Propagation of magnetized neutron stars through the interstellar medium

This work investigates the propagation of magnetized, isolated old neutron stars through the interstellar medium (ISM). We performed axisymmetric, non relativistic magnetohydrodynamic (MHD) simulations of the propagation of a nonrotating star with a dipole magnetic fid aligned with its velocity throu gh the ISM. Effects of rotation will be discussed in a subsequent work. We consider two cases : (1) where the accretion radius R-acc is comparable to the magnetic standoff distance or Alfven radius R-A and gravitational focus ing is important and (2) where R-acc << R-A and the magnetized star interac ts with the ISM as a "magnetic plow," without significant gravitational foc using. For the first case, simulations were done at a low Mach number M = 3 for a range of values of the magnetic field B-*. For the second case, simu lations were done for higher Mach numbers, M = 10, 30, and 50. In both case s, the magnetosphere of the star represents an obstacle for the flow, and a shock wave stands in front of the star. Magnetic field lines are stretched downwind from the star and form a hollow elongated magnetotail. Reconnecti on of the magnetic field is observed in the tail, which may lead to the acc eleration of particles. Similar powers are estimated to be released in the bow shock wave and in the magnetotail. The estimated powers are, however, b elow present detection limits. Results of our simulations may be applied to other strongly magnetized stars, for example, white dwarfs and magnetic Ap stars. Future more sensitive observations may reveal bow shocks and long m agnetotails of magnetized stars moving through the ISM.