Multistation interstellar scintillation analysis of PSR B0655 + 64 with LOFAR

ABSTRACT

In this paper, we measure the scintillation of PSR B0655 + 64, a slow pulsar in a 24.7 h orbit with a white dwarf companion. We use data recorded simultaneously by four LOw-Frequency ARray stations over two long observations, of 12 and 16 h. We measure time delays of the scintillation pattern across different baselines, determine scintillation arc curvatures, and jointly model these quantities to infer orbital and scintillation parameters of the system. Assuming the scattering is dominated by a highly anisotropic screen, we find from the 16-h data set that its angle of anisotropy is well constrained, with the scattering points lying at a position angle of $178^\circ \pm 15^\circ$ (from N through E), located at a fractional distance of $0.23\pm 0.08$ from the pulsar, with velocity along the scattering points of $12\pm 7{\rm \, km\, s^{-1}}$. Using this, we obtain two degenerate solutions for the orbital inclination, $127^{\circ }\pm 19^{\circ }$ and $53^{\circ }\pm 19^{\circ }$, both with the same $\sin i$ and thus yielding the same constraint on the component masses. We also analyse the 12-h data set, finding that it shows evidence for a second scattering screen; this complicates scintillation arc measurements, but we use it as a consistency check for the model parameters obtained from the 16-h data set. Overall, our results show that with multistation scintillation measurements one can directly obtain properties of scintillation screens, and use these to determine orbital properties, although one has to be careful not to be misled by the effects of multiple screens.