Tiny-scale Properties within the Interstellar Medium toward PSR J1644−4559. I. Observational Evidence of Turbulence-induced Tiny-scale Atomic Structures

Abstract We investigated H i absorption toward a single pulsar, PSR J1644−4559, and its variability over timescales from days to years, using Murriyang, CSIRO’s Parkes Radio Telescope. Our 19 epochs of spectral observations, spanning 1.2 yr with intervals as short as 1 day, provide the most comprehensive cadence coverage for monitoring H i absorption to date. We identified two significant detections of tiny-scale atomic structure (TSAS) with spatial scales ranging from a lower limit of ∼11 au to an upper limit of 165 au, both exhibiting integrated signal-to-noise ratios exceeding 5.0. We find a relationship between linear size and optical depth variation in the cold neutral medium (CNM) component hosting the TSAS, described by a power-law relationship, Δ τ int = Δ τ 0 (Δ L ) ( α −2)/2 , with α = 4.1 ± 0.4. This is the first observational evidence explicitly connecting TSAS to turbulence in CNM. This power-law index is significantly steeper than previously reported values for the CNM, where α ranges from 2.3 to 2.9, but similar to those observed in the warm ionized gas. Additionally, we observe no significant variation in α across the entire range of spatial scales traced in our study, indicating that turbulence may be cascading down and dissipating at smaller scales. While there is no precise proper-motion measurement for this pulsar, our estimates for the turbulence dissipation in the CNM place the lower and upper limits at less than 0.03 au and 0.4 au, respectively.

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Publication Details

Journal
The Astrophysical Journal Supplement Series
Published
2025-04-23
DOI
https://doi.org/10.3847/1538-4365/adbe66
Primary Topic
Astrophysics and Star Formation Studies
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article
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article

Tiny-scale Properties within the Interstellar Medium toward PSR J1644−4559. I. Observational Evidence of Turbulence-induced Tiny-scale Atomic Structures

Ningyu Tang, Snežana Stanimirović, S. Mader, J. M. Weisberg et al.
The Astrophysical Journal Supplement Series
Astrophysics and Star Formation Studies
article

Tiny-scale Properties within the Interstellar Medium toward PSR J1644−4559. I. Observational Evidence of Turbulence-induced Tiny-scale Atomic Structures

Ningyu Tang, Snežana Stanimirović, S. Mader, J. M. Weisberg, Lawrence Toomey, Yi Feng, J. R. Dawson, S. Johnston, Mengyao Xue, Donghui Quan, Chao‐Wei Tsai, Gan Luo, Shi Dai, Mengting Liu, G. Hobbs, Siyao Xu, Lei Zhang, Pei Zuo, Kai Zhang, Di Li, Pei Wang, James Green, Chenchen Miao, A. Kaushik
article en

Abstract

Abstract We investigated H i absorption toward a single pulsar, PSR J1644−4559, and its variability over timescales from days to years, using Murriyang, CSIRO’s Parkes Radio Telescope. Our 19 epochs of spectral observations, spanning 1.2 yr with intervals as short as 1 day, provide the most comprehensive cadence coverage for monitoring H i absorption to date. We identified two significant detections of tiny-scale atomic structure (TSAS) with spatial scales ranging from a lower limit of ∼11 au to an upper limit of 165 au, both exhibiting integrated signal-to-noise ratios exceeding 5.0. We find a relationship between linear size and optical depth variation in the cold neutral medium (CNM) component hosting the TSAS, described by a power-law relationship, Δ τ int = Δ τ 0 (Δ L ) ( α −2)/2 , with α = 4.1 ± 0.4. This is the first observational evidence explicitly connecting TSAS to turbulence in CNM. This power-law index is significantly steeper than previously reported values for the CNM, where α ranges from 2.3 to 2.9, but similar to those observed in the warm ionized gas. Additionally, we observe no significant variation in α across the entire range of spatial scales traced in our study, indicating that turbulence may be cascading down and dissipating at smaller scales. While there is no precise proper-motion measurement for this pulsar, our estimates for the turbulence dissipation in the CNM place the lower and upper limits at less than 0.03 au and 0.4 au, respectively.

The Astrophysical Journal Supplement SeriesVol. 278(1)
Commonwealth Scientific and Industrial Research Organisation (AU), Australia Telescope National Facility (AU), University of Wisconsin–Madison (US), Carleton College (US), Chinese Academy of Sciences (CN), Beijing Normal University (CN), Institute for Advanced Study (US), Institut de Radioastronomie Millimétrique (FR), Zhejiang Lab (CN), Kensington Health (CA), Astronomy and Space (AU), National Astronomical Observatories (CN), Anhui Normal University (CN), Swinburne University of Technology (AU), Zhejiang University (CN), Macquarie University (AU), Tsinghua University (CN)
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Astrophysics and Star Formation Studies
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