Gamma ray modulation in AGN by interaction with X�rays from an accretion disk hot spot W. Bednarek interactions with X�rays emitted by a hot spot in the inner part of the accretion disk. As the hot spot orbits originates in a relatively small hot spot rotating on the ...

jets that produce gamma-ray bursts. I will present time-dependent calculations of the evolution of hyper-accreting disks as they accrete onto the central NS or BH and spread...

Context. We study the precession of accretion disks in the context of gamma-ray burst inner engines. Aims: Our aim is to quantitatively estimate the characteristics of gravitational waves produced by the precession of the transient accretion disk in gamma-ray bursts. Methods: We evaluate the possible periods of ...

Context. Recently observed rapid time variability in the gamma ray emission from the blazar PKS 2155-304 indicates that either the site of gamma ray emission is close to the black hole or the jet has a very high Lorentz factor. Consideration of the opacity of gamma rays ...

We study proton-rich nucleosynthesis in windlike outflows from {gamma}-ray bursts accretion disks with the aim of determining if such outflows are a site of the nup process. The efficacy of this nup process depends on thermodynamic and hydrodynamic factors. We discuss the importance of the entropy of the material, the outflow rate, the ...

The inner regions of accretion disks of supermassive black holes can become unstable when the existing temperatures are sufficiently high. This naturally occurs for two-temperature disks in the case of rapidly spinning (Kerr) black holes. Physical effects...

The spectrum of Gamma rays from the decay of Pi dey is sensitive to the ... X- Ray Reflected Spectra from Accretion Disk Models. II. Diagnostic Tools for X-Ray ... This study demonstrates the ability of the model to generate recurrent 3D ...

Results 51 - 75 ... Gamma-rays, more than 10 8 Kelvin (K), accretion disks around black holes. X- rays, 10 6 -10 8 K, gas in clusters of galaxies; ...

Gamma-ray bursts, while rare, may be important contributors to galactic nucleosynthesis. Here we consider the types of nucleosynthesis that can occur as material is ejected from a gamma-ray burst accretion disk. We calculate the composition of material within the disk as it dissociates into protons and neutrons and ...

Hot accretion disks around rotating black holes produce copious amounts of X-rays, ..gamma..-rays and e/sup +/e/sup -/ pairs. These Comptonized models with an energy flux spectral index of the X-ray spectrum approx. 1 are optically thick to ..gamma gamma.. pair production. The resultant high energy spectrum steepens above a few MeV. ...

Context. The microquasar Cygnus X-3 was detected at high energies by the gamma-ray space telescopes AGILE and Fermi. The gamma-ray emission is transient, modulated with the orbital period and seems related to major radio flares, i.e. to the relativistic jet. The GeV gamma-ray flux can be substantially attenuated by internal absorption with the ambient X-rays. Aims: We examine ...

We propose a simple model for the gamma-ray bursts based on high- velocity Galactic neutron stars that have accretion disks. The latter are formed from a mixture of material from the supernova shell and that ablated from a pre-supernova binary companion. Accretion onto the neutron star from this disk when the ...

Several types of cataclysmic events involving stellar-mass compact objects could result in the extreme, transient accretion onto a black hole widely believed to power gamma-ray bursts. We calculate the vertical structure of such thick accretion disks with a semi-analytical model which includes the effects of ...

We examine the nucleosynthesis products that are produced in the outflow from rapidly accreting disks. We find that the type of element synthesis varies dramatically with the degree of neutrino trapping in the disk and therefore the accretion rate of the disk. Disks with ...

We examine the nucleosynthesis products that are produced in the outflow from rapidly accreting disks. We find that the type of element synthesis varies dramatically with the degree of neutrino trapping in the disk and therefore the accretion rate of the disk. Disks with ...

Accretion in astrophysical objects and the energetic phenomena it triggers are discussed in reviews and reports of recent theoretical and observational investigations. Topics examined include fly's-eye observations of ultrahigh-energy (UHE) gamma rays, recent results from the IMB detector, the theoretical implications of UHE detections ...

Light curves from a growing number of Gamma Ray Bursts (GRBs) indicate that GRBs copiously produce radioactive Ni moving outward at fractions of the speed of light. We calculate nuclear abundances of elements accompanying the outflowing Ni under the assumption that this Ni originates from a wind blown off of a viscous accretion ...

