Gamma-ray bursts from evaporating primordial black holes

It is believed that the detection of gamma-ray bursts from evaporating primordial black holes is highly improbable in the near future since the expected photon flux, consisting mainly of photons with energies ? GeV, is too low. Contrary to this point of view, we show that a large fraction of the black hole power at the final stage of evaporation (the last 10³ s) can be liberated as a burst of soft γ-ray emission of duration 10^?1–10³ s and luminosity 10²⁸–10³¹ erg/s in the energy range 0.1–1 MeV. According to our calculations of the black hole evaporation rate (within the Standard Model of elementary particles), when the black hole temperature exceeds approximately 10 GeV, the charged particle outflow from a black hole forms a well-defined plasma and can be described in the hydrodynamic approximation. In this case more than half of the rest energy of a black hole can be converted into soft gamma-rays due to the presence of the magnetic field with energy density comparable to that of charged particles. We consider various mechanisms leading to such transformation and estimate their efficiency. It is shown that, at least, some of the gamma-ray bursts detected by BATSE can be associated with evaporating black holes.     

Experimental search for gamma-ray bursts from evaporating primordial black holes

The energy spectra and temporal characteristics of high-energy gamma-ray bursts from evaporating primordial black holes have been calculated using various evaporation models. The currently existing theoretical uncertainties in the shape of the evaporated photon spectrum are discussed. The data from the Andyrchy and Carpet-2 arrays of the Baksan Neutrino Observatory (Institute for Nuclear Research, Russian Academy of Sciences) obtained in the mode of detection of a single cosmic-ray component are used to search for cosmic gamma-ray bursts with a primary photon energy of about 8 GeV. New upper limits have been obtained for the number density of evaporating black holes in a local region of space with a characteristic size of ～10^?3 pc for various evaporation models.     

Constraints on the number density of evaporating primordial black holes for the chromospheric evaporation models

Cosmic gamma-ray bursts with primary-photon energies ≥ 10 GeV are sought in the data from the Andyrchy array obtained in the mode of detection of a single cosmic-ray component during a net observation period of 2005.4 d. The distribution of fluctuations of the detector count rate agrees with the expected cosmic-ray background, the only exception being an event with a deviation of 7.9σ. Constraints on the number density of evaporating primordial black holes in a local region of the Galaxy are obtained for the chromospheric evaporation models.     

Quantum Tunneling of Dirac Particles from?the?Generalized Spherical Symmetric Evaporating Charged Black Hole

Kerner and Mann’s recent research shows that, for an uncharged and non-rotating black hole, its Hawking temperature and tunneling rate can be exactly obtained by the fermion tunneling method from its event horizon. In this paper, considering the tunneling charged particles with spin 1/2, we extend Kerner and Mann’s method to the generalized spherical symmetric evaporating charged black hole which is non-stationary. In order to investigate the fermion tunneling through the event horizon, we choose a set of appropriate matrices γ ^μ . As a result, the tunneling probability and truly effective temperature are well recovered by charged fermions tunneling from the black hole.     

Search for cosmic γ-ray bursts in the (1÷50) GeV energy range

Summary A search for cosmic gamma-ray bursts in the GeV energy range has been performed by means of the EAS-TOP Extensive Air Shower array at Campo Imperatore (Gran Sasso Laboratories) during the period March–December 1990. In 2566.5 hours of measurement the obtained upper limit to the rate of bursts of amplitude >2% of the cosmic-ray intensity and time duration τ=1 s, isR≤7.9y⁻¹ (90% c.l.). Assuming for γ-rays a differential energy spectrumS(E ₀ )≈E ₀ ^−2.5 , the corresponding upper limit to the energy flux of γ-rays with energy >5 GeV in bursts of duration τ≤1 s is Φ<8.3·10⁻⁵erg cm⁻².     

Cosmological γ-ray bursts from a neutron star collapse induced by a primordial black hole

A detailed analysis is presented for a novel scenario in which gamma-ray bursts are of intergalactic origin and arise from the induced collapse of an isolated neutron star triggered by a primordial black hole. The energy released from the phase transition of accreted nucleon matter into a quark-gluon plasma is transferred by degenerate neutrinos to the star’s surface, where neutrinos annihilate into an electron-positron plasma and produce an inverted temperature layer that preserves a fire-ball from undue baryonic pollution. Possible observational tests include the absence of apparent cosmological time dilation, the location of γ-ray bursts primarily outside of galaxies, a specific shape of the log N-log S curve, with a large peak near red shift z∼10, the emission of ∼10⁻³ of the total energy in the form of 100-GeV photons, a bimodal distribution of durations, a very weak accompanying pulse of gravitational radiation, etc. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 10, 642–647 (25 November 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Phantom energy accretion and primordial black holes evolution in Brans–Dicke theory

In this work, we study the evolution of primordial black holes within the context of Brans–Dicke theory by considering the presence of a dark energy component with a super-negative equation of state, called phantom energy, as a background. Besides Hawking evaporation, here we consider two types of accretion—radiation accretion and phantom energy accretion. We found that radiation accretion increases the lifetime of primordial black holes whereas phantom accretion decreases the lifespan of primordial black holes. Investigating the competition between the radiation accretion and phantom accretion, we found that there is an instant during the matter-dominated era beyond which phantom accretion dominates radiation accretion. So the primordial black holes which are formed in the later part of radiation-dominated era and in matter-dominated era are evaporated at a quicker rate than by Hawking evaporation. But for presently evaporating primordial black holes, radiation accretion and Hawking evaporation terms are dominant over the phantom accretion term and hence presently evaporating primordial black holes are not much affected by phantom accretion.     

