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

Yanqing Cai, Ziwei Wu, Weiwei Zhu, Joris P. W. Verbiest, Yulan Liu, Krishnakumar Moochickal Ambalappat, Marcus Brüggen, Benedetta Ciardi, Ralf-Jürgen Dettmar, Ziyao Fang, Qiuyang Fu, Matthias Hoeft, Jiawei Jin, Lars Künkel, Jörn Künsemöller, Caisong Liu, Lingqi Meng, Xueli Miao, Jiarui Niu, Rukiya Rejep, Dominik J. Schwarz, Golam M. Shaifullah, Caterina Tiburzi, Christian Vocks, Olaf Wucknitz, Mengyao Xue, Mao Yuan, Youling Yue, Chunfeng Zhang, Zhen Zhang

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$+$7429, carried out from 2013 September to 2023 September with the LOw-Frequency ARray (LOFAR) High Band Antennae in the frequency range of 120 - 170 MHz. We derive the basic scintillation parameters, scintillation bandwidth ($Δν_{\rm d}$) and scintillation timescale ($Δτ_{\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 $Δν_{\rm d}$ and $Δτ_{\rm d}$ for PSR J0814$+7429$, which shows a strong annual variation in the time series of the $Δτ_{\rm d}$. 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.

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

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 J08147429, 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 () and scintillation timescale (), 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 and for PSR J0814, which shows a strong annual variation in the time series of the . From our modeling of the annual variations of scintillation velocities, the scattering screen is anisotropic and located at kpc from the Earth, likely corresponding to the boundary of the Local Bubble.

Paper Structure

This paper contains 7 sections, 6 equations, 4 figures, 1 table.

Table of Contents

  1. Introduction
  2. Observations and data processing
  3. Results and Discussion
  4. Scintillation from a thin screen
  5. Fitting annual variations
  6. Conclusion
  7. Posterior probability distributions for the fitted parameters during MCMC

Figures (4)

  • Figure 1: Example dynamic spectrum of PSR J0814$+$7429 with LOFAR taken on MJD 57361. The white patches are removed due to RFI.
  • Figure 2: Long-term variations of scintillation timescale $\Delta \tau_{\rm d}$ (top panel) and scintillation bandwidth $\Delta \nu_{\rm d}$ (bottom panel) for PSR J0814$+$7429. The vertical gray dotted lines indicate the start of a calendar year. More observations in 2017 resulted in relatively dense data points this year.
  • Figure 3: Top panel: the scintillation velocities of PSR J0814$+$7429 as a function of day of year. The points with error bars are the scintillation velocities from Equation \ref{['exp1']}, and the curve shown is that from Equation \ref{['exp2']}. The residuals between the two scintillation velocities are shown in the bottom left panel. And the residual histogram distribution with Gaussian fitting (gray dashed line) is shown in the bottom right panel.
  • Figure 4: The posterior probability distributions of all fitted parameters. From left to right in each 1D histogram, three black dashed lines denote the 16% fractional percentiles, the most likely values, and the 84% fractional percentiles, respectively. The most likely values and the upper/lower errors are indicated at the top of the 1D histograms.