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Role of nuclear physics in oscillations of magnetars

Abstract : Strong magnetic fields have important effects on the crustal properties of magnetars. Here we study the magnetoelastic oscillations of magnetars, taking into consideration the effect of strong magnetic fields on the crustal composition (magnetized crust). We calculate global magnetoelastic (GME) modes as well as modes confined to the crust (CME) only. The ideal magnetohydrodynamics is adopted for the calculation of magnetoelastic oscillations of magnetars with dipole magnetic fields. The perturbation equations obtained in general relativity using Cowling approximation are exploited here for the study of magnetoelastic oscillations. Furthermore, deformations due to magnetic fields and rotations are neglected in the construction of equilibrium models for magnetars. The composition of the crust directly affects its shear modulus, which we calculate using three different nucleon-nucleon interactions: SLy4, SkM, and Sk272. The shear modulus of the crust is found to be enhanced in strong magnetic fields ≥1017 G for all those Skyrme interactions. It is noted that the shear modulus of the crust for the SLy4 interaction is much higher than those of the SkM and Sk272 interactions in presence of magnetic fields or not. Though we do not find any appreciable change in frequencies of fundamental GME and CME modes with and without magnetized crusts, frequencies of first overtones of CME modes are significantly affected in strong magnetic fields ≥1017 G. However, this feature is not observed in frequencies of first overtones of GME modes. As in earlier studies, it is also noted that the effects of crusts on frequencies of both types of magnetoelastic modes disappear when the magnetic field reaches the critical field (B>4×1015 G). Frequencies of GME and CME modes calculated with magnetized crusts based on all three nucleon-nucleon interactions, stellar models and magnetic fields, are compared with frequencies of observed quasiperiodic oscillations (QPOs) in SGR 1806-20 and SGR1900+14. As in earlier studies, this comparison indicates that GME modes are essential to explain all the frequencies, as CME modes can explain only the higher frequencies.
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Submitted on : Thursday, September 1, 2016 - 4:29:33 PM
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R. Nandi, P. Char, D. Chatterjee, D. Bandyopadhyay. Role of nuclear physics in oscillations of magnetars. Physical Review C, American Physical Society, 2016, 94 (2), ⟨10.1103/PhysRevC.94.025801⟩. ⟨in2p3-01359053⟩



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