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arxiv: 2606.26940 · v1 · pith:RESYWTKPnew · submitted 2026-06-25 · 🌌 astro-ph.IM

VLBI with SKAMPI, the SKA-Mid MPIfR dish demonstrator

Jompoj Wongphechauxsorn , Niclas Alexander Esser , Tobias Winchen , Jan Wagner , Uwe Bach , Hans-Rainer Kl\"ockner , Michael Kramer , Gundolf Wieching
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Ewan Barr Jonathan Quick Roger Deane Cormac Reynolds Phil Edwards Chris Phillips Matthias Kadler Roopesh Ojha
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Pith reviewed 2026-06-26 03:08 UTC · model grok-4.3

classification 🌌 astro-ph.IM
keywords VLBISKAMPIfringe detectionSKA prototyperadio interferometryS-bandEVNLBA
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The pith

SKAMPI detects VLBI fringes in S-band with the EVN, LBA, and VLBA.

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 SKAMPI prototype can operate in VLBI mode by reporting successful fringe detections during its first experiments. It evaluates signal integration over time and image formation quality when the dish links to networks spanning Europe, Australia, and North America. A sympathetic reader would care because this shows an SKA precursor can contribute to high-resolution observations that demand widely separated telescopes. The results indicate that the hardware and observing setup function without fundamental barriers in the tested configuration.

Core claim

The authors present the first fringe-finding experiments with SKAMPI in S-band, including successful fringe detections and an evaluation of integration and imaging performances when the telescope participates in observations with the European VLBI Network, the Long Baseline Array, and the Very Long Baseline Array.

What carries the argument

The SKAMPI telescope in VLBI mode, which records and correlates signals across intercontinental baselines to produce detectable fringes.

If this is right

  • SKAMPI can participate in routine VLBI campaigns that require extended signal integration.
  • The achieved imaging performance supports use in global arrays for source structure studies.
  • The S-band results provide a baseline for testing the dish at additional frequency bands.
  • Prototype dishes of this class can be added to existing VLBI networks with current correlation systems.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Successful operation at the SKA site suggests the full SKA-Mid array could supply dense southern baselines for VLBI.
  • Calibration techniques validated here may reduce setup time for future SKA VLBI sessions.
  • Extension to higher frequencies would test whether the same integration performance scales with wavelength.

Load-bearing premise

The reported fringe detections represent genuine signals from astronomical sources rather than noise or calibration artifacts.

What would settle it

Re-reduction of the visibility data with independent software showing no fringes above the expected noise level for the integration times used.

Figures

Figures reproduced from arXiv: 2606.26940 by Chris Phillips, Cormac Reynolds, Ewan Barr, Gundolf Wieching, Hans-Rainer Kl\"ockner, Jan Wagner, Jompoj Wongphechauxsorn, Jonathan Quick, Matthias Kadler, Michael Kramer, Niclas Alexander Esser, Phil Edwards, Roger Deane, Roopesh Ojha, Tobias Winchen, Uwe Bach.

Figure 1
Figure 1. Figure 1: Overview of SKA-MPI Software Architecture: Shown are the individual components of the system, the color coding indicates the type and arrows indicates the communication between the objects. will be executed is specified in the observing queue by the user, respectively also the observation mode. The ProcessBot is based on the celery2 distributed task queue system, ensuring that multiple workers can process … view at source ↗
Figure 2
Figure 2. Figure 2: (Left) Simulated visibility amplitude from EVN and EVN with SKAMPI. The object used in this simulation is a double point source with 1 Jy flux density at 0.1 mas separation in the N-S direction from each other. This demonstrates that the source can be distinguished from a point source even at an angular separation corresponding to 20% of the nominal resolution. (0.4 mas) with more than 20% amplitude differ… view at source ↗
Figure 3
Figure 3. Figure 3: The (𝑢, 𝑣) coverage from simulated 24 hours observation at 2 GHz for an EVN observation with and without SKAMPI. The simulated source is located at 𝛿 = -10◦ . Left: SKAMPI will double the number of rare data points in the outermost part of the (𝑢, 𝑣) domain and even provide the longest baselines (red). Right: SKAMPI-Hart (red) baselines will even the same parts of the 𝑢𝑣 plane in a similar manner as inner-… view at source ↗
Figure 4
Figure 4. Figure 4: The (𝑢, 𝑣) coverage from simulated 24 hours observation at 2 GHz for an LBA observation with and without SKAMPI. The simulated source is located at 𝛿 = 10◦ . Left: Showing that SKAMPI will double the number of rare data points in the outermost part of the (𝑢, 𝑣) domain and provide the second-longest baselines. Right: SKAMPI-Hart baselines willwill even the same parts of the 𝑢𝑣 plane in a similar manner as … view at source ↗
Figure 5
Figure 5. Figure 5: Distribution of baseline lengths for EVN with and without SKAMPI. This histogram shows the frequency of different baseline lengths (in km) formed between SKAMPI and other EVN stations, highlighting the range of angular resolutions achieved. The SKAMPI-HartRAO baseline (814.0 km) is similar to the Ef￾Mc baseline (757.0 km), providing redundancy for amplitude calibration. There are a total of 45 unique non-z… view at source ↗
Figure 6
Figure 6. Figure 6: Distribution of baseline lengths for SKAMPI with the LBA. This histogram illustrates the frequency of different baseline lengths (in km) formed between SKAMPI and other LBA stations, showcasing the extent of angular resolutions achieved. The SKAMPI-Hh baseline (814.0 km) is similar to the Td-Ho baseline (831.8 km), providing important redundancy. There are a total of 55 unique non-zero baselines among the … view at source ↗
Figure 8
Figure 8. Figure 8: LBA observations baseline (SKAMPI − Parkes) phase and amplitude versus channels plot (upper and lower) for IF1 (RCP), IF2 (RCP), IF1 (LCP), and IF2 (LCP) from left to right, respectively, at 2 GHz on the 2024 May 24 TANAMI observation. The results indicate successful fringe finding: for both IFs, the phase varies linearly across the bands, while the amplitude shows a smooth profile across the channel [PIT… view at source ↗
Figure 9
Figure 9. Figure 9: Frequency coverage of SKAMPI to SKA and Effelsberg (Eff; represents the EVN) and ATCA (represents the LBA frequency capability) showing missing frequency coverages between SKAMPI and these instruments. The frequency coverage of the SKA-Mid precursor, MeerKAT, also shown. 11 [PITH_FULL_IMAGE:figures/full_fig_p011_9.png] view at source ↗
read the original abstract

