Browsing by Author "Penna, Robert"

Now showing items 1-7 of 7

    • 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 eye of the storm: light from the inner plunging region of black hole accretion discs 

      Zhu, Yucong; Davis, Shane W.; Narayan, Ramesh; Kulkarni, Akshay K.; Penna, Robert Francis; McClintock, Jeffrey E. (Oxford University Press (OUP), 2012)
      It is generally thought that the light coming from the inner plunging region of black hole accretion discs contributes negligibly to the disc's overall spectrum, i.e. the plunging fluid is swallowed by the black hole before ...

    • GRMHD simulations of magnetized advection-dominated accretion on a non-spinning black hole: role of outflows 

      Narayan, Ramesh; Sadowski, Aleksander; Penna, Robert Francis; Kulkarni, Akshay K. (Oxford University Press (OUP), 2012)
      We present results from two long-duration GRMHD simulations of advection-dominated accretion around a non-spinning black hole. The first simulation was designed to avoid significant accumulation of magnetic flux around the ...

    • Measuring Black Hole Spin by the Continuum-Fitting Method: Effect of Deviations from the Novikov-Thorne Disc Model 

      Kulkarni, Akshay K.; Penna, Robert Francis; Shcherbakov, Roman V.; Steiner, James Francis; Narayan, Ramesh; Sadowski, Aleksander; Zhu, Yucong; McClintock, Jeffrey E.; Davis, Shane W.; McKinney, Jonathan C. (Oxford University Press (OUP), 2011)
      The X-ray spectra of accretion discs of eight stellar mass black holes have been analysed to date using the thermal continuum-fitting method, and the spectral fits have been used to estimate the spin parameters of the black ...

    • Measuring the spins of accreting black holes 

      McClintock, Jeffrey E.; Narayan, Ramesh; Davis, Shane W.; Gou, Lijun; Kulkarni, Akshay; Orosz, Jerome A; Penna, Robert Francis; Remillard, Ronald A; Steiner, James Francis (IOP Publishing, 2011)
      A typical galaxy is thought to contain tens of millions of stellar-mass black holes, the collapsed remnants of once massive stars, and a single nuclear supermassive black hole. Both classes of black holes accrete gas from ...

    • Measuring the Spins of Stellar Black Holes: A Progress Report 

      McClintock, Jeffrey E.; Narayan, Ramesh; Gou, L.; Liu, J.; Penna, R; Steiner, J; Comastri, A.; Angelini, L.; Cappi, Marina Christine (American Institute of Physics, 2010)
      We use the Novikov-Thorne thin disk model to fit the thermal continuum X-ray spectra of black hole X-ray binaries, and thereby extract the dimensionless spin parameter a∗=a/M of the black hole as a parameter of the fit. ...

    • Simulations of magnetized discs around black holes: Effects of black hole spin, disc thickness and magnetic field geometry 

      Penna, Robert; McKinney, Jonathan C.; Narayan, Ramesh; Tchekhovskoy, Alexander; Shafee, Rebecca; McClintock, Jeffrey E. (Oxford University Press (OUP), 2010)
      The standard general relativistic model of a razor-thin accretion disc around a black hole, developed by Novikov & Thorne (NT) in 1973, assumes the shear stress vanishes at theradius of the innermost stable circular orbit ...