RadioAstron space-ground very long baseline interferometry observations of the pulsar B0950+08, conducted with the 10 m Space Radio Telescope in conjunction with the Arecibo 300 m telescope and the Westerbork Synthesis Radio Telescope at a frequency of 324 MHz were analyzed in order to investigate plasma inhomogeneities in the direction of this nearby pulsar. The observations were conducted at a spacecraft distance of 330, 000 km, resulting in a projected baseline of 220, 000 km, providing the greatest angular resolution ever achieved at meter wavelengths. Our analysis is based on fundamental behavior of structure and coherence functions. We find that the pulsar shows scintillation on two frequency scales, both much less than the observing frequency, but modulation is less than 100%. We infer that the scattering is weak, but a refracting wedge disperses the scintillation pattern. The refraction angle of this "cosmic prism" is measured as θ0 = 1.1-4.4 mas, with the refraction direction being approximately perpendicular to the observer velocity. We show that the observed parameters of scintillation effects indicate that two plasma layers lie along the line of sight to the pulsar, at distances of 4.4-16.4 pc and 26-170 pc, and traveling in different directions relative to the line of sight. Spectra of turbulence for the two layers are found to follow a power law with the indices γ1 = γ2 = 3.00 ± 0.08, significantly different from the index expected for a Kolmogorov spectrum of turbulence, γ = 11/3.

We discovered fine-scale structure within the scattering disk of PSR B0329+54 in observations with the RadioAstron ground-space radio interferometer. Here, we describe this phenomenon, characterize it with averages and correlation functions, and interpret it as the result of decorrelation of the impulse-response function of interstellar scattering between the widely-separated antennas. This instrument included the 10-m Space Radio Telescope, the 110-m Green Bank Telescope, the 14x25-m Westerbork Synthesis Radio Telescope, and the 64-m Kalyazin Radio Telescope. The observations were performed at 324 MHz, on baselines of up to 235,000 km in November 2012 and January 2014. In the delay domain, on long baselines the interferometric visibility consists of many discrete spikes within a limited range of delays. On short baselines it consists of a sharp spike surrounded by lower spikes. The average envelope of correlations of the visibility function show two exponential scales, with characteristic delays of $\tau_1=4.1\pm 0.3\ \mu{\rm s}$ and $\tau_2=23\pm 3\ \mu{\rm s}$, indicating the presence of two scales of scattering in the interstellar medium. These two scales are present in the pulse-broadening function. The longer scale contains 0.38 times the scattered power of the shorter one. We suggest that the longer tail arises from highly-scattered paths, possibly from anisotropic scattering or from substructure at large angles.