Correlation of the scattering and dispersion events in the Crab Nebula pulsar

TL;DR

This study observed correlated scattering and dispersion variations in the Crab pulsar over 200 days, attributing these to an ionized cloud crossing the line of sight, revealing insights into the nebula's intervening medium.

Contribution

It provides the first detailed correlation analysis of scattering and dispersion events in the Crab pulsar, linking them to a specific ionized cloud crossing the line of sight.

Findings

Simultaneous increase in scattering and dispersion measures during the event.

Estimated size and electron density of the intervening cloud.

Possible origin of turbulence within the cloud or from a separate filament.

Abstract

In separate series of observations of the Crab pulsar, pulse broadening due to scattering was measured at 111 MHz, and variations of dispersion due to pulse delay were measured at higher radio frequencies. In a remarkable event lasting 200 days a large increase occurred in both parameters and with similar time signatures. The increases in scattering and dispersion measure observed over the 200 days MJD 53950 - 54150 are attributable to the effects of an ionised cloud or filament crossing the line of sight. The cloud would be $10^11 - 10^12 m across, with electron density 10^3 - 10^4 cm^-3. The increased scattering might originate within the cloud itself, or the moving filament might induce turbulence in a separate higher density cloud in the line of sight.