Neutrino Transport in Strongly Magnetized Proto-Neutron Stars and the Origin of fast Spinning Pulsar Kicks
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Date
2013-06
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Addis Ababa University
Abstract
The Fermi LAT collaboration has recently reported the discovery of the pul-
sations of the
-ray pulsar J1823-3021A with a luminosity which is the highest
observed to date for any millisecond pulsar (MSP). This large luminosity implies
a large spin down rate _P and therefore a large magnetic eld which seems to be
incompatible with the observed short rotation period P . In proto-neutron stars
with strong magnetic elds, the cross section for e ( e) absorption on neutrons
(protons) depends on the local magnetic eld strength resulting from the quantiza-
tion of energy levels for the e (e+) produced in the nal state. If the neutron star
possesses an asymmetric magnetic eld topology in the sense that the magnitude
of magnetic eld in the north pole is di erent from that in the south pole, then
asymmetric neutrino emission may be generated. We calculate the absorption
cross sections of e and e in strong magnetic elds as a function of the neutrino
energy. These cross sections exhibit oscillatory behaviors that occur because new
Landau levels for the e (e+) become accessible as the neutrino energy increases.
By evaluating the appropriately averaged neutrino opacities, we demonstrate that
the change in the local neutrino
ux caused by the modi ed opacities is rather
small. To generate appreciable kick velocity ( 300 km s1) to the newly formed
neutron star, the di erence between the eld strengths at the two opposite poles
of the star must be at least 1016 G. We also consider the magnetic eld e ect
on the spectral neutrino energy
uxes. The oscillatory features in the absorption
opacities give rise to modulations in the emergent spectra of e and e