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arxiv: 2606.26365 · v1 · pith:L7KKZS4Jnew · submitted 2026-06-24 · 🌌 astro-ph.IM

Extending the SKA Across Africa: The Case for a Continental African VLBI Network

Emmanuel K. Bempong-Manful , Jompoj Wongphechauxsorn , Jack Radcliffe , Melvin Hoare , Olga Bayandina , Pfesesani V. van Zyl , Cristina Garc\'ia-Mir\'o , Candela Chico
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Naomi Asabre Frimpong Hans-Rainer Kl\"ockner Valente Cuambe Carla S. Mitchell Saul P. Phiri Benedicta Woode Emmanuel Proven-Adzri Willice Obonyo Tyler L. Bourke Cristiana Spingola Matthias Kadler Ailing Wang Roger P. Deane Isabella Prandoni Rocco Lico James O. Chibueze Robert Beswick Simon Garrington Benito Marcote Tao An Marcello Giroletti Isaac M. Mutie Anne-Kathrin Baczko Johannes Allotey Stefano Giarratana Rasha M. Samir
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Pith reviewed 2026-06-26 00:47 UTC · model grok-4.3

classification 🌌 astro-ph.IM
keywords African VLBI NetworkSKA-MidVLBI baselinesradio astronomy infrastructureglobal VLBI coverageangular resolutionhuman capital development
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The pith

A continental African VLBI network with 9000 km baselines will exceed ngVLA resolution by about 10 percent at comparable frequencies while filling missing north-south coverage in global arrays.

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

The paper proposes a vision for an African VLBI Network that operates in tandem with SKA-Mid by placing radio telescopes at strategic sites across the continent. These sites would supply the long north-south and intermediate baselines that current global VLBI arrays lack, thereby raising both angular resolution and image quality for observations at all cosmic scales. With a longest baseline stretching roughly 9000 km between Rabat and Cassis, the network is projected to deliver modestly finer resolution than the ngVLA at similar frequencies. In addition to the technical gains, the paper argues that building and running the array would develop engineering and scientific expertise on the continent and stimulate related industries. The authors outline existing operational stations, ongoing refurbishment efforts, and a roadmap that includes limited deployment of SKA-Mid-type dishes.

Core claim

The central claim is that an African VLBI Network formed by refurbishing existing antennas and adding a modest number of SKA-Mid-type telescopes will create an "African arm" of SKA-VLBI whose maximum baseline reaches approximately 9000 km and thereby surpasses the resolution of the ngVLA by roughly 10 percent at similar frequencies while markedly improving global VLBI coverage and imaging fidelity.

What carries the argument

The continental African VLBI Network (AVN), formed by strategic north-south and intermediate baselines across refurbished and new SKA-Mid-type telescopes that close coverage gaps in the existing global VLBI array.

If this is right

  • The network will deliver higher angular resolution and better imaging fidelity than current global VLBI configurations for the same observing frequencies.
  • Global VLBI coverage will improve through the addition of the missing north-south and intermediate baselines.
  • The array will operate in close synergy with SKA-Mid, enabling transformational science across all cosmic scales.
  • Development and operation of the network will train engineers, data scientists, and astronomers while stimulating local industry.

Where Pith is reading between the lines

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

  • If the network reaches full operation, it could become the primary southern-hemisphere anchor for future space-VLBI or multi-messenger campaigns that require long baselines.
  • The same continental distribution that improves north-south coverage might also reduce scheduling conflicts for time-critical transient events observed jointly with northern arrays.
  • Sustained operation would require new data-transport and correlation infrastructure whose design could be reused by other large-scale scientific facilities on the continent.

Load-bearing premise

Partner countries will succeed in refurbishing or converting existing antennas and in deploying the additional SKA-Mid-type telescopes needed to reach the proposed 9000 km baselines.

What would settle it

A concrete observation that would settle the claim is whether at least three to five additional operational stations (including one near Rabat and one near Cassis) are brought online within the next decade and achieve the stated 9000 km baseline length at the target frequencies.

Figures

Figures reproduced from arXiv: 2606.26365 by Ailing Wang, Anne-Kathrin Baczko, Benedicta Woode, Benito Marcote, Candela Chico, Carla S. Mitchell, Cristiana Spingola, Cristina Garc\'ia-Mir\'o, Emmanuel K. Bempong-Manful, Emmanuel Proven-Adzri, Hans-Rainer Kl\"ockner, Isaac M. Mutie, Isabella Prandoni, Jack Radcliffe, James O. Chibueze, Johannes Allotey, Jompoj Wongphechauxsorn, Marcello Giroletti, Matthias Kadler, Melvin Hoare, Naomi Asabre Frimpong, Olga Bayandina, Pfesesani V. van Zyl, Rasha M. Samir, Robert Beswick, Rocco Lico, Roger P. Deane, Saul P. Phiri, Simon Garrington, Stefano Giarratana, Tao An, Tyler L. Bourke, Valente Cuambe, Willice Obonyo.

