Low-frequency spectra and scattering of pulsars towards the Gum Nebula with the MWA
Abstract
Context. The Gum Nebula is a nearby ionised complex with sight-line-dependent pulsar propagation. Aims. We test whether a smooth ionised structure can explain low-frequency spectral turnovers and pulse broadening, or whether smaller-scale material is required. Methods. We analysed Murchison Widefield Array observations of six pulsars at 80--240 MHz, combining sub-band flux densities with literature data. We compared power-law, free--free absorption (FFA), and turnover-constrained broken-power-law (BPL) spectra, and modelled scattering through pulse-profile convolution. PSR J0820-4114 and the Vela pulsar were fitted jointly across frequency. Results. All six spectra depart from a single power law. FFA is favoured for PSRs J0737-3039A and J0820-4114, and BPL for J0742-2822 and J0835-4510; the other two classifications depend on assumed error floors. Conditional FFA solutions imply emission measures of 104--105 pc cm−6 for electron temperatures of 3×103--104 K, far exceeding smooth-shell expectations. PSRs J0737-3039A and J0837-4135 have scattering laws consistent with τsc∝ν−4. We obtain αsc=−3.07±0.11 for J0742-2822 and −1.59±0.44 for J0820-4114 using a joint two-component model. The Vela pulsar is best described by an effective thick-screen model with αsc≃−2.74. Neither tested Galactic electron-density model reproduces both independent distances and low-frequency scattering uniformly. Conclusions. The results favour a structured Gum--Vela magneto-ionic environment in which neighbouring sight lines probe different absorbing and scattering material; these effects need not arise in the same plasma component.
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BibTeX
@misc{yu2026lowfrequency,
title = {{Low-frequency spectra and scattering of pulsars towards the Gum Nebula with the MWA}},
author = {Ting Yu and Zhifu Gao and Zhongli Zhang and Weicong Jing},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.18146},
eprint = {2610.18146},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.18146},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Low-frequency spectra and scattering of pulsars towards the Gum Nebula with the MWA
AU - Ting Yu
AU - Zhifu Gao
AU - Zhongli Zhang
AU - Weicong Jing
PY - 2026
DA - 2026/10/13
PB - arXiv
DO - 10.48550/arxiv.2610.18146
UR - https://arxiv.org/abs/2610.18146
AB - Context. The Gum Nebula is a nearby ionised complex with sight-line-dependent pulsar propagation. Aims. We test whether a smooth ionised structure can explain low-frequency spectral turnovers and pulse broadening, or whether smaller-scale material is required. Methods. We analysed Murchison Widefield Array observations of six pulsars at 80--240 MHz, combining sub-band flux densities with literature data. We compared power-law, free--free absorption (FFA), and turnover-constrained broken-power-law (BPL) spectra, and modelled scattering through pulse-profile convolution. PSR J0820-4114 and the Vela pulsar were fitted jointly across frequency. Results. All six spectra depart from a single power law. FFA is favoured for PSRs J0737-3039A and J0820-4114, and BPL for J0742-2822 and J0835-4510; the other two classifications depend on assumed error floors. Conditional FFA solutions imply emission measures of 10^4--10^5 pc cm^−6 for electron temperatures of 3×10^3--10^4 K, far exceeding smooth-shell expectations. PSRs J0737-3039A and J0837-4135 have scattering laws consistent with τ_sc∝ν^−4. We obtain α_sc=−3.07±0.11 for J0742-2822 and −1.59±0.44 for J0820-4114 using a joint two-component model. The Vela pulsar is best described by an effective thick-screen model with α_sc≃−2.74. Neither tested Galactic electron-density model reproduces both independent distances and low-frequency scattering uniformly. Conclusions. The results favour a structured Gum--Vela magneto-ionic environment in which neighbouring sight lines probe different absorbing and scattering material; these effects need not arise in the same plasma component.
ER -