Browsing by Author "Narayan, Ramesh"

Now showing items 1-20 of 99

    • Advection-dominated accretion and the black hole event horizon 

      Narayan, Ramesh; McClintock, Jeffrey E. (Elsevier BV, 2008)
      As the luminosity of an accreting black hole drops to a few percent of Eddington, the spectrum switches from the familiar soft state to a hard state that is well-described by a distended and tenuous advection-dominated ...

    • Angular Momentum Transport in Convectively Unstable Shear Flows 

      Käpylä, Petri J.; Brandenburg, Axel; Korpi, Maarit J.; Snellman, Jan E.; Narayan, Ramesh (IOP Publishing, 2010)
      Angular momentum transport due to hydrodynamic turbulent convection is studied using local three-dimensional numerical simulations employing the shearing box approximation. We determine the turbulent viscosity from nonrotating ...

    • Birth of a relativistic outflow in the unusual γ-ray transient Swift J164449.3+573451 

      Zauderer, Bevin Ashley; Berger, Edo; Soderberg, Alicia M.; Loeb, Abraham; Narayan, Ramesh; Frail, D. A.; Petitpas, Glen Raymond; Brunthaler, A.; Chornock, Ryan T.; Carpenter, J. M.; Pooley, G. G.; Mooley, K.; Kulkarni, S. R.; Margutti, Raffaella; Fox, D. B.; Nakar, E.; Patel, Nimesh A.; Volgenau, N. H.; Culverhouse, T. L.; Bietenholz, M. F.; Rupen, M. P.; Max-Moerbeck, W.; Readhead, A. C. S.; Richards, J.; Shepherd, M.; Storm, S.; Hull, Charles L. H. (Springer Nature, 2011)
      Active galactic nuclei, which are powered by long-term accretion onto central supermassive black holes, produce1 relativistic jets with lifetimes of at least one million years, and the observation of the birth of such a ...

    • Black Hole Accretion Disks and Jets: Connecting Simulations and Theory 

      Penna, Robert Francis (2013-09-25)
      In recent years, general relativistic magnetohydrodynamic (GRMHD) simulations have produced more realistic models for black hole disks and jets. However the complexity of the simulations has created a disconnect between ...

    • The Black Hole Mass Distribution in the Galaxy 

      Özel, Feryal; Psaltis, Dimitrios; Narayan, Ramesh; McClintock, Jeffrey E. (IOP Publishing, 2010)
      We use dynamical mass measurements of 16 black holes in transient low-mass X-ray binaries to infer the stellar black hole mass distribution in the parent population. We find that the observations are best described by a ...

    • Black Hole Spin and the Radio Loud/Quiet Dichotomy of Active Galactic Nuclei 

      Tchekhovskoy, Alexander; Narayan, Ramesh; McKinney, Jonathan C. (IOP Publishing, 2010)
      Radio loud active galactic nuclei (AGNs) are on average 1000 times brighter in the radio band compared to radio quiet AGNs. We investigate whether this radio loud/quiet dichotomy can be due to differences in the spin of ...

    • Black Hole Spin via Continuum Fitting and the Role of Spin in Powering Transient Jets 

      McClintock, Jeffrey E.; Narayan, Ramesh; Steiner, James (Springer Science + Business Media, 2013)
      The spins of ten stellar black holes have been measured using the continuum- fitting method. These black holes are located in two distinct classes of X-ray binary systems, one that is persistently X-ray bright and another ...

    • Bondi Flow from a Slowly Rotating Hot Atmosphere 

      Narayan, Ramesh; Fabian, Andrew C. (Oxford University Press (OUP), 2011)
      A supermassive black hole in the nucleus of an elliptical galaxy at the centre of a cool-core group or cluster of galaxies is immersed in hot gas. Bondi accretion should occur at a rate determined by the properties of the ...

    • The Bright Side of Black Holes: Radiation From Black Hole Accretion Disks 

      Zhu, Yucong (2015-05-15)
      An understanding of radiation is paramount for connecting observations of accretion disks with the theory of black holes. In this thesis, we explore via radiative transfer postprocessing calculations the observational ...

    • Confirmation via the Continuum-Fitting Method That the Spin of the Black Hole in Cygnus X-1 Is Extreme 

      Gou, Lijun; McClintock, Jeffrey E.; Remillard, Ronald A.; Steiner, James F.; Reid, Mark J.; Orosz, Jerome A.; Narayan, Ramesh; Hanke, Manfred; García, Javier (IOP Publishing, 2014)
      In Gou et al., we reported that the black hole primary in the X-ray binary Cygnus X-1 is a near-extreme Kerr black hole with a spin parameter a∗ > 0.95 (3σ). We confirm this result while setting a new and more stringent ...

