does not cool down enough to recombine.

astro-ph.CO↗

arXiv2013

Phase space evolution of pairs created in strong electric fields

We study the process of energy conversion from overcritical electric field into electron-positron-photon plasma. We solve numerically Vlasov-Boltzmann equations for pairs and photons assuming the system to be homogeneous and anisotropic. All the 2-particle QED interactions between pairs and photons are described by collision terms. We evidence several epochs of this energy conversion, each of them associated to a specific physical process. Firstly pair creation occurs, secondly back reaction results in plasma oscillations. Thirdly photons are produced by electron-positron annihilation. Finally particle interactions lead to completely equilibrated thermal electron-positron-photon plasma.

astro-ph.CO↗

arXiv2012

Analysis of GRB 080319B and GRB 050904 within the fireshell model: evidence for a broader spectral energy distribution

(Shortened) GRB080319B, with an isotropic energy E_{iso}=1.32x10^{54}erg, and GRB050904, with E_{iso}=1.04x10^{54}erg, offer the possibility of studying the spectral properties of the prompt radiation of two of the most energetic Gamma-Ray Bursts (GRBs). This allows us to probe the validity of the fireshell model for GRBs beyond 10^{54}erg, well outside the energy range where it has been successfully tested up to now (10^{49}-10^{53}erg). We find that in the low energy region, the prompt emission spectra observed by Swift BAT reveals more power than theoretically predicted. The opportunities offered by these observations to improve the fireshell model are outlined. One of the distinguishing features of the fireshell model is that it relates the observed spectra to the spectrum in the comoving frame of the fireshell. Originally, a fully radiative condition and a comoving thermal spectrum were adopted. An additional power-law in the comoving thermal spectrum is required [...] in the fireshell model for GRBs 080319B and 050904. A new phenomenological parameter αis correspondingly introduced in the model. We perform numerical simulations of the prompt emission in the Swift BAT bandpass by assuming different values of α[...]. We compare them with the GRB080319B and GRB050904 observed time-resolved spectra, as well as with their time-integrated spectra and light curves. Although GRB080319B and GRB050904 are at very different redshifts (z=0.937 and z=6.29 respectively), a value of α=-1.8 leads for both of them to a good agreement between the numerical simulations and the observed BAT light curves, time-resolved and time-integrated spectra. Such a modified spectrum is also consistent with the observations of previously analyzed less energetic GRBs and reasons for this additional agreement are given. Perspectives for future low energy missions are outlined.

astro-ph.HE↗

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

The canonical Gamma-Ray Bursts: long, "fake"-"disguised" and "genuine" short bursts

The Gamma-Ray Bursts (GRBs) offer the unprecedented opportunity to observe for the first time the blackholic energy extracted by the vacuum polarization during the process of gravitational collapse to a black hole leading to the formation of an electron-positron plasma. The uniqueness of the Kerr-Newman black hole implies that very different processes originating from the gravitational collapse a) of a single star in a binary system induced by the companion, or b) of two neutron stars, or c) of a neutron star and a white dwarf, do lead to the same structure for the observed GRB. The recent progress of the numerical integration of the relativistic Boltzmann equations with collision integrals including 2-body and 3-body interactions between the particles offer a powerful conceptual tool in order to differentiate the traditional "fireball" picture, an expanding hot cavity considered by Cavallo and Rees, as opposed to the "fireshell" model, composed of an internally cold shell of relativistically expanding electron-positron-baryon plasma. The analysis of the fireshell naturally leads to a canonical GRB composed of a proper-GRB and an extended afterglow. By recalling the three interpretational paradigms for GRBs we show how the fireshell model leads to an understanding of the GRB structure and to an alternative classification of short and long GRBs.