A signal (chance probability = 2 x 10/sup -4/) with a 1.24 s period has been observed from the direction of Hercules H-1. The signal's relatively long period and high shower energy conflict with some popular models of particle acceleration by pulsars. Optical and X-ray data support our picture in which energetic particles produce multi--TeV ..gamma..-rays by ...

We propose a Galactic model for the isotropic component of gamma-my bursts (GB`s) based upon high-velocity neutron stars (NS`s) that have accretion disks. The fast NS`s are formed in tidally locked binaries, leading to a unique fast NS population. The tidal locking occurs due to the meridional circulation caused by the conservation of angular momentum of ...

The authors suggest that a rotating massive black hole (105Msun) located at an inactive galaxy may convert its host into a transient active phase by capturing and disrupting a star. During this period, a transient accretion disk is formed and a strong transient magnetic field can be produced in the inner boundary of the accretion ...

We investigate nucleosynthesis inside both a gamma-ray burst accretion disk and a wind launched from an inner region of the disk using one-dimensional models of the disk and wind and a nuclear reaction network. Far from a central black hole, the composition of accreting gas is taken to be that ...

The nuclear ..gamma..-ray lines in the emission spectrum of the nucleus of the active galaxy Cen A imply that the object contains a source of protons with energies of several tens of MeV. The total energy of the protons in the source is estimated.

The suggestion was first made more than a year ago that gamma-ray bursts might originate in the neighborhood of black holes, based on some rather circumstantial evidence linking Cygnus X-1, the prime black-hole candidate, with two of the then-known gamma-...

The importance for future high-energy astrophysics space missions to incoporate the study of gamma emission from black hole candidates as a major component their scientific goals is discussed. Such gamma emission can provide excellent diagnostics for black hole astrophysics and is particularly sensitivity to the accretion disk phenomena. (AIP)

It is proposed a new mechanism for high energy gamma ray burst in Supernova type I (SNI) explosion. Presupernova is assumed to be a binary system comprised of a red giant and a white dwarf with a wind accretion. The accretion flow terminates by the accret...

The rotation rate in pre-supernova cores is an important ingredient that can profoundly affect the post-collapse evolution and associated energy release in supernovae and long gamma ray bursts (LGRBs). Previous work has focused on whether the specific angular momentum is above or below the critical value required for the creation of a centrifugally ...

We consider the long-term evolution of debris following the tidal disruption of compact stars in the context of short gamma ray bursts. The initial encounter impulsively creates a hot, dense, neutrino-cooled disk capable of powering the prompt emission. After a long delay, we find that powerful winds are launched from the surface of ...

Gamma ray data favor a cosmic ray propagation halo comparable with the thickness of the primary radio emission disk of our Galaxy and the halo seen around NGC891.

We explore models for the diffuse cosmic X-ray and gamma ray backgrounds. We show that hot gas (T approx. equals 4 x 108 K cannot explain the X-ray background, whether it is smoothly distributed or confined in clumps, because of its effects on the cosmic microwave background and on the images of quasars. We show that active galactic nuclei (AGN), whose ...

The HEAO-3 data for the enhanced MeV gamma ray emissions of Cygnus X-1 and the Galactic Center in 1979 can be modeled by thermal emissions from a compact pair-dominated cloud surrounding the black hole. We derive from first principles the structure of such pair clouds and use these results to constrain the mass of the central black hole, the viscosity ...

The standard massive accretion disk with Keplerian angular momentum (standard accretion disk) producing gamma-ray bursts (GRBs) is investigated on the bases of the microphysics of neutrinos and general relativity. Since the accretion disk gradually ...

The standard massive accretion disk with Keplerian angular momentum (standard accretion disk) producing gamma-ray bursts (GRBs) is investigated on the bases of the microphysics of neutrinos and general relativity. Since the accretion disk gradually ...

This work discusses a black hole accretion disk dynamo model for Active Galactic Nuclei (AGN) sources of the cosmic X-ray and ..gamma.. ray backgrounds which involves both thermal and nonthermal accretion disk processes around greater than or equal to 10/sup 8/M/sub sun/ ...

Observational evidence suggests long-duration, collapsar-type gamma-ray bursts (GRBs) may have been more common in the early universe. These events are thought to be powered by accretion disks around black holes (AD-BHs). While GRBs require AD-BHs, not all AD-BHs will power bursts and therefore their formation will be more common than ...

