Modulation of the disk Emission by the AEI | AEI is a Model for the LFQPO

 

 

Microquasars - LFQPO / Modulation of the disk Emission by the AEI

A 2D verification of the non-linear evolution of the AEI was done by Caunt & Tagger (2001). The code, although based on a Zeus-type grid, is similar to that used for galactic spirals. It uses cylindrical coordinates with a radial logarimthic grid This allows high precision in the inner part of disk where he instability is developing, and a large dynamic range in r (typically 50 inner radii). The grid also avoids the need to impose a reflective outer boundary.

The code also implements the FARGO scheme (Masset, 2000) which enhances execution speed by eliminating the Keplerian speed from the Courant condition. As a last characteristic the disk is assumed to be in the vacuum which allows us to compute the magnetic field through a Poisson equation similar to the self-gravity case in galaxies.

 

 

 

 

We have upgraded the code by adding an energy equation and computing the local disk thickness using hydrostatic equilibrium. This provides the 3D view of the disk seen on the left. Working with M.Muno at MIT we computed the flux received from such a source and obtained a modulation with significant features comparable to that seen in the observed LFQPOs.

However the rms amplitude of the simulated light curve is only 5% while the observed one sometimes reaches 20%.

 

 

 

 

The source of the rms modulation in the AEI model results from a combination of two effects :
1) the anisotropy associated with the disk due to the presence of spiral waves
2) the disk inclination angle, and
3) the height of the hot spiral.

 

This difference in rms amplitude between the 2-D AEI and the observations very likely comes from the fact that the height of the spiral wave is not simulated but computed a posteriori.

 

To improve this situation requires 3-D simulations, which in turn will allow much more realistic synthetic spectra of microquasars to be produced. The 2-D simulations have at least demonstrated the possibility of obtaining such modulations.