The detectability of gravitational wave (GW) radiation from accretion disks
is discussed based on various astrophysical contexts. In order to emit GW
radiation, the disk shape should lose axial symmetry. We point out that a
significant deformation is plausible in non-radiative hot accretion disks
because of enhanced magnetic activity, whereas it is unlikely for standard-type
cool disks. We have analyzed the 3D magnetohydrodynamical (MHD) simulation data
of magnetized accretion flow, finding non-axisymmetric density patterns. The
corresponding ellipticity is ϵ∼0.01. The expected time variations
of GW radiation are overall chaotic, but there is a hint of quasi-periodicity.
GW radiation has no interesting consequence, however, in the case of close
binaries, because of very tiny disk masses. GW radiation is not significant,
either, for AGN because of very slow rotation velocities. The most promising
case can be found in gamma-ray bursts or supernovae, in which a massive torus
(or disk) with a solar mass or so may be formed around a stellar-mass compact
object as the result of a merger of compact objects, or by the fallback of
exploded material towards the center in a supernova. Although much more intense
GW radiation is expected before the formation of the torus, the detection of GW
radiation in the subsequent accretion phase is of great importance, since it
will provide a good probe to investigating their central engines.Comment: To appear in PASJ, 15 pages, 2 figure
