Galactic Interstellar Scintillation Observed from Four Globular Cluster Pulsars by FAST

TL;DR

This study uses FAST to detect interstellar scintillation arcs from globular cluster pulsars, revealing the locations of scattering media and providing new insights into the Milky Way's interstellar medium.

Contribution

First detection of scintillation arcs from globular cluster pulsars with FAST, mapping scattering screens and their positions relative to the galactic plane.

Findings

Scattering screens are located at several kiloparsecs from Earth.

Detected the most distant off-plane scattering screens to date.

Evidence suggests the Local Bubble boundary influences scattering.

Abstract

We report detections of scintillation arcs for pulsars in globular clusters M5, M13 and M15 for the first time using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). From observations of these arcs at multiple epochs, we infer that screen-like scattering medium exists at distances $4.1_{-0.3}^{+0.2}$ kpc, $6.7_{-0.2}^{+0.2}$ kpc and $1.3_{-1.0}^{+0.7}$ kpc from Earth in the directions of M5, M13 and M15, respectively. This means M5's and M13's scattering screens are located at $3.0_{-0.2}^{+0.1}$ kpc and $4.4_{-0.1}^{+0.1}$ kpc above the galactic plane, whereas, M15's is at $0.6_{-0.5}^{+0.3}$ kpc below the plane. We estimate the scintillation timescale and decorrelation bandwidth for each pulsar at each epoch using the one-dimensional auto-correlation in frequency and time of the dynamic spectra. We found that the boundary of the Local Bubble may have caused the scattering of M15, and detected the most distant off-plane scattering screens to date through pulsar scintillation, which provides evidence for understanding the medium circulation in the Milky Way.