Pulsar scintillation studies with LOFAR III. Annual variations in PSR~J0814$+$7429

TL;DR

This study uses LOFAR data over a decade to analyze long-term interstellar scintillation variations in pulsar PSR J0814+7429, revealing annual changes and the scattering screen's properties.

Contribution

It provides the first detailed long-term monitoring of scintillation parameters for PSR J0814+7429, identifying anisotropic scattering and local interstellar medium features.

Findings

Detected strong annual variation in scintillation timescale.

Estimated the scattering screen is at 0.23 kpc, near the Local Bubble boundary.

Confirmed anisotropic scattering properties of the interstellar medium.

Abstract

The interstellar scintillation observed in radio pulsars arises from interference between electromagnetic waves scattered by electron density fluctuations in the turbulent interstellar plasma, providing a critical tool for probing the small-scale structure of the ionized interstellar medium and the pulsar system itself. The primary aim of this work is to study long-term scintillation variations for a bright and nearby pulsar, PSR J0814$+$7429, carried out from 2013 September to 2023 September with the LOw-Frequency ARray (LOFAR) High Band Antennae in the frequency range of 120 - 170 MHz. We derive the basic scintillation parameters, scintillation bandwidth ($\Delta\nu_{\rm d}$) and scintillation timescale ($\Delta\tau_{\rm d}$), from the two-dimensional (2D) auto-covariance function of the dynamic spectra that are a 2D matrix of pulse intensity as a function of time and frequency. We present the long-term monitoring of $\Delta\nu_{\rm d}$ and $\Delta\tau_{\rm d}$ for PSR J0814$+7429$, which shows a strong annual variation in the time series of the $\Delta\tau_{\rm d}$. From our modeling of the annual variations of scintillation velocities, the scattering screen is anisotropic and located at $0.23\pm0.02$ kpc from the Earth, likely corresponding to the boundary of the Local Bubble.