Bound on induced gravitational wave background from primordial black holes

The today’s energy density of the induced (second order) gravitational wave background in the frequency region ∼10⁻³–10³ Hz is constrained using the existing limits on primordial black hole production in the early Universe. It is shown, in particular, that at frequencies near ∼40 Hz (which is the region explored by LIGO detector), the value of the induced part of Ω_GW cannot exceed (1−3) × 10⁻⁷. The spread of values of the bound is caused by the uncertainty in parameters of the gravitational collapse of black holes.     

Particle acceleration in Horava–Lifshitz black holes

In this paper we calculate the center-of-mass energy of two colliding test particles near the rotating and non-rotating Horava–Lifshitz black hole. For the case of a slowly rotating KS solution of Horava–Lifshitz black hole we compare our results with the case of Kerr black holes. We confirm the limited value of the center-of-mass energy for static black holes and unlimited value of the center-of-mass energy for rotating black holes. Numerically, we discuss temperature dependence of the center-of-mass energy on the black hole horizon. We obtain the critical angular momentum of particles. In this limit the center-of-mass energy of two colliding particles in the neighborhood of the rotating Horava–Lifshitz black hole could be arbitrarily high. We found appropriate conditions where the critical angular momentum could have an orbit outside the horizon. Finally, we obtain the center-of-mass energy corresponding to this circle orbit.     

Magnetic charge,black holes,and cosmic censorship

The possibility of converting a Reissner-Nordström black hole into a naked singularity by means of test particle accretion is considered. The dually charged Reissner-Nordström metric describes a black hole only when M² > Q³ + P². The test particle equations of motion are shown to allow test particles with arbitrarily large magnetic charge/mass ratios to fall radially into electrically charged black holes. To determine the nature of the final state (black hole or naked singularity) an exact solution of Einstein's equations representing a spherical shell of magnetically charged dust falling into an electrically charged black hole is studied. Naked singularities are never formed so long as the weak energy condition is obeyed by the infalling matter. The differences between the spherical shell model and an infalling point test particle are examined and discussed.     

Scientific tasks and present status of the GAMMA-400 project

The GAMMA-400 telescope is designed to investigate discrete high-energy gamma-ray sources in the energy range of 0.1–3000 GeV, to measure the energy spectra of galactic and extragalactic diffuse gammaray emissions, and to study gamma-ray bursts and gamma-ray emissions from an active Sun. The gamma-ray telescope has an angular resolution of ～0.01°, an energy resolution of ～1%, and a proton rejection factor of ～10⁶. Its special assignment is to measure fluxes of gamma rays, electrons, and positrons that could be associated with the annihilation or decay of dark matter particles.     

Electron-positron outflow from black holes

Cosmological gamma-ray bursts (GRBs) appear as the brightest transient phenomena in the Universe. The nature of their central engine is a missing link in the theory of fireballs to stellar mass progenitors, and may be associated with low mass black holes. In contact with an external magnetic field B, black hole spin produces a gravitational potential on the wave function of charged particles. We show that a rapidly rotating black hole of mass M produces outflow from initially electrostatic equilibrium with normalized isotropic emission approximately 10(48)(B/B(c))(2)(M/7M)(2)sin (2) theta erg/s, where B(c) = 4.4x10(13) G. The half-opening angle satisfies theta >or = square root[B(c)/3B]. The outflow proposed as input to GRB fireball models.     

Primordial black holes in phantom cosmology

We investigate the effects of accretion of phantom energy onto primordial black holes. Since Hawking radiation and phantom energy accretion contribute to a decrease of the mass of the black hole, the primordial black hole that would be expected to decay now due to the Hawking process would decay earlier due to the inclusion of the phantom energy. Equivalently, to have the primordial black hole decay now it would have to be more massive initially. We find that the effect of the phantom energy is substantial and the black holes decaying now would be much more massive—over ten orders of magnitude! This effect will be relevant for determining the time of production and hence the number of evaporating black holes expected in a universe accelerating due to phantom energy.     

