Short-duration gamma-ray bursts from off-axis collapsars (2009)
Lazzati, Davide, Morsony, Brian J., Begelman, Mitchell C.
We present 2D high resolution hydrodynamic simulations of the relativistic outflows of long-duration gamma-ray burst progenitors. We analyze the properties of the outflows at wide off-axis angles,...
Evolution of supermassive stars as a pathway to black hole formation (2009)
Supermassive stars, with masses greater than a million solar masses, are possible progenitors of supermassive black holes in galactic nuclei. Because of their short nuclear burning timescales, such...
Fast TeV variability from misaligned minijets in the jet of M87 (2009)
Giannios, Dimitrios, Uzdensky, Dmitri A., Begelman, Mitchell C.
The jet of the radio galaxy M87 is misaligned, resulting in a Doppler factor delta~1 for emission of plasma moving parallel to the jet. This makes the observed fast TeV flares on timescales of...
Fast TeV variability in blazars: jet in a jet (2009)
Giannios, Dimitrios, Uzdensky, Dmitri A., Begelman, Mitchell C.
The fast TeV variability of the blazars Mrk 501 and PKS 2155--304 implies a compact emitting region that moves with a bulk Lorentz factor of Gamma_{em}~100 toward the observer. The Lorentz factor is...
Fast TeV variability in blazars: jets in a jet (2009)
Giannios, Dimitrios, Uzdensky, Dmitri A., Begelman, Mitchell C.
Delayed X-ray emission from fallback in compact-object mergers (2008)
Rossi, Elena M., Begelman, Mitchell C.
When double neutron star or neutron star-black hole binaries merge, the final remnant may comprise a central solar-mass black hole surrounded by a 0.01-0.1 solar masses torus. The subsequent...
X-ray flares, neutrino cooled disks, and the dynamics of late accretion in GRB engines (2008)
Lazzati, Davide, Perna, Rosalba, Begelman, Mitchell C.
We compute the average luminosity of X-ray flares as a function of time, for a sample of 10 long-duration gamma-ray burst afterglows. The mean luminosity, averaged over a timescale longer than the...
X-ray flares and their relation to the inner engine activity of GRBs (2008)
Lazzati, Davide, Morsony, Brian J., Perna, Rosalba, Begelman, Mitchell C.
Flares overlaid on the smooth power-law decay of Swift X-ray afterglows are rather common, appearing in roughly half the observed light curves. They are a manifestation of the late time activity of...
Hot self-similar relativistic MHD flows (2008)
Zakamska, Nadia L., Begelman, Mitchell C., Blandford, Roger D.
We consider axisymmetric relativistic jets with a toroidal magnetic field and an ultrarelativistic equation of state, with the goal of studying the lateral structure of jets whose pressure is matched...
Quasistars: Accreting black holes inside massive envelopes (2007)
Begelman, Mitchell C., Rossi, Elena M., Armitage, Philip J.
We study the structure and evolution of "quasistars", accreting black holes embedded within massive hydrostatic gaseous envelopes. These configurations may model the early growth of supermassive...
Christopher S. Reynolds, Mitchell C. Begelman
fluorescence from within the innermost stable
Implications of very rapid TeV variability in blazars (2007)
Begelman, Mitchell C., Fabian, Andrew C., Rees, Martin J.
We discuss the implications of rapid (few-minute) variability in the TeV flux of blazars, which has been observed recently with the HESS and MAGIC telescopes. The variability timescales seen in PKS...
Did supermassive black holes form by direct collapse? (2007)
Rapid infall of gas in the nuclei of galaxies could lead to the formation of black holes by direct collapse, without first forming stars. Black holes formed in this way would have initial masses of a...
The physics of GRB jets and their interaction with the progenitor star (2006)
Lazzati, Davide, Morsony, Brian J., Begelman, Mitchell C.
It is now generally accepted that long gamma-ray bursts are associated with the final evolutionary stages of massive stars. As a consequence, their jets must propagate through the stellar progenitor...
Gamma-Ray Burst jet dynamics and their interaction with the progenitor star (2006)
Lazzati, Davide, Morsony, Brian J., Begelman, Mitchell C.
The association of at least some long gamma-ray bursts with type Ic supernova explosions has been established beyond reasonable doubt. Theoretically, the challenge is to explain the presence of a...
Temporal and Angular Properties of GRB Jets Emerging from Massive Stars (2006)
Morsony, Brian J., Lazzati, Davide, Begelman, Mitchell C.
We study the long-term evolution of relativistic jets in collapsars and examine the effects of viewing angle on the subsequent gamma ray bursts. We carry out a series of high-resolution simulations...
Trapping of magnetic flux by the plunge region of a black hole accretion disk (2006)
Reynolds, Christopher S., Garofalo, David, Begelman, Mitchell C.