astro-ph.HE↗

arXiv2008

On Gamma-Ray Bursts

(Shortened) We show by example how the uncoding of Gamma-Ray Bursts (GRBs) offers unprecedented possibilities to foster new knowledge in fundamental physics and in astrophysics. After recalling some of the classic work on vacuum polarization in uniform electric fields by Klein, Sauter, Heisenberg, Euler and Schwinger, we summarize some of the efforts to observe these effects in heavy ions and high energy ion collisions. We then turn to the theory of vacuum polarization around a Kerr-Newman black hole, leading to the extraction of the blackholic energy, to the concept of dyadosphere and dyadotorus, and to the creation of an electron-positron-photon plasma. We then present a new theoretical approach encompassing the physics of neutron stars and heavy nuclei. It is shown that configurations of nuclear matter in bulk with global charge neutrality can exist on macroscopic scales and with electric fields close to the critical value near their surfaces. These configurations may represent an initial condition for the process of gravitational collapse, leading to the creation of an electron-positron-photon plasma: the basic self-accelerating system explaining both the energetics and the high energy Lorentz factor observed in GRBs. We then turn to recall the two basic interpretational paradigms of our GRB model. [...] We then turn to the special role of the baryon loading in discriminating between "genuine" short and long or "fake" short GRBs [...] We finally turn to the GRB-Supernova Time Sequence (GSTS) paradigm: the concept of induced gravitational collapse. [...] We then present some general conclusions.

astro-ph↗

arXiv2007

The Blackholic energy and the canonical Gamma-Ray Burst

We outline the main results of our GRB model, based on the three interpretation paradigms we proposed in July 2001, comparing and contrasting them with the ones in the current literature. Thanks to the observations by Swift and by VLT, this analysis points to a "canonical GRB" originating from markedly different astrophysical scenarios. The communality is that they are all emitted in the formation of a black hole with small or null angular momentum. The following sequence appears to be canonical: the vacuum polarization process creating an optically thick self accelerating electron-positron plasma; the engulfment of baryonic mass during the plasma expansion; the adiabatic expansion of the optically thick "fireshell" up to the transparency; the interaction of the remaining accelerated baryons with the interstellar medium (ISM). This leads to the canonical GRB composed of a proper GRB (P-GRB), emitted at the moment of transparency, followed by an extended afterglow. The parameters are the plasma total energy, the fireshell baryon loading and the ISM filamentary distribution around the source. In the limit of no baryon loading the total energy is radiated in the P-GRB. In this limit, the canonical GRBs explain as well the short GRBs.

astro-ph↗

arXiv2007

Equations of motion, initial and boundary conditions for GRB

We compare and contrast the different approaches to the optically thick adiabatic phase of GRB all the way to the transparency. Special attention is given to the role of the rate equation to be self consistently solved with the relativistic hydrodynamic equations. The works of Shemi and Piran (1990), Piran, Shemi and Narayan (1993), Meszaros, Laguna and Rees (1993) and Ruffini, Salmonson, Wilson and Xue (1999,2000) are compared and contrasted. The role of the baryonic loading in these three treatments is pointed out. Constraints on initial conditions for the fireball produced by electro-magnetic black hole are obtained.

astro-ph↗

arXiv2007

The role of GRB 031203 in clarifying the astrophysical GRB scenario

The luminosity and the spectral distribution of the afterglow of GRB 031203 have been presented within our theoretical framework, which envisages the GRB structure as composed by a proper-GRB, emitted at the transparency of an electron-positron plasma with suitable baryon loading, and an afterglow comprising the "prompt emission" as due to external shocks. In addition to the GRB emission, there appears to be a prolonged soft X-Ray emission lasting for 10^6-10^7 seconds followed by an exponential decay. This additional source has been called by us URCA-3. It is urgent to establish if this component is related to the GRB or to the Supernova (SN). In this second case, there are two possibilities: either the interaction of the SN ejecta with the interstellar medium or, possibly, the cooling of a young neutron star formed in the SN 2003lw process. The analogies and the differences between this triptych GRB 031203 / SN 2003lw / URCA-3 and the corresponding ones GRB 980425 / SN 1998bw / URCA-1 and GRB 030329 / SN 2003dh / URCA-2, as well as GRB 060218 / SN 2006aj are discussed.

astro-ph↗