Accretion-Ejection Instability in magnetized disks,
and low-frequency QPOs in GRS 1915+105
I will show that an Accretion-Ejection Instability may exist in the
inner regions of magnetized accretion disks. It appears as a large
scale, coherent spiral structure in the disk, whose properties make it a
very good candidate to explain the low frequency QPOs ( ~ 1 Hz)
observed in X ray binaries. The instability proceeds by extracting
angular momentum from the inner region of the disk; this momentum will
end up emitted as Alfven waves toward the corona of the disk, where it
might energize a jet or wind. The instability appears when the magnetic
pressure becomes comparable with the thermal pressure of the disk.
I will then discuss how this instability compares with the observations
of a low-frequency QPO in the low state of the micro-quasar GRS 1915+105.
This leads to a consistent scenario for the ~ 30 mn cycles of this
source, associated with relativistic ejections. In this ``Magnetic
Flood'' scenario, the cycles are controlled by the accumulation of
magnetic flux in the disk.
File translated from TEX by TTH, version 2.32.
On 16 Jul 1999, 09:19.