Narrow Results

The observation of gravitational waves from the Laser Interferometer Gravitational-Wave Observatory (LIGO) event GW150914 may be used to constrain the possibility of Lorentz violation in graviton propagation, and the observation by the Fermi Gamma-Ray Burst Monitor (GBM) of a transient source in apparent coincidence may be used to constrain the difference between the velocities of light and gravitational waves: $c_g-c_{\gamma }<10^{-17}$.

We investigate the wave effect in the gravitational lensing by a black hole with very tiny mass less than 10^-19 M_sun (solar mass), which is called attolensing, motivated by a recent report that the lensing signature might be a possible probe of a modified gravity theory in the braneworld scenario. We focus on the finite source size effect and the effect of the relative motion of the source to the lens, which are influential to the wave effect in the attolensing. Astrophysical condition that the lensed interference signature can be a probe of the modified gravity theory is demonstrated. The interference signature in the microlensing system is also discussed.

We review the recent progress in understanding the nature of gamma-ray bursts (GRBs). The occurrence of GRB is explained by the Induced Gravitational Collapse (IGC) in FeCO Core–Neutron star binaries and Neutron star–Neutron star binary mergers, both processes occur within binary system progenitors. Making use of this most unexpected new paradigm, with the fundamental implications by the neutron star (NS) critical mass, we find that different initial configurations of binary systems lead to different GRB families with specific new physical predictions confirmed by observations.

A time varying space–time metric is shown to be a source of electromagnetic radiation even in the absence of charge sources. The post-Newtonian approximation is used as a realistic model of the connection between the space–time metric and a time-varying gravitational potential. Rapid temporal variations in the metric from the coalescence of relativistic stars are shown to be likely progenitors of gamma ray burst and millisecond pulsars.

Current research marks a clear success in identifying the moment of formation of a Black Hole of ~ 10M_⊙, with the emission of a Gamma Ray Burst. This explains in terms of the 'Blackholic Energy' the source of the energy of these astrophysical systems. Their energetics up to 10⁵⁴ erg, make them detectable all over our Universe. Concurrently a new problematic has been arising related to: (a) The evidence of Dark Matter in galactic halos; (b) The origin of the Super Massive Black Holes in active galactic nuclei and Quasars and (c) The purported existence of a Black Hole in the Center of our Galaxy. These three aspects of this new problematic have been traditionally approached independently. We propose an unified approach to all three of them based on a system of massive self-gravitating neutrinos in General Relativity. Perspectives of future research are presented.

We review recent progress in our understanding of the nature of Gamma Ray Bursts (GRBs) and in particular, of the relationship between short GRBs and long GRBs. The first example of a short GRB is described. The coincidental occurrence of a GRB with a supernova (SN) is explained within the induced gravitational collapse (IGC) paradigm, following the sequence: (1) an initial binary system consists of a compact carbon–oxygen (CO) core star and a neutron star (NS); (2) the CO core explodes as a SN, and part of the SN ejecta accretes onto the NS which reaches its critical mass and collapses to a black hole (BH) giving rise to a GRB; (3) a new NS is generated by the SN as a remnant. The observational consequences of this scenario are outlined.

We examine the short-term effects that a galactic Gamma Ray Burst would cause on a planetary biosphere. The immediate environmental perturbation would arise due to the emission of an aurora like spectrum in the middle and low atmosphere, delivering at planet's surface a brief but intense ultraviolet flash. We calculated potential damages to both the photosynthetic and DNA apparatuses of unicellular organisms. We conclude that if the progenitor is 1-2 kiloparsec distant in the Milky Way, its main short-term bio-effect will be radiation damage in the photosynthetic machinery rather than in the genome.

We discuss the potential past incidence of a galactic gamma ray burst on Earth. Rough estimates for the relative frequencies of this kind of event are given, for the different eons of our planet's geological history. Additionally, we explore the effectiveness of the ozone layer of different paleo-atmospheres to shield the surface of the planet from the ultraviolet flash, which arises as a short-term effect after the incidence of a galactic gamma ray burst.

In this paper we propose a new plausible mechanism of supernova explosions specific to close binary systems. The starting point is the common envelope phase in the evolution of a binary consisting of a red super giant and a neutron star. As the neutron star spirals towards the center of its companion it spins up via disk accretion. Depending on the specific angular momentum of gas captured by the neutron star via the Bondi-Hoyle mechanism, it may reach millisecond periods either when it is still inside the common envelope or after it has merged with the companion core. The high accretion rate may result in strong differential rotation of the neutron star and generation of a magnetar-strength magnetic field. The magnetar wind can blow away the common envelope if its magnetic field is as strong as 10¹⁵ G, and can destroy the entire companion if it is as strong as 10¹⁶ G. The total explosion energy can be comparable to the rotational energy of a millisecond pulsar and reach 10⁵² erg. The result is an unusual type-II supernova with very high luminosity during the plateau phase, followed by a sharp drop in brightness and a steep light-curve tail. The remnant is either a solitary magnetar or a close binary involving a Wolf-Rayet star and a magnetar. When this Wolf-Rayet star explodes this will be a third supernovae explosion in the same binary. A particularly interesting version of the binary progenitor involves merger of a red super giant star with an ultra-compact companion, neutron star or black hole. In the case if a strong magnetic field is not generated on the surface of a neutron star then it will collapse to a black hole. After that we expect the formation of a very long-lived accretion disk around the black hole. The Blandford-Znajek driven jet from this black hole may drive not only hypernovae explosion but produce a bright X-ray transient event on a time scale of 10⁴ s.

