Self-consistent MHD simulation of jet launching in a neutron star - white dwarf merger

Authors: Morán-Fraile, Javier; Röpke, Friedrich K.; Pakmor, Rüdiger; Aloy, Miguel A.; Ohlmann, Sebastian T.; Schneider, Fabian R. N.; Leidi, Giovanni;

Abstract:

The merger of a white dwarf (WD) and a neutron star (NS) is a relatively common event that will produce an observable electromagnetic signal. Furthermore, the compactness of these stellar objects makes them an interesting candidate for gravitational wave (GW) astronomy, potentially being in the frequency range of LISA and other missions. To date, three-dimensional simulations of these mergers have not fully modelled the WD disruption, or have used lower resolutions and have not included magnetic fields even though they potentially shape the evolution of the merger remnant. In this work, we simulate the merger of a 1.4M_\odot NS with a 1M_\odot carbon oxygen WD in the magnetohydrodynamic moving mesh code AREPO. We find that the disruption of the WD forms an accretion disk around the NS, and the subsequent accretion by the NS powers the launch of strongly magnetized, mildly relativistic jets perpendicular to the orbital plane. Although the exact properties of the jets could be altered by unresolved physics around the NS, the event could result in a transient with a larger luminosity than kilonovae. We discuss possible connections to fast blue optical transients (FBOTs) and long-duration gamma-ray bursts. We find that the frequency of GWs released during the merger is too high to be detectable by the LISA mission, but suitable for deci-hertz observatories such as LGWA, BBO or DECIGO.

Videos

3D volume rendering of the last 100s of the artificial orbit shrinking, disruption of the WD, and formation of the jet. For clarity, densities below 1000 g/cm^3 and velocities below 0.03c are fully transparent. The size of the neutron star has been scaled up so that it encompasses the volume where the gravitational potential has been softened. Accurate values for these magnitudes and others are shown in 2D slices in the additional material available at zenodo.