We consider a scenario for the longest duration gamma ray bursts, resulting from the collapse of a massive star in a close binary system with a companion black hole. The primary black hole born during the core collapse is spun up and increases its ma
ss during the fallback of the stellar envelope. The companion black hole provides an additional angular momentum to the envelope, which ultimately makes the core BH spinning with a high Kerr parameter. After the infall and spiral-in, the two black holes merge inside the circumbinary disk. The second episode of mass accretion and final, even larger spin of the post-merger black hole prolongs the gamma ray burst central engine activity. The observed events should have two distinct peaks in the electromagnetic signal, separated by the gravitational wave emission. The gravitational recoil of the burst engine is also possible.
Gamma Ray Bursts (GRB) are the extremely energetic transient events, visible from the most distant parts of the Universe. They are most likely powered by accretion on the hyper-Eddington rates that proceeds onto a newly born stellar mass black hole.
This central engine gives rise to the most powerful, high Lorentz factor jets that are responsible for energetic gamma ray emission. We investigate the accretion flow evolution in GRB central engine, using the 2D MHD simulations in General Relativity. We compute the structure and evolution of the extremely hot and dense torus accreting onto the fast spinning black hole, which launches the magnetized jets. We calculate the chemical structure of the disk and account for neutrino cooling. Our preliminary runs apply to the short GRB case (remnant torus accreted after NS-NS or NS-BH merger). We estimate the neutrino luminosity of such an event for chosen disk and central BH mass
We discuss two important instability mechanisms that may lead to the limit-cycle oscillations of the luminosity of the accretion disks around compact objects: ionization instability and radiation-pressure instability. Ionization instability is well e
stablished as a mechanism of X-ray novae eruptions in black hole binary systems but its applicability to AGN is still problematic. Radiation pressure theory has still very weak observational background in any of these sources. In the present paper we attempt to confront the parameter space of these instabilities with the observational data. At the basis of this simple survey of sources properties we argue that the radiation pressure instability is likely to be present in several Galactic sources with the Eddington ratios above 0.15, and in AGN with the Eddington ratio above 0.025. Our results favor the parameterization of the viscosity through the geometrical mean of the radiation and gas pressure both in Galactic sources and AGN. More examples of the quasi-regular outbursts in the timescales of 100 seconds in Galactic sources, and hundreds of years in AGN are needed to formulate firm conclusions. We also show that the disk sizes in the X-ray novae are consistent with the ionization instability. This instability may also considerably influence the lifetime cycle and overall complexity in the supermassive black hole environment.
We formulate a complete microscopic theory of a coupled pair of bound magnetic polarons, the bound-magnetic-polaron molecule (BMPM) in a diluted magnetic semiconductor (DMS) by taking into account both a proper two-body nature of the impurity-electro
n wave function and within the general spin-rotation-invariant approach to the electronic states. We also take into account both the Heisenberg and the antiferromagnetic kinetic-exchange interactions, as well as the ferromagnetic coupling within the common spin BMPM cloud. The thermodynamic fluctuations of the spin cloud within the polaron effective Bohr radius of each polaron are taken as Gaussian.
With the plethora of detailed results from heliospheric missions and at the advent of the first mission dedicated IBEX, we have entered the era of precision heliospheric studies. Interpretation of these data require precision modeling, with second-or
der effects quantitatively taken into account. We study the influence of the non-flat shape of the solar Ly-alpha line on the distribution of neutral interstellar H in the inner heliosphere. Based on available data, we (i) construct a model of evolution for the solar Ly-alpha line profile with solar activity, (ii) modify an existing test-particle code used to calculate the distribution of neutral interstellar H in the inner heliosphere so that it takes the dependence of radiation pressure on radial velocity into account, and (iii) compare the results of the old and new version. Discrepancies between the classical and Doppler models appear between ~5 and ~3 AU and increase towards the Sun from a few percent to a factor of 1.5 at 1 AU. The classical model overestimates the density everywhere except for a ~60-degr cone around the downwind direction, where a density deficit appears. The magnitude of the discrepancies appreciably depends on the phase of the solar cycle, but only weakly on the parameters of the gas at the termination shock. For in situ measurements of neutral atoms performed at ~1 AU, the Doppler correction will need to be taken into account, because the modifications include both the magnitude and direction of the local flux by a few km/s and degrees, respectively, which, when unaccounted for, would introduce an error of a few km/s and degrees in determination of the magnitude and direction of the bulk velocity vector at the termination shock.
We discuss causality properties of extra-dimensional theories allowing for effectively superluminal bulk shortcuts. Such shortcuts for sterile neutrinos have been discussed as a solution to the puzzling LSND and MiniBooNE neutrino oscillation results
. We focus here on the sub-category of asymmetrically warped brane spacetimes and argue that scenarios with two extra dimensions may allow for timelike curves which can be closed via paths in the extra-dimensional bulk. In principle sterile neutrinos propagating in the extra dimension may be manipulated in a way to test the chronology protection conjecture experimentally.
