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arxiv: 2606.26745 · v1 · pith:UK5JUYECnew · submitted 2026-06-25 · 🌌 astro-ph.GA

SKA VLBI survey of the Southern sky for astrometry, geodesy, and astrophysics

M. H. Xu , L. Y. Petrov , Y. Y. Kovalev This is my paper

Pith reviewed 2026-06-26 04:22 UTC · model grok-4.3

classification 🌌 astro-ph.GA
keywords VLBISKASouthern skyastrometrygeodesycelestial reference frameextragalactic radio sourcesmulti-messenger astrophysics
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The pith

SKA will enable dedicated VLBI surveys of the Southern sky for geodesy and reference frames.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper establishes that the SKA will make possible VLBI surveys targeting the Southern sky, reaching sources invisible to northern radio telescopes. These surveys would support a southern-centered geodesy network, raise the density of compact calibrator sources, and extend the celestial reference frame southward. They would also deliver parsec-scale data on extragalactic sources needed for multi-messenger work with Cherenkov and neutrino telescopes plus joint VLBI-Gaia studies of active galaxies.

Core claim

The development of SKA will open the opportunity to run dedicated VLBI surveys of the Southern sky and observe sources not visible at radio telescopes located in the Northern hemisphere. These surveys will allow for doing geodesy with a Southern hemisphere-centered network, increase the density of compact radio sources that can be used as calibrators, further extend the celestial reference frame to deep south, and facilitate high-precision differential astrometry for a wide range of applications including supporting Cherenkov and neutrino telescope science cases as well as joint VLBI-Gaia studies of active galaxies.

What carries the argument

Dedicated southern VLBI surveys with the SKA that achieve deep completeness and measure parsec-scale properties of extragalactic radio sources.

Load-bearing premise

The SKA will be built and operated with the sensitivity, resolution, and scheduling flexibility required to reach deep completeness and parsec-scale measurements.

What would settle it

After SKA operations begin, southern VLBI source counts and completeness levels remain comparable to those already achievable with existing northern networks.

Figures

Figures reproduced from arXiv: 2606.26745 by L. Y. Petrov, M. H. Xu, Y. Y. Kovalev.

Figure 1
Figure 1. Figure 1: A Southern hemisphere centered network with SKA. At Tahiti site, indicated by a black dot, there is a plan to build a quad-band telescope as one of the geodetic stations while at the other sites radio telescopes are already available (either operating or under signal chain tests). be further extended to a development of a regional ionospheric model that will help to mitigate the impact of residual ionosphe… view at source ↗
read the original abstract

The development of SKA will open the opportunity to run dedicated VLBI surveys of the Southern sky and observe sources not visible at radio telescopes located in the Northern hemisphere. These surveys will allow for doing geodesy with a Southern hemisphere-centered network, increase the density of compact radio sources that can be used as calibrators, further extend the celestial reference frame to deep south, and facilitate high-precision differential astrometry for a wide range of applications. Achieving a deep completeness level and determining the parsec-scale properties of extragalactic radio sources is crucial for multi-wavelength and multi-messenger astrophysics. This includes supporting Cherenkov and neutrino telescope science cases, as well as joint VLBI-Gaia studies of active galaxies.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 0 minor

Summary. The manuscript proposes that the development of the SKA will enable dedicated VLBI surveys of the Southern sky to support geodesy with a Southern hemisphere-centered network, increase the density of compact radio calibrators, extend the celestial reference frame to the deep south, and facilitate high-precision differential astrometry for multi-wavelength and multi-messenger astrophysics applications including Cherenkov/neutrino science and joint VLBI-Gaia studies of active galaxies.

Significance. If the SKA delivers the necessary VLBI sensitivity, resolution, and scheduling flexibility, the proposed surveys would address a clear gap in Southern hemisphere coverage and provide tangible benefits for reference-frame maintenance and multi-messenger follow-up. The motivations align with established needs in radio astrometry and geodesy.

major comments (2)
  1. Abstract: the stated goals of achieving deep completeness and determining parsec-scale properties are presented without any sensitivity calculations, baseline requirements, or survey completeness estimates, which are load-bearing for assessing whether the listed applications can be realized.
  2. Abstract: the central premise is conditional on future SKA VLBI performance, yet no quantitative assessment of the required parameters (e.g., thermal noise, uv-coverage for parsec-scale imaging, or scheduling constraints) is supplied to support the feasibility of the geodesy and reference-frame claims.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their comments. We address the major points below and agree that revisions to the abstract are warranted to better reflect the scope and conditional nature of the proposal.

read point-by-point responses

  1. Referee: Abstract: the stated goals of achieving deep completeness and determining parsec-scale properties are presented without any sensitivity calculations, baseline requirements, or survey completeness estimates, which are load-bearing for assessing whether the listed applications can be realized.

