504 citations · 1.9k across the 22 of their papers we have counts for
22 papers
A new equilibrium torus solution and GRMHD initial conditions
Robert F. Penna, Akshay Kulkarni, Ramesh Narayan
General relativistic magnetohydrodynamic (GRMHD) simulations are providing influential models for black hole spin measurements, gamma ray bursts, and supermassive black hole feedba…
Analytical Hot Spot Shapes and Magnetospheric Radius from 3D Simulations of Magnetospheric Accretion
Akshay K. Kulkarni, Marina M. Romanova
We present an analytical formula for the position and shape of the spots on the surface of accreting magnetized stars in cases where a star has a dipole magnetic field tilted at a…
The Shakura-Sunyaev Viscosity Prescription with Variable alpha(r)
Robert F. Penna, Aleksander Sadowski, Akshay K. Kulkarni +1
Almost all hydrodynamic accretion disk models parametrize viscosity with the dimensionless parameter alpha. There is no detailed model for alpha, so it is usually taken to be a con…
GRMHD Simulations of Magnetized Advection Dominated Accretion on a Non-Spinning Black Hole: Role of Outflows
Ramesh Narayan, Aleksander Sadowski, Robert F. Penna +1
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 significan…
The Eye of the Storm: Light from the Inner Plunging Region of Black Hole Accretion Discs
Yucong Zhu, Shane W. Davis, Ramesh Narayan +3
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…
Measuring Black Hole Spin by the Continuum-Fitting Method: Effect of Deviations from the Novikov-Thorne Disc Model
Akshay K. Kulkarni, Robert F. Penna, Roman V. Shcherbakov +7
The X-ray spectra of accretion discs of eight stellar-mass black holes have been analyzed to date using the thermal continuum fitting method, and the spectral fits have been used t…