Browsing FAS Scholarly Articles by Keyword "accretion"
Now showing items 1-15 of 15
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The constant inner-disk radius of LMC X-3: A basis for measuring black hole spin
(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. ... -
The flare activity of Sagittarius A*
(EDP Sciences, 2006)Context. We report new simultaneous near-infrared/sub-millimeter/X-ray observations of the SgrA* counterpart associated with the massive 3–4×106M⊙ black hole at the Galactic Center. Aims. The main aim is to investigate the ... -
General relativistic magnetohydrodynamic simulations of Blandford-Znajek jets and the membrane paradigm
(Oxford University Press (OUP), 2013)Recently it has been observed that the scaling of jet power with black hole spin in galactic X-ray binaries is consistent with the predictions of the Blandford-Znajek (BZ) jet model. These observations motivate us to revisit ... -
Location of the bow shock ahead of cloud G2 at the Galactic Centre
(Oxford University Press (OUP), 2013)We perform detailed magnetohydrodynamic simulations of the gas cloud G2 interacting with the accretion flow around the Galactic Center black hole Sgr A∗ . We take as our initial conditions a steady-state, converged solution ... -
Measuring the Spins of Stellar Black Holes: A Progress Report
(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. ... -
Photon-conserving Comptonization in simulations of accretion discs around black holes
(Oxford University Press (OUP), 2015)We introduce a new method for treating Comptonization in computational fluid dynamics. By construction, this method conserves the number of photons. Whereas the traditional “blackbody Comptonization” approach assumes that ... -
Ps1-10jh Continues to Follow the Fallback Accretion Rate of a Tidally Disrupted Star
(IOP Publishing, 2015)We present late-time observations of the tidal disruption event candidate PS1-10jh. UV and optical imaging with HST/WFC3 localize the transient to be coincident with the host galaxy nucleus to an accuracy of 0.023 arcsec, ... -
Radio and Millimeter Monitoring of Sgr A*: Spectrum, Variability, and Constraints on the G2 Encounter
(IOP Publishing, 2015)We report new observations with the Very Large Array, Atacama Large Millimeter Array, and Submillimeter Array at frequencies from 1.0 to 355 GHz of the Galactic Center black hole, Sagittarius A*. These observations were ... -
Radio light curves during the passage of cloud G2 near Sgr A*
(Oxford University Press (OUP), 2013)We calculate radio light curves produced by the bow shock that is likely to form in front of the G2 cloud when it penetrates the accretion disk of Sgr A∗ . The shock acceleration of the radioemitting electrons is captured ... -
Recoiling black holes: prospects for detection and implications of spin alignment
(Oxford University Press (OUP), 2015)Supermassive black hole (BH) mergers produce powerful gravitational wave emission. Asymmetry in this emission imparts a recoil kick to the merged BH, which can eject the BH from its host galaxy altogether. Recoiling BHs ... -
Semi-implicit scheme for treating radiation under M1 closure in general relativistic conservative fluid dynamics codes
(Oxford University Press (OUP), 2013)A numerical scheme is described for including radiation in multidimensional general relativistic conservative fluid dynamics codes. In this method, a covariant form of the M1 closure scheme is used to close the radiation ... -
The slimming effect of advection on black-hole accretion flows
(EDP Sciences, 2016)We study energy flows in geometrically thick accretion discs, both optically thick and thin, using general relativistic, three-dimensional simulations of black hole accretion flows. We find that for non-rotating black holes ... -
The spin of the black hole microquasar XTE J1550−564 via the continuum-fitting and Fe-line methods
(Oxford University Press (OUP), 2011)We measure the spin of XTE J1550-564 in two ways: by modelling the thermal continuum spectrum of the accretion disc, and independently by modeling the broad red wing of the reflection fluorescence Fe-K line. We find that ... -
Three-dimensional general relativistic radiation magnetohydrodynamical simulation of super-Eddington accretion, using a new code HARMRAD with M1 closure
(Oxford University Press (OUP), 2014)Black hole (BH) accretion flows and jets are dynamic hot relativistic magnetized plasma flows whose radiative opacity can significantly affect flow structure and behavior. We describe a numerical scheme, tests, and an ... -
Toward a New Geometric Distance to the Active Galaxy NGC 4258. II. Centripetal Accelerations and Investigation of Spiral Structure
(American Astronomical Society, 2008)We report measurements of centripetal accelerations of maser spectral components of NGC 4258 for 51 epochs spanning 1994 to 2004. This is the second paper of a series, in which the goal is the determination of a new geometric ...