Double-lens Scintillometry: The variable scintillation of pulsar B1508+55

Abstract

We report on observations of PSR B1508+55's scintillation at the Effelsberg 100-m telescope spanning from early 2020 to early 2022. In the autumn of 2020, close to the time the pulsar was predicted by Wucknitz (2018) to cross echoes in its pulse profile, a sudden transition in the scintillation arcs from peculiar stripe-like features to parabolic arclets was observed. To infer a geometric model of the scattering we measure the effects of the annual velocity curve of Earth, of the relative movement of the line of sight, and of the projection of points on a second scattering screen and develop novel methods to do so. The latter phenomenon was discovered by this study and strongly indicates a two-screen scattering geometry. We derive an analytical two-screen model and demonstrate in a Markov Chain Monte Carlo analysis as well as simulations that it can be successfully applied to explain the observations by interpreting the transition as a change of relative amplitudes of images as well as a shift in the orientation of anisotropy. The collection of methods we demonstrate here is transferable to other pulsars with the potential to strongly improve constraints on scattering models.

A Scintillation Arc Survey of 22 Pulsars with Low to Moderate Dispersion Measures

“…The scattering geometry is complex for this pulsar, as documented by Bansal et al (2020), who observed remarkable echoes of the pulse arriving 30 ms after the main pulse at 50 and 80 MHz that persisted over about 3 years. Also see Sprenger et al (2022) who develop a two-screen explanation for the scattering from this pulsar. Arc credibility indices η cred : 340 MHz, 825 MHz, 1400 MHz (2, 2, 2)…”

H-FISTA: a hierarchical algorithm for phase retrieval with application to pulsar dynamic spectra

“…This provides us with 𝑁/2 complex constraints, in addition to the 𝑁 real data constraints, resulting in exactly as many constraints as unknowns -barely sufficient to obtain a solution even in the case of zero measurement noise. If it happens that the scattering takes place in only one plane on the sky then our solution space need only be one-dimensional, and in this situation the model wavefield is very tightly constrained by the twodimensional dataset (Baker et al 2022;Sprenger et al 2022). In the more general case of a two-dimensional scattered image we need to impose additional, strong restrictions on the solution.…”