The existence of the radius of marginal stability means that accretion flows around black holes invariably undergo a transition from a MHD turbulent disk-like flow to an inward plunging flow. We...
Formation of Supermassive Black Holes by Direct Collapse in Pregalactic Halos (2006)
Begelman, Mitchell C., Volonteri, Marta, Rees, Martin J.
We describe a mechanism by which supermassive black holes can form directly in the nuclei of protogalaxies, without the need for seed black holes left over from early star formation. Self-gravitating...
Photon Bubbles and the Vertical Structure of Accretion Disks (2006)
We consider the effects of "photon bubble" shock trains on the vertical structure of radiation pressure-dominated accretion disks. These density inhomogeneities are expected to develop spontaneously...
Thick fireballs and the steep decay in the early X-ray afterglow of gamma-ray bursts (2005)
Lazzati, Davide, Begelman, Mitchell C.
We study the early afterglows of gamma-ray bursts produced by geometrically thick fireballs, following the development of the external shock as energy is continually supplied to the shocked material....
Are Quasar Jets Matter or Poynting Flux Dominated? (2005)
Sikora, Marek, Madejski, Greg M., Lasota, Jean-Pierre, Begelman, Mitchell C.
If quasar jets are accelerated by magnetic fields but terminate as matter dominated, where and how does the transition occur between the Poynting-dominated and matter-dominated regimes? To address...
Nonlinear Photon Bubbles Driven by Buoyancy (2005)
We derive an analytic model for nonlinear "photon bubble" wave trains driven by buoyancy forces in magnetized, radiation pressure-dominated atmospheres. Continuous, periodic wave solutions exist when...
Begelman, Mitchell C., Nath, Biman B.
We argue that the velocity dispersions and masses of galactic bulges and spheroids are byproducts of the feedback that regulates rapid black hole growth in protogalaxies. We suggest that the feedback...
Cyclotron Maser Emission from Blazar Jets? (2005)
Begelman, Mitchell C., Ergun, Robert E., Rees, Martin J.
We consider the production of electron cyclotron maser emission by low-density, highly magnetized plasmas in relativistic jets. The population inversion required to drive cyclotron maser instability...
Are quasar jets dominated by Poynting flux? (2005)
Sikora, Marek, Begelman, Mitchell C., Madejski, Greg M., Lasota, Jean-Pierre
The formation of relativistic astrophysical jets is presumably mediated by magnetic fields threading accretion disks and central, rapidly rotating objects. As it is accelerated by magnetic stresses,...
Entropy "floor" and effervescent heating of intracluster gas (2004)
Roychowhury, Suparna, Ruszkowski, M., Nath, Biman B., Begelman, Mitchell C.
Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations)
Constraining the Structure of GRB Jets Through the log(N)-log(S) Distribution (2004)
Guetta, Dafne, Granot, Jonathan, Begelman, Mitchell C.
A general formalism is developed for calculating the luminosity function and the expected number $N$ of observed GRBs above a peak photon flux $S$ for any GRB jet structure. This new formalism...
Disk Outflows and the Accretion Rate Gap (2004)
Begelman, Mitchell C., Celotti, Annalisa
We argue that the observed `accretion rate gap' - between black holes in radio-loud active galactic nuclei (AGN) accreting at close to the Eddington limit and those accreting at considerably lower...
3D simulations of viscous dissipation in the intracluster medium (2004)
Ruszkowski, Mateusz, Bruggen, Marcus, Begelman, Mitchell C.
We present three-dimensional simulations of viscous dissipation of AGN induced gas motions and waves in clusters of galaxies. These simulations are motivated by recent detections of ripples in the...
Mechanical heating by active galaxies (2004)
Begelman, Mitchell C., Ruszkowski, Mateusz
Jets and winds are significant channels for energy loss from accreting black holes. These outflows mechanically heat their surroundings, through shocks as well as gentler forms of heating. We discuss...
Entropy "floor" and effervescent heating of intracluster gas (2004)
Roychowdhury, S., Ruszkowski, M., Nath, B. B., Begelman, Mitchell C.
Recent X-ray observations of clusters of galaxies have shown that the entropy of the intracluster medium (ICM), even at radii as large as half the virial radius, is higher than that expected from...
Cluster Heating by Viscous Dissipation of Sound Waves (2003)
Ruszkowski, Mateusz, Bruggen, Marcus, Begelman, Mitchell C.
We simulate the effects of viscous dissipation of waves that are generated by AGN activity in clusters of galaxies. We demonstrate that the amount of viscous heating associated with the dissipation...
Two Dimensional Adiabatic Flows onto a Black Hole: I. Fluid Accretion (2003)
Blandford, Roger D., Begelman, Mitchell C.
When gas accretes onto a black hole, at a rate either much less than or much greater than the Eddington rate, it is likely to do so in an "adiabatic" or radiatively inefficient manner. Under fluid...