    • The constant inner-disk radius of LMC X-3: A basis for measuring black hole spin 

      Steiner, James; McClintock, Jeffrey E.; Remillard, Ronald A.; Gou, Lijun; Yamada, Shin; Narayan, Ramesh (IOP Publishing, 2010)
      he black hole binary system LMC X-3 has been observed by virtually every X-ray mission since the inception of X-ray astronomy. Among the persistent sources, LMC X-3 is uniquely both habitually soft and highly variable. ...

    • Constraints on cold magnetized shocks in gamma-ray bursts 

      Narayan, Ramesh; Kumar, Pawan; Tchekhovskoy, Alexander (Oxford University Press (OUP), 2011)
      We consider a model in which the ultra-relativistic jet in a gamma-ray burst (GRB) is cold and magnetically accelerated. We assume that the energy flux in the outflowing material is partially thermalized via internal shocks ...

    • The Cool Accretion Disk in ESO 243-49 HLX-1: Further Evidence of an Intermediate-Mass Black Hole 

      Davis, Shane W.; Narayan, Ramesh; Zhu, Yucong; Barret, Didier; Farrell, Sean A.; Godet, Olivier; Servillat, Mathieu; Webb, Natalie A. (IOP Publishing, 2011)
      With an inferred bolometric luminosity exceeding \(10^{42}\;erg\;s^{–1}\), HLX-1 in ESO 243-49 is the most luminous of ultraluminous X-ray sources and provides one of the strongest cases for the existence of intermediate-mass ...

    • The Damping Rates of Embedded Oscillating Starless Cores 

      Broderick, Avery E.; Narayan, Ramesh; Keto, Eric; Lada, Charles J. (IOP Publishing, 2008)
      In a previous paper we demonstrated that nonradial hydrodynamic oscillations of a thermally supported (BonnorEbert) sphere embedded in a low-density, high-temperature medium persist for many periods. The predicted column ...

    • A Determination of the Spin of the Black Hole Primary in LMC X-1 

      Gou, Lijun; McClintock, Jeffrey E.; Liu, Jifeng; Narayan, Ramesh; Steiner, James; Remillard, Ronald A.; Orosz, Jerome A.; Davis, Shane W.; Ebisawa, Ken; Schlegel, Eric M. (IOP Publishing, 2009)
      The first extragalactic X-ray binary, LMC X-1, was discovered in 1969. In the 1980s, its compact primary was established as the fourth dynamical black hole candidate. Recently, we published accurate values for the mass of ...

    • Distinguishing black holes from naked singularities through their accretion disc properties 

      Joshi, Pankaj S; Malafarina, Daniele; Narayan, Ramesh (IOP Publishing, 2013)
      We show that, in principle, a slowly evolving gravitationally collapsing perfect fluid cloud can asymptotically settle to a static spherically symmetric equilibrium configuration with a naked singularity at the center. We ...

    • Double-peaked narrow-line signatures of dual supermassive black holes in galaxy merger simulations 

      Blecha, L.; Loeb, A.; Narayan, Ramesh (Oxford University Press (OUP), 2013)
      We present a first attempt to model the narrow-line (NL) region of active galactic nuclei (AGN) in hydrodynamic simulations of galaxy mergers, using a novel physical prescription. This model is used to determine the origin ...

    • Dynamical constraints on the Local Group from the CMB and 2MRS dipoles 

      Loeb, Abraham; Narayan, Ramesh (Oxford University Press (OUP), 2008)
      We place constraints on the dynamics of the Local Group (LG) by comparing the dipole of the Cosmic Microwave Background (CMB) with the peculiar velocity induced by the 2MRS galaxy sample. The analysis is limited by the ...

    • Efficiency of Magnetic to Kinetic Energy Conversion in a Monopole Magnetosphere 

      Tchekhovskoy, Alexander; McKinney, Jonathan C.; Narayan, Ramesh (IOP Publishing, 2009)
      Unconfined relativistic outflows from rotating, magnetized compact objects are often well modeled by assuming that the field geometry is approximately a split-monopole at large radii. Earlier work has indicated that such ...

    • Efficient generation of jets from magnetically arrested accretion on a rapidly spinning black hole 

      Tchekhovskoy, Alexander; Narayan, Ramesh; McKinney, Jonathan C. (Oxford University Press (OUP), 2011)
      We describe global, 3D, time‐dependent, non‐radiative, general‐relativistic, magnetohydrodynamic simulations of accreting black holes (BHs). The simulations are designed to transport a large amount of magnetic flux to the ...