While it is well known that neutrinos are emitted from standard core collapse protoneutron star supernovae, less attention has been focused on neutrinos from accretion disks. These disks occur in some supernovae (i.e. collapsars) as well as in compact object mergers, and they emit neutrinos with similar properties to those from ...

accretion disks in the western Gulf region (Texas and Louisiana). Accretion ... protostellar disks are believed to be accretion disks associated with young, ...

The observational consequences of the reprocessing of gamma-ray burst (GRB) photons by an accretion disk surrounding a neutron star are explored. Reprocessing of gamma rays by cold disks driven by dynamical viscosity of nonrelativistic, degenerate electrons results in an optical/UV fluence ...

The observational consequences of the reprocessing of gamma-ray burst (GRB) photons by an accretion disk surrounding a neutron star are explored. Reprocessing of gamma rays by cold disks driven by dynamical viscosity of nonrelativistic, degenerate electrons results in an optical/UV fluence ...

In this letter we show that the observed gamma -ray luminosity can be produced by an accretion disc around a non-magnetic neutron star or low mass black hole in which the dominant dissipative process in the disc is due to magnetic fields. The shearing mot...

The current generation of gamma-ray telescopes (SIGMA, GRO) provides a new opportunity for observing

A conference on the energization of charged particles by nonthermal processes throughout the universe produced papers in the areas of the interplanetary medium, solar flares, stars, pulsars, supernovae, supernova remnants, gamma ray bursts, active galaxies, quasars, accretion disks, particle acceleration, and ...

Aims: We report on the third phase of our study of the neutrino-cooled hyperaccreting torus around a black hole that powers the jet in gamma ray bursts. We focus on the influence of the black hole spin on the properties of the torus. Methods: The structure of a stationary torus around the Kerr black hole is solved numerically. We take into account the ...

The high-redshift (z = 4.048) gamma-ray burst GRB 060206 showed unusual behavior, with a significant re-brightening about 3000 s after the burst. We assume that the central engine became active again 2000 s after the main burst and drove another more collimated off-axis jet. The two jets both interacted with the ambient medium and contributed to the whole emission. We ...

Observational evidence suggests a link between long duration gamma ray bursts (LGRBs) and Type Ic supernovae. Here, we propose a potential mechanism for Type Ic supernovae in LGRB progenitors powered solely by accretion energy. We present spherically-symmetric hydrodynamic simulations of the long-term accretion of ...

What makes a Galacic model of gamma-ray bursts (GBs) feasible is the observation of a new population of objects, fast neutron stars, that are isotropic with respect to the Galaxy following a finite period, {approximately}30My, after their formation. Our Galactic model for the isotropic component of (GBs) is based upon these high-velocity neutron stars (NSs) that have accretion ...

... gamma rays from the decay of isotopes produced by ... high-energy protons on the aluminum of the ... be explained by accretion of the isotope onto the ...

Observations of T Tauri stars and young brown dwarfs suggest that the accretion rates of their disks

We calculate the structure of an effectively optically thin and geometrically thin accretion disk in

A model for disk accretion by a rotating magnetic neutron star is proposed which includes a detailed

accretion? " What is the structure of the inner disk? " How do accretion disks drive jets? ... IXO will reveal the physics of disk accretion, and low L_X ...

It has been recognized long ago that the presence of hot plasma in the inner accretion disks around black holes could lead to the neutron production via dissociation of helium nuclei. We show that, for a broad range of accretion parameters, neutrons effectively decouple from protons and pile up in the inner disk ...

The energetics of a ..gamma..-ray burster can be explained by the rapid accretion of > or approx. =10/sup 19/ g of matter onto a neutron star surface. It is proposed that this sudden infall of matter may be the result of a radiation-driven instability which occurs at the boundary between an accretion disk and the surface of a slowly ...

Gamma-ray observations of active galaxies have important consequences for theories of the activity in their nuclei. The observations of Cen A, 3C 273, and NGC 4151 are examined under the assumption that Penrose collision processes in the ergospheres of massive black holes power their nuclei. The observed sharp break in the MeV region of the NGC 4151 spectrum cannot be due to ...

The identification of an echo of reflected radiation in time histories of gamma-ray burst spectra can provide important information about the existence of binary companions or accretion disks in gamma-ray burst systems. Because of the nature of Compton scattering, the spectrum of the echo will be attenuated at gamma-ray energies compared with the spectrum ...

Anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) are magnetar candidates, i.e., neutron stars powered by a strong magnetic field. If they are indeed magnetars, they will emit high-energy gamma rays that are detectable by the Fermi Large Area Telescope (LAT), according to the outer gap model. However, no significant ...

Both types of long and short gamma ray bursts involve a stage of a hyper-Eddington accretion of hot and dense plasma torus onto a newly born black hole. The prompt gamma ray emission originates in jets at some distance from this `central engine' and in most events is rapidly variable, having a ...

Recent observational and theoretical investigations in astrophysics and cosmology are discussed in a collection of review essays. Topics addressed include the early universe, superstring theory, quantum gravity, gravitational radiation, the cosmic microwave background, the age of the universe, accretion disks in AGN, superconducting cosmic strings, nascent ...

Several issues regarding the Blandford-Znajek process are discussed to demonstrate that it can be an effective mechanism for powering gamma-ray bursts. Using a simple circuit analysis, it is argued that the disk power increases the effective power of the black hole accretion disk system, although a part of the ...

Oct 6, 2003... Scintillating Optical Fiber Calorimeter (SOFCal) � Solar Disk Sextant � Tracking and Imaging Gamma Ray Experiment (TIGRE) ...

Ionized matter falling onto an isolated, rotating black hole will be heated sufficiently that proton-proton collisions will produce mesons, including neutral pions, which decay into gamma rays. For massive (1000 M sub circled dot), black holes, the result...

The Burst and Transient Source Experiment (BATSE) on board the Compton Gamma Ray Observatory (CGRO) monitored the entire sky from 1991-2000. I will review highlights of BATSE observations including gamma ray bursts, black hole candidates, accreting pulsar...

Lu Ye, TP-02. A Possible Energy Mechanism for Cosmological Gamma-ray Bursts ... Hyper-Eddington Accretion and Collimated Outflow from Black Holes ...

High Energy Astrophysics: Accretion Disks II 1/59 Accretion Disks II 1 The dynamical equations Astrophysics: Accretion Disks II 2/59 The simplest accretion disc model to construct is that of the thin disc on the azimuthal angle z #12;High Energy ...

Gamma-ray production from the decay of pi(0) mesons deriving from proton-proton interactions in a thermal plasma around a rotating black hole is considered. The temperature and density profile of the accreting plasma are calculated for an adiabatic flow in a Kerr metric with detached electron and proton populations and using the geodesic approximation. The ...

Diffuse Galactic 1.809 MeV line emission, produced by the decay of the radionuclide Al-26 is modeled for nova distributions. Two distinct nova contributions were investigated: accreting carbon-oxygen white dwarfs and accreting oxygen-neon-magnesium white dwarfs. It is demonstrated that the modeled diffuse emissions, as functions of Galactic longitude, are ...

The power carried by the jet of blazars is large, compared to the luminosity produced by their accretion disk, and is probably in the form of kinetic energy of a normal electron-proton plasma. The Poynting flux is modest, as suggested by the inconspicuous synchrotron luminosity when compared to the high energy (hard X-rays and gamma ...

Data from the Fermi-LAT reveal two large gamma-ray bubbles, extending 50� above and below the Galactic center (GC), with a width of about 40� in longitude. The gamma-ray emission associated with these bubbles has a significantly harder spectrum (dN/dE ~ E -2) than the inverse Compton emission from electrons in the Galactic disk, or the ...

data yield the accretion disk thickness, diameter, electron density, and magnetic field. Introduction. The structure of AGN accretion disks on sub-parsec ...

The structure of AGN accretion disks on sub-parsec scales can be probed t,hrough ... GHz to map absorption caused by an inner accretion disk. ...

Nov 19, 2004 ... In an accretion disk, material near the outside moves slower than ... Depending on the angle at which we observe the accretion disk, ...

Jan 29, 2010 ... KY Relativistic Accretion Disk models. A set of models from Dovciak et al. (2004 ) for accretion disk spectra in the strong gravity regime. ...

do not have accretion disks. Optical spectra are the only way that we can .... inner accretion disks) confirms the asymmetrical distribution of such stars ...

Sep 27, 2002 ... Accretion Disk Simulation ... Instead, the graphic shows spiral shock waves in a three dimensional simulation of an accretion disk -- material ...