A persistent, thin (a solid angle less than 0.1μsr.), gamma jet, may be ejected from BH and Pulsars, powered by ultra-relativistic electron pairs. These γ jet while precessing and spinning are originated by Inverse Compton⁷ and-or Synchrotron Radiation at pulsars or micro-quasars sources. They are most powerful at Supernova birth blazing, once on axis, to us and flashing GRB detector. The trembling of the thin jet explains naturally the observed erratic multi-explosive structure of different GRBs. The jets are precessing (by binary companion) and decaying on time scales of a few hours but they are usually staying inside the observer cone view only a few seconds (GRB) duration times; the jets whole lifetime, while decaying in output, could survive as long as thousands of years, linking huge GRB-SN jet apparent Luminosity to more modest SGR relic Jets (at corresponding X-Ray pulsar output). Therefore long-life SGR may be repeating and if they are around our galaxy they might be observed again as the few known ones and a few rarer extragalactic XRFs. The orientation of the beam respect to the line of sight plays a key role in differentiating the wide GRB morphology. The relativistic cone is as small as the inverse of the electron progenitor Lorentz factor (γ_e ≃ 10³ – 10⁴ for I.C.⁷ and γ_e ≃ 10⁸ – 10⁹ for Synchrotron radiation). The hardest and brightest gamma spectra are hidden inside the inner gamma jet axis. To observe the inner beamed GRB events one needs the widest SN sample and largest cosmic volumes (red-shift ≥ 1). The most beamed are hardest. On the contrary the nearest ones, within tens Mpc distances, are mostly observable on cone periphery. Their consequent large impact crossing angle, leads to longest anomalous SN-GRB duration, with lowest fluency and the softest spectra, as in GRB060218 signature. A majority of GRB jet blazing much later (weeks, months after) may hide their progenitor explosive SN after-glow and therefore are so called orphan GRB. The late GRBs are called now local SGRs (or in outer extragalactic XRF) and are linked to anomalous X-ray AXPs. Conical shape of few nebulae and the precessing jet of few known micro-quasar describe in space the model 3D signature. Recent outstanding episode of X-ray precursor, ten minutes before the main GRB event, cannot be understood otherwise.

MAGIC is presently the imaging atmospheric Cherenkov telescope with the largest reflecting surface and the lowest energy threshold. MAGIC concluded its first year of regular observation in April 2006. During this period and the preceding commissioning phase, several Gamma-Ray Bursts were observed by the MAGIC telescope thanks to its very fast slewing capabilities. The observations were triggered by GCN alerts received from SWIFT, HETE2 and INTEGRAL satellites and were performed various minutes following the alert. The threshold energies depend on the zenith angle of the burst location and span between 80 GeV and 200 GeV. Using standard MAGIC analysis, no evidence of gamma signals was found.

In this work we describe the results of our numerical study on the possibility of magnetic origin of relativistic jets of long duration gamma ray bursts within the collapsar scenario which is expansion of works Barkov & Komissarov.¹⁻³ We track the collapse of massive rotating stars onto a rotating central black hole using axisymmetric general relativistic magnetohydrodynamic code that utilizes a realistic equation of state of stellar matter, takes into account the cooling associated with emission of neutrinos, and the energy losses due to dissociation of nuclei. The neutrino heating is not included. We describe the solutions for several models where the progenitor star has magnetic field from B = 3 × 10¹⁰G to B = 3 × 10⁹G, for different envelop accretion rates, black hole rotation parameter a and specific angular momentum of the stellar envelop. The some solution exhibits strong explosion driven by the Poynting-dominated jets whose power exceeds up to 12 × 10⁵¹ erg s⁻¹. The criterion for explosion were derived. The jets originate mainly from the black hole and they are powered via the Blandford-Znajek mechanism.

One of the least documented and understood aspects of gamma-ray bursts (GRB) is the rise phase of the optical light curve. The Ultra-Fast Flash Observatory (UFFO) is an effort to address this question through extraordinary opportunities presented by a series of space missions including a small spacecraft observatory. The UFFO is equipped with a fast-response Slewing Mirror Telescope (SMT) which uses rapidly moving mirror or mirror arrays to redirect the optical beam rather than slewing the entire spacecraft to aim the optical instrument at the GRB position. The UFFO will probe the early optical rise of GRBs with a sub-second response, for the first time, opening a completely new frontier in GRB and transient studies, the only GRB system which can point and measure on these time scales. Its fast response measurements of the optical emission of dozens of GRB each year will provide unique probes of the burst mechanism, shock breakouts in core-collapse supernovae, tidal disruptions around black holes, test Lorentz violation, be the electromagnetic counterpart to neutrino and gravitational wave signatures of the violent universe, and verify the prospect of GRB as a new standard candle potentially opening up the z>10 universe. As a first step, we employ a motorized slewing stage in SMT which can point to the event within 1s after X-ray trigger, in the UFFO-pathfinder payload onboard the Lomonosov satellite to be launched in 2012. The pathfinder was a small and limited, yet remarkably powerful micro-observatory for rapid optical response to bright gamma-ray bursts, the first part of our GRB and rapid-response long-term program. We describe the early photon science, the space mission of UFFO-pathfinder, and our plan for the next step.