Scintillating insights into PSR J0737−3039A and the interstellar plasma of the Gum Nebula from MeerKAT

ABSTRACT The double pulsar system PSR J0737−3039A/B has enabled some of the most precise tests of strong-field gravity to date. Here, we present a scintillation analysis of the system based on an 18-month observation campaign with the MeerKAT radio telescope. The pulsar radiation shows flux density variations caused multipath scattering, which results in an interference pattern that varies in frequency and time. We characterize this interference pattern to infer properties of scattering plasma and the orbital geometry of the system. Our preferred model supports a scattering screen located at a distance of $D_s = 360^{+30}_{-40}$ pc. This moderately anisotropic screen of ionized gas (axial ratio $A_R = 2.4 \pm 0.2$) lies near the edge of the Gum Nebula, which is believed to be a supernova remnant (SNR) or an H${\small II}$1.2ex region. We estimate the expansion velocity of the nebula to be $V_{\textrm {s}} = 35 \pm 5$ km s$^{-1}$, implying an SNR age of $t \approx 1$ Myr. We also constrain the orbital orientation and inclination sense of the double pulsar to be $\Omega = 40^{\circ } \pm 3^{\circ }$ and $i > 90^{\circ }$, respectively. Assuming standard scattering geometry, our model yields a distance estimate consistent with the parallax-derived value of $D = 770 \pm 70$ pc from very long baseline interferometry. We conclude by discussing how future models of pulsar scintillation can enhance our understanding of the ionized interstellar medium and the properties of pulsars embedded within or lying behind such intervening structures.