The blazar 3C 454.3 has been in an historically active state for the last several years. Since the launch of the Fermi Gamma ray Space Telescope, the blazar has undergone several flaring episodes, becoming the brightest persistent source in the gamma ray sky in December 2009. We have carried out an optical and ...

High Energy Astrophysics: Accretion Disks I 1/60 Accretion Disks I References: Accretion Power in Astrophysics, J. Frank, A. King and D. Raine. High Energy Astrophysics, Vol. 2, M.S. Longair, Cambridge Astrophysics: Accretion Disks I 2/60 1 Overview ...

The accretion process onto spinning objects in Kerr spacetimes is studied with numerical simulations. Our results show that accretion onto compact objects with Kerr parameter (characterizing the spin) |a|<M and |a|>M is very different. In the superspinning case, for |a| moderately larger than M, the accretion onto the ...

We study accretion-induced collapse of magnetized white dwarfs as an origin of millisecond pulsars. We apply magnetized accretion disk models to the precollapse accreting magnetic white dwarfs and calculate the white dwarf spin evolution. If the pulsar magnetic field results solely from the flux-frozen fossil white ...

The nature of cosmic gamma ray burst is studied. The sources of the observed gamma bursts are supposed to be presented by the two populations of galactic objects, namely: the old neutron stars concentrated in the galactic disk; and the old degenerated dwa...

gamma-ray flare was much more intense the second time it plunged through the disk. Astronomers don't yet know why. (Credit: NASA's Goddard Space Flight Center, Conceptual Image...

In this work we estimate the accretion-disk mass in the specific scenario of binary-neutron-star-merger with current observational data. Assuming that the outflows of short Gamma-ray Bursts (GRBs) are driven via neutrino-antineutrino annihilation we estimate the disk mass of about half of short bursts in the sample to be $\\sim ...

In this work, we estimate the accretion-disk mass in the specific scenario of binary-neutron-star merger with current observational data. Assuming that the outflows of short gamma-ray bursts (GRBs) are driven via neutrino-antineutrino annihilation we estimate the disk mass of about half of short bursts in the sample to be ~0.01-0.1 M ...

What makes a Galactic model of gamma-ray bursts (GBs) feasible is the observation of a new population of objects, fast neutron stars, that are isotropic with respect to the galaxy following a finite period, {approx}30 My, after their formation (1). Our Galactic model for the isotropic component of GBs is based upon high-velocity neutron stars (NSs) that have accretion ...

Disks, Accretion. USE. ACCRETION DISKS. Disks, Optical. USE. VIDEO DISKS. Disposal (In Space), Hazardous Material. USE. HAZARDOUS MATERIAL DISPOSAL (IN ...

A disk model with gas pressure viscosity. The spectrum from an accretion disk ... viscosity scales as the gas pressure. From Stella and Rosner 1984, ApJ, ...

An analytical model for the accretion of matter onto a collapsed, massive object is employed to calculate the resulting gamma ray emissions and their origins. The accreting gas is assumed to be a fully ionized plasma featuring Maxwellian electron and proton momentum distributions, an isotropic angular distribution ...

E~B still and energy carried by Poynting flux ~ B2c. Center of momentum frame moves relativistically. " Need equipartition particle pressure along axis to ...

BATSE Bright Source Monitor (Pulsed Sources). Frequency & Flux Histories ... 20 transient accreting X-ray binaries since the beginning of the CGRO mission, ...

We study the evolution in axisymmetry of accretion disks formed self-consistently through collapse of magnetized hypermassive neutron stars to black holes. Such stars can arise following the merger of binary neutron stars. They are differentially rotating, dynamically stable, and have rest masses exceeding the mass limit for uniform rotation. However, ...

Ionized matter falling onto an isolated, rotating black hole will be heated sufficiently that proton-proton collisions will produce mesons, including neutral pions, which decay into gamma rays. For massive (1000 M/sub sun/) back holes, the resulting gamma-ray luminosity may exceed 10/sup 36/ erg/s, with a spectrum peaked near 20 MeV.