AGN Feedback Mechanisms (2003)
Accreting black holes can release enormous amounts of energy to their surroundings, in various forms. Such feedback may profoundly influence a black hole's environment. After briefly reviewing the...
Impact of AGNs on the Surrounding Medium (2002)
The time- and ensemble-averaged mechanical energy outputs of radio galaxies may be large enough to offset much of the cooling inferred from X-ray observations of galaxy clusters. But does this...
Heating, conduction and minimum temperatures in cooling flows (2002)
Ruszkowski, Mateusz, Begelman, Mitchell C.
There is mounting observational evidence from Chandra for strong interaction between keV gas and AGN in cooling flows. It is now widely accepted that the temperatures of cluster cores are maintained...
Eddington limit and radiative transfer in highly inhomogeneous atmospheres (2002)
Ruszkowski, Mateusz, Begelman, Mitchell C.
Radiation dominated accretion disks are likely to be subject to the ``photon bubble'' instability, which may lead to strong density inhomogeneities on scales much shorter than the disk scale height....
Super-Eddington Fluxes from Thin Accretion Disks? (2002)
Radiation pressure-dominated accretion disks are predicted to exhibit strong density inhomogeneities on scales much smaller than the disk scale height, due to the nonlinear development of photon...
Heinz, Sebastian, Choi, Yun-Young, Reynolds, Christopher S., Begelman, Mitchell C.
We present Chandra observations of the galaxy cluster A4059. We find strong evidence that the FR-I radio galaxy PKS 2354-35 at the center of A4059 is inflating cavities with radii ~20 kpc in the...
Circular polarization from stochastic synchrotron sources (2001)
Ruszkowski, Mateusz, Begelman, Mitchell C.
The transfer of polarized radiation in stochastic synchrotron sources is explored by means of analytic treatment and Monte Carlo simulations. We argue that the main mechanism responsible for the...
Wilms, Joern, Reynolds, Christopher S., Begelman, Mitchell C., Reeves, James, Molendi, Silvano, Stuabert, Ruediger, ...
We present XMM-Newton European Photon Imaging Camera (EPIC) observations of the bright Seyfert 1 galaxy MCG-6-30-15, focusing on the broad Fe K$\alpha$ line at ~6keV and the associated reflection...
Super-Eddington Atmospheres that Don't Blow Away (2000)
We show that magnetized, radiation dominated atmospheres can support steady state patterns of density inhomogeneity that enable them to radiate at far above the Eddington limit, without suffering...
The Evolutionary Status of SS433 (1999)
King, Andrew R., Taam, Ronald E., Begelman, Mitchell C.
We consider possible evolutionary models for SS 433. We assume that common-envelope evolution is avoided if radiation pressure is able to expel most of a super-Eddington accretion flow from a region...
Hydrodynamical Non-radiative Accretion Flows in Two-Dimensions (1999)
Stone, James M., Pringle, James E., Begelman, Mitchell C.
Two-dimensional (axially symmetric) numerical hydrodynamical calculations of accretion flows which cannot cool through emission of radiation are presented. The calculations begin from an equilibrium...
Radiatively-Driven Outflows and Avoidance of Common-Envelope Evolution in Close Binaries (1999)
King, Andrew R., Begelman, Mitchell C.
Recent work on Cygnus X-2 suggests that neutron-star or black-hole binaries survive highly super-Eddington mass transfer rates without undergoing common-envelope evolution. We suggest here that the...
RXTE Observation of Cygnus X--1: III. Implications for Compton Corona and ADAF Models (1998)
Nowak, Michael A., Wilms, Joern, Vaughan, Brian A., Dove, James B., Begelman, Mitchell C.
We have recently shown that a `sphere+disk' geometry Compton corona model provides a good description of Rossi X-ray Timing Explorer (RXTE) observations of the hard/low state of Cygnus X--1....
HST Observations of the Broad Absorption Line Quasar PG 0946+301 (1998)
Arav, Nahum, Korista, Kirk T., De Kool, Martijn, Junkkarinen, Vesa T., Begelman, Mitchell C.
We analyze HST and ground based spectra of the brightest BALQSO in the UV: PG~0946+301. A detailed study of the absorption troughs as a function of velocity is presented, facilitated by the use of a...
A Model for the Moving `Wisps' in the Crab Nebula (1998)
I propose that the moving `wisps' near the center of the Crab Nebula result from nonlinear Kelvin-Helmholtz instabilities in the equatorial plane of the shocked pulsar wind. Recent observations...
RXTE Observation of Cygnus X-1: II. Timing Analysis (1998)
Nowak, Michael A., Vaughan, Brian A., Wilms, Joern, Dove, James B., Begelman, Mitchell C.