    Authors: We agree that the abstract would be strengthened by acknowledging the absence of quantitative survey design elements. The manuscript is a high-level scientific motivation paper rather than a technical feasibility study; detailed sensitivity calculations and completeness estimates depend on finalized SKA VLBI configurations and are intended for subsequent dedicated papers. We will revise the abstract to clarify that the stated goals are contingent on achieving the required performance and to avoid implying that completeness estimates are already available. revision: yes

  2. Referee: Abstract: the central premise is conditional on future SKA VLBI performance, yet no quantitative assessment of the required parameters (e.g., thermal noise, uv-coverage for parsec-scale imaging, or scheduling constraints) is supplied to support the feasibility of the geodesy and reference-frame claims.

    Authors: We accept this criticism. The abstract does not provide the requested quantitative parameters because the paper focuses on scientific drivers rather than engineering specifications. We will revise the abstract to explicitly state that the proposed applications assume the SKA meets its target VLBI sensitivity, resolution, and operational flexibility, and we will add a short forward reference in the introduction to ongoing technical studies on these parameters. revision: yes

Circularity Check

0 steps flagged

No significant circularity

full rationale

The manuscript is a forward-looking survey proposal with no equations, derivations, fitted parameters, or load-bearing predictions. Its central claims are conditional on the external premise of SKA construction and performance; no internal chain reduces to self-definition, self-citation, or renaming of inputs. This is the most common honest finding for descriptive proposals.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

No free parameters, axioms, or invented entities appear in the abstract; the content is a high-level proposal for future observations.

pith-pipeline@v0.9.1-grok · 5662 in / 989 out tokens · 42749 ms · 2026-06-26T04:22:46.035023+00:00 · methodology

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Works this paper leans on

29 extracted references · 29 canonical work pages

  1. [1]

    doi: 10.1007/s00190-023-01738-w. J. M. Anderson and M. H. Xu.JGR-SE, 123(11):10,162–10,190,

    work page doi:10.1007/s00190-023-01738-w

  2. [2]

    doi: 10.3847/1538-4357/ab11c7. S. Duchesne et al.PASA, 42:38, Jan

    work page doi:10.3847/1538-4357/ab11c7

  3. [3]

    doi: 10.1017/pasa.2025.2. A. L. Fey et al.AJ, 127(3):1791–1795, Mar

    work page doi:10.1017/pasa.2025.2 2025

  4. [4]

    G.FichetdeClairfontaine,M.Perucho,J.M.Martí,andY.Y.Kovalev.A&A,693:A270,Jan.2025

    doi: 10.1086/381957. G.FichetdeClairfontaine,M.Perucho,J.M.Martí,andY.Y.Kovalev.A&A,693:A270,Jan.2025. doi: 10.1051/0004-6361/202451914. X. He et al.ASR, 76(10):5872–5889, Nov

    work page doi:10.1086/381957 2025

  5. [5]

    doi: 10.1016/j.asr.2025.08.036. L. Kern, H. Krásná, A. Nothnagel, and J. Böhm.Earth, Planets and Space, 77(1):40, Mar

    work page doi:10.1016/j.asr.2025.08.036 2025

  6. [6]

    doi: 10.1186/s40623-025-02159-z. S. Kiehlmann et al.ApJ, 961(2):240, Feb

    work page doi:10.1186/s40623-025-02159-z

  7. [7]

    doi: 10.3847/1538-4357/ad0c56. T. A. Koryukova, A. B. Pushkarev, A. V. Plavin, and Y. Y. Kovalev.MNRAS, 515(2):1736–1750, Sept

    work page doi:10.3847/1538-4357/ad0c56

  8. [8]

    doi: 10.1093/mnras/stac1898. Y. Y. Kovalev.ApJL, 707(1):L56–L59, Dec

    work page doi:10.1093/mnras/stac1898

  9. [9]