The SKA-MPIfR telescope (SKAMPI) is a prototype SKA-Mid antenna located at the SKA site in the Karoo Desert, South Africa. It is funded by the Max Planck Society, through the Max Planck Institute for Radio Astronomy (MPIfR), and operated in collaboration with the South African Radio Astronomy Observatory (SARAO). The first fringe-finding experiments have been conducted with the European VLBI Network and the southern hemisphere Long Baseline Array, connecting SKAMPI with Europe and Australia. Here we present early SKAMPI VLBI mode results in S-Band, including successful fringe detections and evaluating the integration and imaging performances of SKAMPI in observations with the EVN, LBA, and VLBA.

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

1 major / 0 minor

Summary. The manuscript introduces the SKA-MPIfR telescope (SKAMPI) as a prototype SKA-Mid antenna and reports the first S-band fringe-finding experiments conducted with the EVN, LBA, and VLBA. It claims successful fringe detections and evaluates the integration and imaging performances of SKAMPI in these VLBI observations.

Significance. Demonstrating VLBI functionality with an SKA-Mid prototype would be significant for validating antenna performance and enabling future SKA participation in global VLBI networks, provided the detections are quantitatively substantiated.

major comments (1)
  1. Abstract: the central claim of 'successful fringe detections' is load-bearing for all downstream statements on integration time and imaging performance, yet no quantitative metrics (peak SNR, phase closure, delay-rate solutions, or comparison to expected thermal noise) are provided to distinguish genuine VLBI signals from noise or calibration artifacts.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the detailed review and the emphasis on quantitative substantiation of the fringe detections. We address the single major comment below and will incorporate the requested metrics into a revised manuscript.

read point-by-point responses

  1. Referee: [—] Abstract: the central claim of 'successful fringe detections' is load-bearing for all downstream statements on integration time and imaging performance, yet no quantitative metrics (peak SNR, phase closure, delay-rate solutions, or comparison to expected thermal noise) are provided to distinguish genuine VLBI signals from noise or calibration artifacts.

    Authors: We agree that explicit quantitative metrics are required to support the central claim of successful fringe detections. The revised manuscript will include measured peak SNR values for the detected fringes, verification of phase closure on the triangles involving SKAMPI, the derived delay-rate solutions, and direct comparisons of the observed SNR against the expected thermal noise based on system equivalent flux density, integration time, and bandwidth. These additions will be placed in the results section and referenced from the abstract to underpin the statements on integration performance and imaging. revision: yes

Circularity Check

0 steps flagged

No circularity: purely observational report with no derivations or fitted predictions

full rationale

The paper reports observational results from VLBI fringe detections with SKAMPI in S-band using EVN, LBA, and VLBA, including integration and imaging performance evaluations. No equations, derivations, parameter fits, predictions, or ansatzes are present in the abstract or described structure. The central claims rest on empirical detections rather than any mathematical chain that could reduce to self-definition or self-citation. No load-bearing steps match the enumerated circularity patterns; the work is self-contained as a technical report of telescope performance.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

No mathematical model, free parameters, axioms, or invented entities appear in the abstract; content is an observational technical report.

pith-pipeline@v0.9.1-grok · 5721 in / 922 out tokens · 74169 ms · 2026-06-26T03:08:43.280428+00:00 · methodology

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