Scintillation Properties of PSR B1133+16 Measured with Very Long Baseline Interferometry

TL;DR

This paper uses very long baseline interferometry to analyze scintillation arcs of PSR B1133+16, resolving multiple anisotropic scattering screens along the line of sight. By combining visibility and intensity secondary cross-spectra, the authors measure arc curvatures, phase gradients, and phase de-rotations to extract the screens’ orientations, effective distances, and transverse velocities; they identify three distinct screens at distances of approximately $140\pm30$, $180\pm20$, and $250\pm30$ pc, with the two nearer screens plausibly associated with the Local Bubble wall. The approach overcomes degeneracies inherent in single-dish scintillation studies and yields high-precision, epoch-independent screen parameters, advancing our understanding of ISM structure on parsec scales. The results have implications for mapping small-scale ISM in the solar neighborhood and demonstrate the power of VLBI-based scintillation analyses for multi-screen systems.

Abstract

The scintillation of pulsars reveals small-scale structure of the interstellar medium. A powerful technique for characterizing the scintillating structures (screens) combines analysis of scintillation arcs and very long baseline interferometry (VLBI). We present the results of a VLBI analysis of the scintillation arcs of PSR B1133+16 from simultaneous observations with Arecibo, VLA, Jodrell Bank, Effelsberg, and Westerbork. Three arcs appear in the data set, all of which appear consistent with being the result of very anisotropic scattering screens. We are able to measure their orientations on the sky, down to uncertainties of $5\arcdeg$ for the two stronger screens, and measure distances, of $140\pm30$, $180\pm20$, and $250\pm30{\rm\,pc}$, consistent with, but substantially more precise than what was inferred previously from annual modulation patterns in the scintillation. Comparing with the differential dust extinction with distance in this direction, the two nearer screens appear associated with the wall of the Local Bubble.

Figures (4)

• Figure 1: PSR B1133+16 dynamic and secondary spectra, based on the Arecibo observation. Left: Dynamic spectrum; Middle: Secondary spectrum, the Fourier transform of the dynamic spectrum. Right: Secondary spectrum with parabolae for the three visible arcs overlaid, with best-fit value and estimated uncertainty indicated by the solid line and shading, respectively. The excess power visible along the delay axis is due to remaining radio frequency interference (narrow in frequency and roughly constant in time), while that along the Doppler axis is due to pulse-to-pulse variations (narrow in time but roughly achromatic).
• Figure 2: Visibility secondary cross-spectra. Top: Phases and intensities for all baselines involving Arecibo (binned by a factor of 4 in $f_{\textrm{D}}$ and 8 in $\tau$). Parabolae for each arc for the best-fit arc curvature are overdrawn, with colours following the panels below. Bottom: Phase along the arc, determined by averaging the complex values along delay within a parabolic region around each arc of width $0.58{\rm\,mHz}$. Grey points indicate all measured values, while black ones indicate the ones used for fitting gradients. The best fit is shown with coloured lines, with the uncertainties represented by the surrounding shaded regions.
• Figure 3: Intensity secondary cross-spectra. Arrangement is as for Figure \ref{['fig:visibility-cross-spectra']}.
• Figure 4: The mean power along parabolae of different curvatures of the Arecibo secondary spectrum (grey lines) using a range of bounds in doppler and delay. The vertical lines and shaded regions indicate the best fits and errors for the curvatures for the outer (green), middle (orange) and outer (blue) arcs.