Intermediate-Mass-Elements in Young Supernova Remnants Reveal Neutron Star Kicks by Asymmetric Explosions

摘要

The birth properties of neutron stars yield important information on thestill debated physical processes that trigger the explosion and on intrinsicneutron-star physics. These properties include the high space velocities ofyoung neutron stars with average values of several 100 km/s, whose underlying"kick" mechanism is not finally clarified. There are two competingpossibilities that could accelerate NSs during their birth: anisotropicejection of either stellar debris or neutrinos. We here present new evidencefrom X-ray measurements that chemical elements between silicon and calcium insix young gaseous supernova remnants are preferentially expelled opposite tothe direction of neutron star motion. There is no correlation between the kickvelocities and magnetic field strengths of these neutron stars. Our resultssupport a hydrodynamic origin of neutron-star kicks connected to asymmetricexplosive mass ejection, and they conflict with neutron-star accelerationscenarios that invoke anisotropic neutrino emission caused by particle andnuclear physics in combination with very strong neutron-star magnetic fields.