Precision Determination of Scintillation Screen Parameters from Annual Modulation Measurement of Pulsar Scintillation Arc Curvature with the FAST Telescope

TL;DR

This study tackles the long-standing challenge of determining scintillation-screen distances by leveraging annual modulation of scintillation-arc curvature measured with FAST. The authors develop and apply a theoretical framework linking arc curvature to screen distance, orientation, and velocity through quantities like $\eta_{\nu}$ and $f_{\eta}$, accounting for isotropic (1D) and anisotropic (2D) scattering regimes. By analyzing multiple epochs of pulsars B1237+25, B1842+14, and B2021+51, they derive precise screen distances, discovering that several screens lie near the Local Bubble boundary and that screens are distributed along the full Earth–pulsar sightlines. The results provide a substantial, high-signal sample of scintillation-screen measurements, revealing rich plasma-density fluctuation structures in the Milky Way and enabling improved mapping of the IISM.

Abstract

Pulsar scintillation observations have revealed ubiquitous discrete scintillation screens in the interstellar medium. A major obstacle in identifying the nature of these screens is the uncertainty in their distances, which prevents precise correlation with known structures in the Milky Way. We used the Five-hundred-meter Aperture Spherical radio Telescope (FAST) to observe PSR B1237+25, PSR 1842+14, and PSR 2021+51. We detected 10 scintillation arcs in PSR B1237+25, 1 in PSR 1842+14, and at least 6 in PSR 2021+51. By modeling the annual modulation of these scintillation arcs, we constrained the distances of the scintillation screens, as well as the anisotropic scattering directions and the projected velocities in those directions. The scintillation screens are distributed throughout the entire paths between Earth and the pulsars. Among these, the distance to the main scintillation screen toward PSR B1237+25 is $267^{+32}_{-28}$ pc, the scintillation screen toward PSR B1842+14 is at a distance of $240^{+210}_{-120}$ pc, and the main scintillation screen toward PSR B2021+51 is located at $887^{+167}_{-132}$ pc. Several screens in our sample appear at distances coinciding with the Local Bubble boundary, particularly the brightest scintillation arc toward PSR B1237+25. We provide a substantial sample of scintillation screen measurements, revealing the rich plasma density fluctuation structures present in the Milky Way.

Figures (1)

• Figure 1: Transverse velocity of the pulsar $\mathbf{v}_{\text{psr}}$ (red arrow) and the projected Earth’s velocity $\mathbf{v}_{\text{Earth}}(t)$ (black ellipse) for the three pulsars.