A possible mechanism for magnetar soft X-ray/γ-ray emission

Abstract

Once the energies of electrons near the Fermi surface obviously exceed the threshold energy of the inverse β decay, electron capture (EC) dominates inside the magnetar. Since the maximal binding energy of the 3P2 neutron Cooper pair is only about 0.048 MeV, the outgoing high-energy neutrons (Ek(n) > 60 MeV) created by the EC can easily destroy the 3P2 neutron Cooper pairs through the interaction of nuclear force. In the anisotropic neutron superfluid, each 3P2 neutron Cooper pair has magnetic energy 2μnB in the applied magnetic field B, where μn = 0.966 × 10−23 erg·G−1 is the absolute value of the neutron abnormal magnetic moment. While being destroyed by the high-energy EC neutrons, the magnetic moments of the 3P2 Cooper pairs are no longer arranged in the paramagnetic direction, and the magnetic energy is released. This released energy can be transformed into thermal energy. Only a small fraction of the generated thermal energy is transported from the interior to the surface by conduction, and then it is radiated in the form of thermal photons from the surface. After highly efficient modulation within the star's magnetosphere, the thermal surface emission is shaped into a spectrum of soft X-rays/γ-rays with the observed characteristics of magnetars. By introducing related parameters, we calculate the theoretical luminosities of magnetars. The calculation results agree well with the observed parameters of magnetars.