We present timing analysis for a Rossi X-ray Timing Explorer observation of Cygnus X-1 in its hard/low state. This was the first RXTE observation of Cyg X-1 taken after it transited back to this...
Radiation-Driven Warping. II. Non-Isothermal Disks (1998)
Maloney, Philip R., Begelman, Mitchell C., Nowak, Michael A.
Recent work by Pringle and by Maloney, Begelman & Pringle has shown that geometrically thin, optically thick, accretion disks are unstable to warping driven by radiation torque from the central...
X-ray Signatures of Evolving Radio Galaxies (1998)
Heinz, Sebastian, Reynolds, Christopher S., Begelman, Mitchell C.
We present a simple model for an evolving radio galaxy, as it expands into the hot, X-ray emitting interstellar medium (ISM) of its host galaxy or similarly into the hot intracluster medium (ICM) of...
RXTE Observation of Cygnus X-1: II. Timing Analysis (1998)
Michael A. Nowak, Brian A. Vaughan, Jörg Wilms, James B. Dove, Mitchell C. Begelman
We present timing analysis for a Rossi X-ray Timing Explorer observation of Cygnus X-1 in its hard/low state. This was the first RXTE observation of Cyg X-1 taken after it transited back to this...
Young radio galaxies and their environments (1997)
Many of the powerful radio galaxies observed at high redshift are very small, presumably because they are very young. A simple model, which treats the radio source as a bubble expanding into a...
The Origin of Warped, Precessing Disks in X-Ray Binaries (1997)
Maloney, Philip R., Begelman, Mitchell C.
The radiation-driven warping instability discovered by Pringle holds considerable promise as the mechanism responsible for producing warped, precessing accretion disks in X-ray binaries. This...
Instability of toroidal magnetic field in jets and plerions (1997)
Jets and pulsar-fed supernova remnants (plerions) tend to develop highly organized toroidal magnetic field. Such a field structure could explain the polarization properties of some jets, and...
RXTE Observation of Cygnus X-1: Spectral Analysis (1997)
Dove, James B., Wilms, Jorn, Nowak, Michael A., Vaughan, Brian A., Begelman, Mitchell C.
We present the results of the analysis of the broad-band spectrum of Cygnus X-1 from 3.0 to 200 keV, using data from a 10 ksec observation by the Rossi X-ray Timing Explorer. The spectrum can be well...
Iron fluorescence from within the innermost stable orbit of black hole accretion disks (1997)
Reynolds, Christopher S., Begelman, Mitchell C.
The fluorescent iron Ka line is a powerful observational probe of the inner regions of black holes accretion disks. Previous studies have assumed that only material outside the radius of marginal...
Dove, James B., Wilms, Jorn, Maisack, Michael, Begelman, Mitchell C.
We apply our self-consistent accretion disk corona (ADC) model, with two different geometries, to the broad-band X-ray spectrum of the black hole candidate Cygnus X-1. As shown in a companion paper...
Dove, James B., Wilms, Jorn, Begelman, Mitchell C.
We present the properties of accretion disk corona (ADC) models, where the radiation field, the temperature, and the total opacity of the corona are determined self-consistently. We use a non-linear...
Radiation-Driven Warping: The Origin of Warps and Precession in Accretion Disks (1996)
Maloney, Philip R., Begelman, Mitchell C., Pringle, J. E.
A geometrically thin, optically thick, warped accretion disk with a central source of luminosity is subject to non-axisymmetric forces due to radiation pressure; the resulting torque acts to modify...
Maloney, Philip R., Begelman, Mitchell C.
A geometrically thin, optically thick, warped accretion disk with a central source of luminosity is subject to non-axisymmetric forces due to radiation pressure; the resulting torque acts to modify...
The Compton Mirror in NGC 4151 (1996)
Poutanen, Juri, Sikora, Marek, Begelman, Mitchell C., Magdziarz, Pawel
We show that the sharp cutoff in the hard X-ray spectrum of NGC 4151, unusual for Seyfert 1 galaxies, can be reconciled with the average Seyfert 1 spectrum if we assume that the central source is...
ON THE GEOMETRY OF THE X-RAY EMITTING REGION IN SEYFERT GALAXIES (1995)
Stern, Boris E., Poutanen, Juri, Svensson, Roland, Sikora, Marek, Begelman, Mitchell C.
For the first time, detailed radiative transfer calculations of Comptonized X-ray and gamma-ray radiation in a hot pair plasma above a cold accretion disk are performed using two independent codes...
Gamma-Ray Bursts from Blast Waves Around Galactic Nuetron Stars (1993)
Begelman, Mitchell C., Meszaros, P., Rees, Martin J.
If gamma-ray bursts originate in our Galaxy, they probably involve violent disturbances in the magnetospheres of neutron stars. Any event of this kind is likely to trigger the sudden expulsion of...