Estimating masses of Keplerian disk systems: the case of AGN in NGC 4258

The Keplerian motion of accretion disks in Active Galactic Nuclei (AGN) is usually believed to be generated by a heavy central mass. We investigate accreting disk systems with polytropic gas in Keplerian rotation and obtain a phenomenological formula that relates the Keplerian angular frequency to the ratio of disk and central masses. Central mass approaches the Keplerian value, if the inner boundary of a disk is close to the minimal stable orbit of a black hole. These results are applied to NGC 4258, the unique AGN with a finely measured Keplerian rotation curve of the central disk, with the conclusion that its rotation curve is, in fact, determined by the central black hole. The mass of the accretion disk exceeds 100 solar masses.Comment: 7 pages, 2 figures, to appear in Acta Phys. Pol.

General-relativistic rotation: self-gravitating fluid tori in motion around black holes

We obtain from the first principles a general-relativistic Keplerian rotation law for self-gravitating disks around spinning black holes. This is an extension of a former rotation law that was designed mainly for toroids around spin-less black holes. We integrate numerically axial stationary Einstein equations with self-gravitating disks around spinless or spinning black holes; that includes the first ever integration of the Keplerian selfgravitating tori. This construction can be used for the description of tight black hole-torus systems produced during coalescences of two neutron stars or modelling of compact active galactic nuclei.Comment: Matches published versio

Self-gravitating magnetised tori around black holes in general relativity

We investigate stationary, self-gravitating, magnetised disks (or tori) around black holes. The models are obtained by numerically solving the coupled system of the Einstein equations and the equations of ideal general-relativistic magnetohydrodynamics. The mathematical formulation and numerical aspects of our approach are similar to those reported in previous works modeling stationary self-gravitating perfect-fluid tori, but the inclusion of magnetic fields represents a new ingredient. Following previous studies of purely hydrodynamical configurations, we construct our models assuming Keplerian rotation in the disks and both spinning and spinless black holes. We focus on the case of a toroidal distribution of the magnetic field and build a large set of models corresponding to a wide range of values of the magnetisation parameter, starting with weakly magnetised disks and ending at configurations in which the magnetic pressure dominates over the thermal one. In all our models, the magnetic field affects the equilibrium structure of the torus mainly due to the magnetic pressure. In particular, an increasing contribution of the magnetic field shifts the location of the maximum of the rest-mass density towards inner regions of the disk. The total mass of the system and the angular momentum are affected by the magnetic field in a complex way, that depends on the black hole spin and the location of the inner radius of the disk. The non-linear dynamical stability of the solutions presented in this paper will be reported elsewhere.Comment: 17 pages, 5 figures, 1 tabl

Analytical and Numerical Analysis of Circumbinary Disk Dynamics -- I: Coplanar Systems

We present an analytical and numerical study of a system composed of a stellar binary pair and a massless, locally isothermal viscous accretion disk that is coplanar to the binary orbital plane. Analytically, we study the effect of the binary's gravitational potential over short timescales through the study of stability for epicyclic orbits, and over long timescales by revisiting the concept of resonant torques. Numerically, we perform two-dimensional Newtonian numerical simulations of the disk-binary system over a range of binary mass ratios. We find that the results of our simulations are consistent with previous numerical studies. We additionally show, by comparison of the analytical and numerical results, that the circumbinary gap is maintained on the orbital timescale through the driving of epicyclic instabilities, and does not depend on resonant torquing, contrary to standard lore. While our results are applicable to any disk-binary system, we highlight the importance of this result in the search for electromagnetic and gravitational-wave signatures from supermassive black-hole binaries

General-relativistic versus Newtonian: geometric dragging and dynamic anti-dragging in stationary disks in the first post-Newtonian approximation

We evaluate general-relativistic effects in motion of stationary accretion disks around a Schwarzschild black hole, assuming the first post-Newtonian (1PN) approximation. There arises an integrability condition, that leads to the emergence of two types of general-relativistic corrections to a Newtonian rotation curve. The well known geometric dragging of frames accelerates rotation but the hitherto unknown dynamic term, that reflects the disk structure, deccelerates rotation. The net result can diminish the Newtonian angular velocity of rotation in a central disk zone but the geometric dragging of frames dominates in the disk boundary zone. Both effects are nonlinear in nature and they disappear in the limit of test fluids. Dust disks can be only geometrically dragged while uniformly rotating gaseous disk are untouched at the 1PN order. General-relativistic contributions can strongly affect rotation periods in Keplerian motion for compact systems.Comment: Minor changes in the introduction and the summary. Accepted by the Physical Review D. 12 pages, 5 figure

On the Mechanism of Action of SJ-172550 in Inhibiting the Interaction of MDM4 and p53

SJ-172550 (1) was previously discovered in a biochemical high throughput screen for inhibitors of the interaction of MDMX and p53 and characterized as a reversible inhibitor (J. Biol. Chem. 2010; 285∶10786). Further study of the biochemical mode of action of 1 has shown that it acts through a complicated mechanism in which the compound forms a covalent but reversible complex with MDMX and locks MDMX into a conformation that is unable to bind p53. The relative stability of this complex is influenced by many factors including the reducing potential of the media, the presence of aggregates, and other factors that influence the conformational stability of the protein. This complex mechanism of action hinders the further development of compound 1 as a selective MDMX inhibitor

Structures of relevant compounds.

<p><b>Panel A.</b> Structure of SJ-172550 (<b>1</b>) and a non-reactive analog (<b>2</b>). <b>Panel B.</b> The potential mechanism of covalent adduct formation.</p

Inhibition of MDMX-p53 peptide binding by compound 1 (IC₅₀ = 3 µM), compound 2 (IC₅₀>100 uM).

<p>Inhibition of MDMX-p53 peptide binding by compound 1 (IC₅₀ = 3 µM), compound 2 (IC₅₀>100 uM).</p

Thermal stability equilibria of MDMX.

<p><b>Panel a.</b> Thermal shift data for MDMX (23–111) showing a 7 degree stabilization of the protein’s melting point by addition of compound <b>1</b>. The panel shows individual data sampling points from 3 independent experiments from each condition. <b>Panel b.</b> Dose dependency and time dependency of the effect showing an apparent EC₅₀ of roughly 1 µM and minimal time dependency. <b>Panel c.</b> Dose dependent reversal of the effects of compound <b>1</b> by TCEP. <b>Panel d.</b> Dose dependent reversal of the effects of compound <b>1</b> by DTT.</p