The purpose of the two-day Workshop on Physics of Accretion Disks Around Compact and Young Stars was

Equations for the structure and appearance of supercritical accretion disks and the radiation-driven

An effort is made to observationally constrain accretion disks on the basis of light curves from the

A possible accretion model associated with the ionization instability of quasar disks is proposed to

The observational consequences of the merger scenario for massive star formation are explored and contrasted with the gradual accumulation of mass by accretion. In high-density protostar clusters, envelopes and disks provide a viscous medium that can dissipate the kinetic energy of passing stars, greatly enhancing the probability of capture. Protostellar ...

The detection of Cyg X-1, PSR B1259-63, LS 5039 and LS I +61 303 at TeV energies have established X-ray binaries as a new class of VHE gamma-ray emitters. In this work, we report results from gamma-ray and X-ray observations of 1A035+262 during a major outburst in December 2009. The TeV gamma-ray data were obtained with VERITAS (0.1-30 ...

There are the two common candidates as the viable energy source for the central engine of long gamma-ray bursts (GRBs) and hypernovae (HNe), neutrino annihilation and magnetic fields. We investigate gravitational wave (GW) emission accompanied by these two mechanisms. Especially, we focus on GW signals produced by neutrinos from a hyper-accreting ...

Data from the Fermi-LAT reveal two large gamma-ray bubbles, extending 50 degrees above and below the Galactic center, with a width of about 40 degrees in longitude. The gamma-ray emission associated with these bubbles has a significantly harder spectrum (dN/dE E^{-2}) than the IC emission from electrons in the Galactic disk, or the gamma-rays produced by ...

A collapsar is a massive rotating star (M_ms > 25 M_sun) whose core collapses to form a black hole. In a rapidly rotating star, the accretion of the rest of the star into the newly-formed black hole produces an energetic long-duration gamma-ray burst (GRB) accompanied by a Type Ib/c supernova. An accretion disk ...

Nov 6, 2000 ... "accretion" means collecting of additional material. Two major places where astronomers see accretion disks are in binary star systems (two ...

Sep 4, 1998 ... 3. Formation of an Accretion Disk. Bonnet-Bidaud and van der Klis (1979) showed that even if the accretion is from the stellar wind, ...

We propose to continue tests of magnetospheric models for sub-Hz quasi-periodic oscillations (QPOs) by completing a series of brief pointed observations of the disk-fed X-ray pulsar Cen X-3 that began in cycle 1. A key test of such models is the comparison of the QPO frequencies observed when the pulsar is spinning up and when it is spinning down. We will use the BATSE all-sky ...

A model is proposed for physical processes that would operate at the galactic center and produce both the 511-keV annihilation line and the ..gamma..-ray continuum. A directive beam of hard (roughly-equal100 MeV) photons would originate near a rotating, supermassive black hole surrounded by a gaseous accretion disk with a magnetic field. This ..gamma..-ray ...

Within the next few years gravitational waves (GWs) from merging black holes (BHs) and neutron stars (NSs) may be directly detected, making a thorough theoretical understanding of these systems a high priority. As an additional motivation, these systems may represent a subset of short-duration gamma-ray burst progenitors. BH-NS mergers are expected to result from primordial, ...

Using a Monte Carlo method an approximation was derived to the Green function for the Compton reflection of relativistic photon h nu greater than about m(e) c-sq, by cold electrons, extending previous treatments of this problem for nonrelativistic photons. In Compton reflection, an external flux of photons impinges upon a semiinfinite slab of electrons, gives a portion of its energy to the ...

I show that the assumption that the acceleration and collimation mechanisms of jets are the same in all the classes of astrophysical objects which are observed to produce jets, can lead to interesting conclusions. Jets have now been observed in: active galactic nuclei, young stellar objects, massive x-ray binaries, low mass x-ray binaries, black hole x-ray transients, ...

Context: The observation of rapidly variable very high energy (VHE) gamma-rays from non-aligned active galactic nuclei (AGNs), as reported from M 87, proves challenging for conventional theoretical acceleration and emission models. Aims: Motivated by recent work on pulsar-type particle acceleration in M 87 (Neronov & Aharonian 2007, ApJ, 671, 85), we re-examine the ...

Data collected by the low-energy detectors of the Hard X-Ray and Low Energy Gamma-Ray Experiment on HEAO 1 were analyzed to study the variability in the temporal behavior of Hercules X-1. Data obtained during thirteen pointed observations distributed in 35-day phase provided details on the time and the energy dependence of the pulse shape and the spectra. It was found that a ...