A search for high-energy cosmic gamma-ray bursts

Summary A search has been made for excesses of cosmic-ray counting rates at primary energiesE ₀₁>5 GeV andE ₀₄>2·10⁴ GeV over the time scalet=(1÷100) ms. The measurement was performed by means of a small extensive air shower array operating at mountain altitude (3500 m a.s.l.). During the running time 111 cosmic gamma-ray bursts were detected by satellites; 10 of them certainly (55 probably) above the horizon of the detector. No significant counting rate excess has been recorded out of the statistical fluctuations. Also the search for correlations with satellite events has given a negative result. The upper limit for high-energy cosmic gamma-ray flux in bursts isϕ ₁(E>E ₀₁)<4·10⁻⁵ (t = time scale in ms),ϕ ₄(E>E ₀₄)<1.6·10⁻⁵erg/cm². Paper presented at the 2^o Convegno Nazionale di Fisica Cosmica, held at L'Aquila, 29 May–2 June 1984.     

Characteristics of the GAMMA-400 gamma-ray telescope for searching for dark matter signatures

The GAMMA-400 gamma-ray telescope currently under development is designed to measure fluxes of gamma rays and electron-positron cosmic-ray components, which could be associated with the annihilation or decay of dark matter particles, and to survey in detail the celestial sphere in order to search for and investigate discrete gamma-ray sources; to measure the energy spectra of Galactic and extragalactic dif- fuse gamma-ray emissions; and to study gamma-ray bursts and the gamma-ray emissions of active Sun. The GAMMA-400 energy range is 100 MeV to 3000 GeV. The gamma-ray telescope has an angular resolution of ～0.01°, an energy resolution of ～1%, and a proton rejection factor of ～10⁶. The GAMMA-400 will be installed on Russia’s Navigator space platform. Observations are planned to commence in 2018.     

Hydrodynamic and hydromagnetic stability of black holes with radiative transfer

Subrahmanyan Chandrasekhar (Chandra) was just eight years old when the first astrophysical jet was discovered in M87. Since then, jets have been uncovered with a wide variety of sources including accretion disks orbiting stellar and massive black holes, neutron stars, isolated pulsars, γ-ray bursts, protostars and planetary nebulae. This talk will be primarily concerned with collimated hydromagnetic outflows associated with spinning, massive black holes in active galactic nuclei. Jets exhibit physical processes central to three of the major research themes in Chandrasekhar’s research career – radiative transfer, magnetohydrodynamics and black holes. Relativistic jets can be thought of as ‘exhausts’ from both the hole and its orbiting accretion disk, carrying away the energy liberated by the rotating spacetime and the accreting gas that is not radiated. However, no aspect of jet formation, propagation and radiation can be regarded as understood in detail. The combination of new γ-ray, radio and optical observations together with impressive advances in numerical simulation make this a good time to settle some long-standing debates.     

Gamma-ray direct observations from space

Summary This paper is devoted to problems of gamma-ray astronomy in the energy range <10¹¹ eV. Measurements of spectra and fluxes in this energy range are carried out by means of direct observations from space. Most of the discussed results have been performed with the four telescopes of the Compton Gamma-Ray Observatory. The main topics of the paper are: diffuse galactic gamma-ray emission, point-like galactic gamma-ray sources, gamma-ray line emission, gamma-ray bursts and active galactic nuclei. Rapporteur talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September, 8, 1995.     

On the oscillations of the plasma atmosphere in gamma-ray bursts

One of the possible hypotheses implies that cosmic gamma-ray bursts can arise when two neutron stars or black holes merge together. These bursts sometimes continue for several tens of seconds, but the time dependence of their intensity often exhibits ～10²–10³ almost periodic small peaks with a period of ～10 ms. A model of oscillations in the lower plasma shell, which arises in cosmic gamma-ray bursts and is located near a neutron star, is proposed; the greater part of arising plasma in the form of an “upper” shell continues to expand into the surroundings. Other possible interpretations of periodicity of the “small peaks” are also analyzed.     

Gauss-bonnet black holes and possibilities for their experimental search

Corollaries of gravity models with second-order curvature corrections in the form of a Gauss-Bonnet term and possibilities (or impossibilities) for their experimental search or observations are discussed. The full version of the four-dimensional Schwarzschild-Gauss-Bonnet black hole solution and the constraint on the possible minimal black hole mass following from this model are considered. Using our solution as a model for the final stages of Hawking evaporation of black holes with a low initial mass (up to 10¹⁵ g) whose lifetime is comparable to that of our Universe, we have revealed differences in the patterns of evaporation: we have obtained high values of the emitted energy and showed the impossibility of an experimental search for primordial black holes by their evaporation products. Scenarios for the evaporation of Gauss-Bonnet black holes in multidimensional gravity models and possibilities for their experimental search are also discussed.     

Possible effects of a cosmological constant on black hole evolution

We explore possible effects of vacuum energy on the evolution of black holes. If the universe contains a cosmological constant, and if black holes can absorb energy from the vacuum, then black hole evaporation could be greatly suppressed. For the magnitude of the cosmological constant suggested by current observations, black holes larger than 4×10²⁴ g would accrete energy rather than evaporate. In this scenario, all stellar and supermassive black holes would grow with time until they reach a maximum mass scale of 6×10⁵⁵ g, comparable to the mass contained within the present day cosmological horizon.