2022ApJ...930..101R

Pulsar Hα bow shocks provide rare opportunities to constrain the energetics and kinematics of the relativistic pulsar wind. We have acquired optical imaging and integral field unit spectroscopy of the bow shock of the millisecond pulsar PSR J1959+2048, measuring the shock symmetry axis at a position angle = 213.2 ± 0.°2 and showing that this slow nonradiative shock has a broad-to-narrow line component ratio I_b/I_n = 4. The data show that the pulsar's velocity lies 2.°2 out of the plane of the sky. Coupled with a new fit for its timing proper motion, giving µ_tot = 30.05 mas yr^–1 and a Very Long Baseline Array (VLBA) interferometric parallax measurement giving d={2.57}_{-0.77}^{+1.84} kpc (90% range), we have unusually complete information on the pulsar kinematics. The bow shock constraints on the wind momentum flux imply that, at the best-fit parallax distance, the pulsar moment of inertia must be very large and/or the Hα efficiency at its modest shock velocity must be very high.