Possible early linear acceleration of proto-neutron stars via asymmetric neutrino emission in core-collapse supernovae. (arXiv:1907.04863v1 [astro-ph.HE])

Possible early linear acceleration of proto-neutron stars via asymmetric neutrino emission in core-collapse supernovae. (arXiv:1907.04863v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Nagakura_H/0/1/0/all/0/1">Hiroki Nagakura</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sumiyoshi_K/0/1/0/all/0/1">Kohsuke Sumiyoshi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yamada_S/0/1/0/all/0/1">Shoichi Yamada</a>

In this {it Letter}, we present the result of an axisymmetric CCSN
simulation conducted with appropriate treatments of neutrino transport and
proper motions of proto-neutron star (PNS), in which a remarkable PNS
acceleration is observed in association with asymmetric neutrino emissions by
the time of $300$ms after bounce. We find that these asymmetric neutrino
emissions play important roles in the acceleration of PNS in this phase. The
correlation between the PNS proper motion and the asymmetric ejecta is similar
to that in the neutron star (NS) kick of hydrodynamic origin. Both
electron-type neutrinos ($nu_{rm e}$) and their anti-particles
($bar{nu}_{rm e}$) have $sim 10%$ level of asymmetry between the northern
and southern hemispheres, while other heavy-leptonic neutrinos ($nu_x$) have
much smaller asymmetry of $sim 1 %$. The emissions of $bar{nu}_{rm e}$ and
$nu_x$ are higher in the hemisphere of stronger shock expansion whereas the
$nu_{rm e}$ emission is enhanced in the opposite hemisphere: in total the
neutrinos carry some linear momentum to the hemisphere of the stronger shock
expansion. The asymmetry is attributed to the non-spherical distribution of
electron-fraction ($Y_e$) in the envelope of PNS. Although it is similar to
LESA (lepton-emission self-sustained asymmetry), the $Y_e$ asymmetry seems to
be associated with the PNS motion: the latter triggers lateral circular motions
in the envelope of PNS by breaking symmetry of the matter distribution there,
which are then sustained by a combination of convection, lateral neutrino
diffusion and matter-pressure gradient. Our findings may have an influence on
the current theories on the NS kick mechanism although long-term simulations
are required to assess their impact on the later evolution.

In this {it Letter}, we present the result of an axisymmetric CCSN
simulation conducted with appropriate treatments of neutrino transport and
proper motions of proto-neutron star (PNS), in which a remarkable PNS
acceleration is observed in association with asymmetric neutrino emissions by
the time of $300$ms after bounce. We find that these asymmetric neutrino
emissions play important roles in the acceleration of PNS in this phase. The
correlation between the PNS proper motion and the asymmetric ejecta is similar
to that in the neutron star (NS) kick of hydrodynamic origin. Both
electron-type neutrinos ($nu_{rm e}$) and their anti-particles
($bar{nu}_{rm e}$) have $sim 10%$ level of asymmetry between the northern
and southern hemispheres, while other heavy-leptonic neutrinos ($nu_x$) have
much smaller asymmetry of $sim 1 %$. The emissions of $bar{nu}_{rm e}$ and
$nu_x$ are higher in the hemisphere of stronger shock expansion whereas the
$nu_{rm e}$ emission is enhanced in the opposite hemisphere: in total the
neutrinos carry some linear momentum to the hemisphere of the stronger shock
expansion. The asymmetry is attributed to the non-spherical distribution of
electron-fraction ($Y_e$) in the envelope of PNS. Although it is similar to
LESA (lepton-emission self-sustained asymmetry), the $Y_e$ asymmetry seems to
be associated with the PNS motion: the latter triggers lateral circular motions
in the envelope of PNS by breaking symmetry of the matter distribution there,
which are then sustained by a combination of convection, lateral neutrino
diffusion and matter-pressure gradient. Our findings may have an influence on
the current theories on the NS kick mechanism although long-term simulations
are required to assess their impact on the later evolution.

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