    doi: 10.1088/0004-637X/707/1/L56. Y. Y. Kovalev, L. Petrov, and A. V. Plavin.A&A, 598:L1,

    work page doi:10.1088/0004-637x/707/1/l56

  10. [10]

    doi: 10.1051/0004-6361/ 201630031. Y. Y. Kovalev et al.A&A, 700:L12, Aug

    work page doi:10.1051/0004-6361/

  11. [11]

    doi: 10.1051/0004-6361/202555400. B. Marcote et al.Nature, 577(7789):190–194, Jan

    work page doi:10.1051/0004-6361/202555400

  12. [12]

    J.McKeanetal

    doi: 10.1038/s41586-019-1866-z. J.McKeanetal. InAdvancing Astrophysics with the Square Kilometre Array (AASKA14),page84, Apr

    work page doi:10.1038/s41586-019-1866-z

  13. [13]

    doi: 10.22323/1.215.0084. A. Niell et al.Radio Science, 53(10):1269–1291,

    work page doi:10.22323/1.215.0084

  14. [14]

    doi: 10.1029/2018RS006617. R. P. Norris et al.PASA, 28(3):215–248, Aug

    work page doi:10.1029/2018rs006617

  15. [15]

    doi: 10.1071/AS11021. L. Petrov.AJ, 165(4):183, Apr

    work page doi:10.1071/as11021

  16. [16]

    doi: 10.3847/1538-3881/acc174. L. Petrov et al.MNRAS, 414:2528–2539, July

    work page doi:10.3847/1538-3881/acc174

  17. [17]

    doi: 10.1111/j.1365-2966.2011.18570.x. L. Petrov et al.MNRAS, 485(1):88–101, May

    work page doi:10.1111/j.1365-2966.2011.18570.x 2011

  18. [18]

    doi: 10.1093/mnras/stz242. L. Petrov, C. Ploetz, and M. Schartner.arXiv e-prints, art. arXiv:2506.15859, June

    work page doi:10.1093/mnras/stz242

  19. [19]

    doi: 10.48550/arXiv.2506.15859. L. Y. Petrov and Y. Y. Kovalev.ApJSS, 276(2):38, Feb

    work page doi:10.48550/arxiv.2506.15859

  20. [20]

    doi: 10.3847/1538-4365/ad8c36. B. G. Piner and P. G. Edwards.ApJ, 853(1):68, Jan

    work page doi:10.3847/1538-4365/ad8c36

  21. [21]

    doi: 10.3847/1538-4357/aaa425. A. V. Plavin, Y. Y. Kovalev, and L. Y. Petrov.ApJ,

    work page doi:10.3847/1538-4357/aaa425

  22. [22]

    doi: 10.3847/1538-4357/aaf650. A. V. Plavin, Y. Y. Kovalev, Y. A. Kovalev, and S. V. Troitsky.MNRAS, 523(2):1799–1808, Aug

    work page doi:10.3847/1538-4357/aaf650

  23. [23]

    doi: 10.1093/mnras/stad1467. M. J. Reid and M. Honma.ARA&A, 52:339–372,

    work page doi:10.1093/mnras/stad1467

  24. [24]

    doi: 10.1029/2023RS007734. T. Treu.ARA&A, 48:87–125, Sept

    work page doi:10.1029/2023rs007734

  25. [25]

    doi: 10.1146/annurev-astro-081309-130924. S. Weston et al.PASA, 40:e041, Sept

    work page doi:10.1146/annurev-astro-081309-130924

  26. [26]

    doi: 10.1017/pasa.2023.33. M. H. Xu and P. Charlot.AJ, 169(3):173, feb

    work page doi:10.1017/pasa.2023.33 2023

  27. [27]

    doi: 10.3847/1538-3881/adb133. M. H. Xu et al.Journal of Geodesy, 95(5):51, May

    work page doi:10.3847/1538-3881/adb133

  28. [28]

    doi: 10.1007/s00190-021-01496-7. M. H. Xu et al.JGR-SE, 128(3),

    work page doi:10.1007/s00190-021-01496-7

  29. [29]

    doi: 10.1029/2022JB02519810.1002/essoar.10512041.1. 7

    work page doi:10.1029/2022jb02519810.1002/essoar.10512041.1