Interstellar scintillation and polarization of PSR B0656+14 in the Monogem Ring

TL;DR

This study uses FAST radio telescope observations to analyze interstellar scintillation and polarization of PSR B0656+14, revealing two distinct scattering regions associated with the Monogem Ring and Local Bubble, and providing insights into the scattering irregularities and pulsar geometry.

Contribution

It identifies and characterizes two separate scattering regions affecting PSR B0656+14, confirming the Monogem Ring association and analyzing their anisotropy and spatial spectra.

Findings

Two scattering regions identified, associated with Monogem Ring and Local Bubble.

Scattering screens located approximately 28 pc and 185 pc from the pulsar and Earth.

Scattering irregularities are mildly anisotropic with a flatter-than-Kolmogorov spectrum.

Abstract

High sensitivity interstellar scintillation and polarization observations of PSR~B0656+14 made at three epochs over a year using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) show that the scattering is dominated by two different compact regions. We identify the one nearer to the pulsar with the shell of the Monogem Ring, thereby confirming the association. The other is probably associated with the Local Bubble. We find that the observed position angles of the pulsar spin axis and the space velocity are significantly different, with a separation of $19\fdg3\pm$0\fdg8, inconsistent with a previously published near-perfect alignment of $1\degr\pm 2\degr$. The two independent scattering regions are clearly defined in the secondary spectra which show two strong forward parabolic arcs. The arc curvatures imply that the scattering screens corresponding to the outer and inner arcs are located approximately 28~pc from PSR B0656+14 and 185~pc from the Earth, respectively. Comparison of the observed Doppler profiles with electromagnetic simulations shows that both scattering regions are mildly anisotropic. For the outer arc, we estimate the anisotropy $A_R$ to be approximately 1.3, with the scattering irregularities aligned parallel to the pulsar velocity. For the outer arc, we compare the observed delay profiles with delay profiles computed from a theoretical strong-scattering model. Our results suggest that the spatial spectrum of the scattering irregularities in the Monogem Ring is flatter than Kolmogorov, but further observations are required to confirm this.