Astron. Astrophys. 317, 140-163 (1997)
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Gravitational radiation from convective instabilities
in Type II supernova explosions
Ewald Müller and
Max-Planck-Institut für Astrophysik,
Karl-Schwarzschild-Str. 1, D-85740 Garching, Germany
Received 5 February 1996 / Accepted 23 April 1996
We present two- and three-dimensional simulations of convective
instabilities during the first second of a Type II supernova
explosion. Convective overturn occurs in two distinct, spatially well
separated regions: (i) inside the proto-neutron star immediately below
the neutrinosphere (
) and (ii) in the neutrino-heated "hot-bubble"
region interior to the outward propagating revived shock wave (
). We have calculated the gravitational wave
signature of both convective instabilities including the quadrupole
waveforms, the energy spectra, and the total amount of the emitted
gravitational wave energy. Moreover, we have estimated the amplitude
and energy of gravitational waves associated with the anisotropic
neutrino emission that is caused by the convective transport of
neutrinos and by aspherical perturbations of temperature and density
in the neutrinospheric region.
For a supernova located at a distance of 10 kpc the maximum
dimensionless gravitational wave amplitudes due to convective mass
motions range from
for the three-dimensional simulation to
for the most strongly radiating two-dimensional
model. The total emitted energy varies from
. The convective mass motions inside the
proto-neutron star produce a stronger signal than convection in region
(ii) with up to a factor of 10 larger amplitudes and 1000 times more
gravitational wave energy. Because of smaller convective eddies and
structures and slower overturn velocities, the wave amplitudes of
three-dimensional models are more than a factor of 10 smaller, and the
energy emitted in gravitational waves is almost 3 orders of magnitude
less than in the corresponding two-dimensional situation.
In two dimensions the gravitational wave amplitude associated with
the anisotropic emission of neutrinos can be larger (factor 5) than
the wave amplitude due to mass motions in the proto-neutron star,
although the energy in the neutrino tidal field is 20 times smaller.
In three dimensions the neutrino gravitational wave amplitude is
reduced by a factor of about 10 and the gravitational wave energy by a
factor of roughly 100 relative to the two-dimensional results.
Nevertheless, the neutrino tidal field is more than a factor of 10
larger than the gravitational wave amplitude from mass motions and the
corresponding gravitational wave energies can be of similar size.
Most of the gravitational radiation from convection inside the
proto-neutron star is emitted in the frequency band 100-1000 Hz, while
convective motions in the hot-bubble region generate waves from
several 100 Hz down to a few Hz. Gravitational waves from the
anisotropic neutrino emission have most power at frequencies between
some 10 Hz and a few 100 Hz and a low-frequency contribution at about
1 Hz to several Hz.
Features in the gravitational-wave signal from the neutrino-heated
region are well correlated with structures in the neutrino signal,
both being associated with sinking and rising lumps of matter and with
temporal variations of aspherical accretion flows towards the
proto-neutron star. A simultaneous measurement of both signals would
impose important constraints on the dynamics of Type II supernovae and
theoretical models of the explosion mechanism.
Key words: supernovae:
Send offprint requests to: E. Müller
© European Southern Observatory (ESO) 1997