Mean azimuthal magnetic field in r-z plane
Movie of azimuthally averaged toroidal field (1.3 Mb, mpeg)
The animations are derived from global magnetohydrodynamic simulations of disk
accretion in a pseudo-Newtonian potential (Paczynski and Wiita 1980). The main
goal of the simulations is to investigate the predicted variability of accreting
black holes. The models
are three-dimensional but vertically unstratified and isothermal, and are
computed in cylindrical co-ordinates using the ZEUS MHD code at a resolution
of 288 (phi) x 192 (r) x 48 (z) mesh points. We compute the "emission" in the
disk rest frame using several slightly different prescriptions, but in all
cases the basic assumption is that the local magnetic stress traces regions
of high dissipation.
To make the images and compute the lightcurve, we calculate the mapping between
the rest frame emission and that seen by a distant observer (the "transfer
function"), using a ray tracing method that models the relevant relativistic
effects. Because of the
high Doppler shift near the marginally stable orbit, there is a strong K-correction
which alters the detailed appearance of the images depending upon the assumed
spectrum of the source. We have assumed a power-law spectrum with an index of -1 in constructing
the movies shown above.
The movies show about half of the simulation data analyzed in the paper, and
do not take account of the differing time of flight of photons from different
regions of the accretion disk, though this effect is included in our calculations
of light curves and power spectra. Nor have we attempted
to visualize the redshift of different part of the disk - our
attempts to do this haven't looked very good.
The variability of accretion onto Schwarzschild black holes from turbulent magnetized disks,
Philip J. Armitage and Christopher S. Reynolds, MNRAS, 341, 1041 (2003).