Interstellar scintillations of PSR B1919+21: space-ground interferometry

TL;DR

This study used space-ground interferometry to analyze interstellar scintillations of pulsar PSR B1919+21, revealing multiple scattering layers, a deflecting prism, and negligible ionospheric effects, advancing understanding of interstellar plasma distribution.

Contribution

First space-ground interferometric observation of pulsar scintillations revealing multiple scattering components and a deflecting prism near Earth.

Findings

Identified two scintillation components at different distances

Detected a deflecting prism near Earth affecting observations

Confirmed ionosphere does not impact space-ground baseline measurements

Abstract

We carried out observations of pulsar PSR B1919+21 at 324 MHz to study the distribution of interstellar plasma in the direction of this pulsar. We used the RadioAstron (RA) space radiotelescope together with two ground telescopes: Westerbork (WB) and Green Bank (GB). The maximum baseline projection for the space-ground interferometer was about 60000 km. We show that interstellar scintillation of this pulsar consists of two components: diffractive scintillations from inhomogeneities in a layer of turbulent plasma at a distance $z_{1} = 440$ pc from the observer or homogeneously distributed scattering material to pulsar; and weak scintillations from a screen located near the observer at $z_{2} = 0.14 \pm 0.05$ pc. Furthermore, in the direction to the pulsar we detected a prism that deflects radiation, leading to a shift of observed source position. We show that the influence of the ionosphere can be ignored for the space-ground baseline. Analysis of the spatial coherence function for the space-ground baseline (RA-GB) yielded the scattering angle in the observer plane: $\theta_{scat}$ = 0.7 mas. An analysis of the time-frequency correlation function for weak scintillations yielded the angle of refraction in the direction to the pulsar: $\theta_{ref, 0}$ = 110 ms and the distance to the prism $z_{prism} \le 2$ pc.