We present a model for gamma-ray bursts (GRBs) in which a stellar mass black hole acquires a massive accretion disk by merging with the helium core of its red giant companion. The black hole enters the helium core after it, or its neutron star progenitor, first experiences a common envelope phase that carries it inward through the hydrogen envelope. ...

We present a model for gamma-ray bursts (GRB's) in which a stellar mass black hole acquires a massive accretion disk by merging with the helium core of its red giant companion. The black hole enters the helium core after first experiencing a common envelope phase that carries it inwards through the hydrogen envelope. Accretion of the ...

Models in which gamma-ray bursters are young neutron stars may be difficult to reconcile with the apparently isotropic distribution of observed bursts. To justify this statement, the distribution of old neutron stars in the Galaxy was calculated by integrating numerically some 90,000 orbits in the Galactic gravitational potential for up to 10 to the 10th yr. Other calculations ...

Using a worldwide combination of diverse telescopes, astronomers have discovered that a giant galaxy's bursts of very high energy gamma rays are coming from a region very close to the supermassive black hole at its core. The discovery provides important new information about the mysterious workings of the powerful "engines" in the centers of innumerable ...

The formation and evolution of an accretion disk formed during the collapse of a rotating cloud core

All the major viable acceleration mechanisms suggested so far in order to explain the energy of the gamma-rays observed from Cygnus X-3 are critically reviewed. It is argued that Cyg X-3 must be an accretion-fed strong X-ray binary with negligible orbital eccentricity and cannot contain a young active pulsar. It is shown that, for reasonable assumptions, the ...

A scenario for the central engine of AGN has been developed, consisting of a massive black hole (MBH) onto which gas accretes through an accretion disk. The accretion disk radiates the observed optical and ultraviolet continua. Surrounding the MBH is a no...

... X-ray spectra emitted by a hot plasma containing cold clouds - Malzac; Thermal Comptonization and Disk Reprocessing in the Type 1 Seyfert Galaxy NGC ...

duces some analytical solutions, such as a standing shock and a Keplerian disk with a steady state infall- ing corona or with a corona in hydrostatic equilibrium. ...

290 Stepinski:On Maonetic Dynamos in Thin Accretion Disks Around Stars pressure is smaller than gas pressure, otherwise the assumption of a thin disk ...

They could see details as fine as the neutron star's accretion disk, a ring of gas swirling around and flowing onto the neutron star, as the disk buckled ...

accretion disk where the viscosity is dominated by radiation pressure. ... viscosity norm. 2. 2cos /i d where i is the inclination of the disk and d is the ...

Derivations are made for the mass and the mass-turnover time scale of an accretion disk as a function of the accretion rate, the observed disk radius, the non-viscous disk radius, and two parameters. These parameters depend on the effectiveness of viscosity and tidal angular momentum loss. ...

Derivations are made for the mass and the mass-turnover time scale of an accretion disk as a function of the accretion rate, the observed disk radius, the non-viscous disk radius, and two parameters. These parameters depend on the effectiveness of viscosi...

Too hot accretion disks in ULX and superluminal jet sources ... Standard accretion disk around Kerr black hole can explain the hard disk spectra? ...

Accretion disks are invoked to explain a host of astrophysical phenomena, from protostellar objects to AGN. And yet the mechanism allowing accretion disks to operate are completely unknown. This proposal seeks to observe the ``smoking gun'' signature of magnetically-driven viscosity in ...

Soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are young and radio-quiet X-ray pulsars that have been rapidly spun-down to slow spin periods clustered in the range 5-12 s. Most of these unusual pulsars also appear to be associated with supernova shell remnants (SNRs) with typical ages less than 30 kyr. By examining the sizes of these remnants versus their ...

The Rossi X-ray Timing Explorer has observed a wide range of sources and is producing valuable science. Its broad-band sensitivity has been key in the observations of both compact, stellar, and nebular objects. RXTE is ideally suited for observing X-rays from both galactic and extragalactic black holes. The range of accretion rates, masses, and possibly angular momenta of ...

A collapsar is a massive rotating star (M ms ? 25 Msun) whose core collapses to form a black hole. In a rapidly rotating star, the accretion of the rest of the star into the newly-formed black hole produces an energetic long-duration gamma-ray burst (GRB) accompanied by a Type Ib/c supernova. An accretion disk ...