Figure 1
Figure 1. Figure 1: Overview of the locations of the decommissioned satellite antennas previously identified for inclusion in the SKA Partner countries array, together with the potential sites for new SKA-Mid–type antennas across Africa and other planned and current operational antennas. These locations illustrate a possible configuration of a future continental African VLBI array, with maximum baseline length between, e.g. M… view at source ↗
Figure 2
Figure 2. Figure 2: Frequency coverage of current African radio telescopes and SKA-Mid below 18 GHz compared with standard VLBI observing frequencies provided by EVNplanobs. The VLBI bands are shown as 256- MHz–wide boxes for reference. The boxes indicate possible frequency ranges for each telescope. The plot highlights existing overlaps as well as the expanded coverage achievable with future SKA-Mid–compatible receivers depl… view at source ↗
Figure 3
Figure 3. Figure 3: Top (left): uv-coverage comparison between SKA-Mid and AVN-remote stations. Top (right): uv-coverage comparison between current stations (blue), prospective stations (green), and future stations (red). Bottom: Results from simulation of a double point source at 12 GHz with 1.5 mas angular separation; Left panel – simulation results from current stations; Middle panel – simulation results from prospective s… view at source ↗
Figure 4
Figure 4. Figure 4: First row: Toy model of a relativistic jet to simulate a real scientific case with a value for declination of −30◦ and an observing time of 6 hours. Second row: uv-coverage comparison between the Current, Prospective and Future stations scenarios described in the text. Third row: Simulations of the jet with each array operating at SKA band-5a (6.5 GHz), each labelled correspondingly in the graph’s title. T… view at source ↗
read the original abstract

The African continent holds the key to unlocking the full potential of global Very Long Baseline Interferometry (VLBI). Strategic placement of radio telescopes across Africa provides the crucial north-south and intermediate baselines that are currently missing from the global VLBI network. This expansion will dramatically enhance imaging fidelity and resolution. In this chapter, we propose a vision for a continental African VLBI Network (AVN) that will operate in close synergy with SKA-Mid, enabling transformational science across all cosmic scales. While only the Hartebeesthoek Radio Astronomy Observatory (HartRAO) in South Africa and the Ghana Radio Astronomy Observatory (GRAO) are currently operational, several partner countries are in the process of refurbishing or converting existing antennas. Here, we advocate for the expansion of this network through the deployment of a limited number of SKA-Mid-type telescopes across the continent, creating an "African arm" of SKA-VLBI. With a maximum baseline of ~ 9000 km (from Rabat, Morocco to Cassis, Mauritius), the proposed continental facility will surpass for example, the resolution that will be achieved by the next generation Very Large Array (ngVLA) by ~ 10 % at similar observing frequencies and significantly enhance global VLBI coverage. Beyond the scientific and technical gains, the AVN represents a unique opportunity for sustainable growth in human capital, education, and innovation across Africa. Developing and operating a continental VLBI array will train the next generation of engineers, data scientists, and astronomers, stimulate local industry, and inspire public engagement in science and technology. We outline the current status, challenges, and potential roadmap towards realizing this vision, and we highlight how a continental African VLBI network will position Africa at the forefront of global radio astronomy.

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 / 1 minor

Summary. The manuscript is a vision paper advocating for a Continental African VLBI Network (AVN) operating in synergy with SKA-Mid. It argues that strategic deployment of telescopes across Africa will supply missing north-south and intermediate baselines to the global VLBI array, dramatically improving imaging fidelity and resolution. The paper notes current operational sites (HartRAO, GRAO), ongoing refurbishments in partner countries, and proposes limited new SKA-Mid-type antennas. A central quantitative claim is that a maximum baseline of ~9000 km (Rabat to Cassis) will exceed ngVLA resolution by ~10% at comparable frequencies, while also delivering human-capital and socio-economic benefits across Africa. The document outlines status, challenges, and a high-level roadmap.

Significance. If realized, the proposed AVN would address documented gaps in global VLBI uv-coverage, potentially enabling higher-resolution imaging across cosmic scales and strengthening SKA-VLBI capabilities. The capacity-building aspects are a notable strength for a developing region. As a forward-looking advocacy piece without new derivations, simulations, or empirical data, its significance is prospective rather than immediate; the technical case rests on standard interferometric principles but requires quantitative support for the specific performance claims.

major comments (1)
  1. [Abstract] Abstract: The claim that a ~9000 km baseline 'will surpass ... the resolution that will be achieved by the next generation Very Large Array (ngVLA) by ~10 % at similar observing frequencies' is presented without supporting calculations, uv-coverage simulations, or frequency-specific comparisons. This quantitative assertion is load-bearing for the paper's central technical argument and must be substantiated (or qualified) for the manuscript to be credible.
minor comments (1)
  1. [Abstract] Abstract: The phrasing 'surpass for example, the resolution' is grammatically awkward and should be revised for clarity.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the constructive comment on the need to support the resolution claim. We address the point below and will revise the manuscript to ensure the technical argument is properly substantiated.

read point-by-point responses

  1. Referee: [Abstract] Abstract: The claim that a ~9000 km baseline 'will surpass ... the resolution that will be achieved by the next generation Very Large Array (ngVLA) by ~ 10 % at similar observing frequencies' is presented without supporting calculations, uv-coverage simulations, or frequency-specific comparisons. This quantitative assertion is load-bearing for the paper's central technical argument and must be substantiated (or qualified) for the manuscript to be credible.

    Authors: We agree that the claim as stated requires substantiation or qualification. The ~10% improvement is based on the standard interferometric resolution formula θ ≈ λ / B_max at comparable frequencies, with the proposed 9000 km baseline exceeding the ngVLA maximum baseline by that margin; however, this derivation is not shown in the current text. In the revised manuscript we will either insert a short explanatory clause in the abstract and a supporting sentence in the main text (e.g., near the discussion of baseline lengths) or qualify the statement as an estimate derived from maximum baseline lengths. Detailed uv-coverage simulations lie beyond the scope of this vision paper, but the simple resolution comparison can be made explicit without new modeling. revision: yes

Circularity Check

0 steps flagged

No significant circularity; vision paper with no derivations

full rationale

This document is a forward-looking advocacy and vision paper outlining a proposed continental African VLBI network. It advances no mathematical derivations, fitted parameters, equations, simulations, or empirical predictions that could reduce to their own inputs. The central claim of ~9000 km baselines yielding ~10% better resolution than ngVLA is asserted without calculation, uv-coverage analysis, or self-referential logic in the text. Deployment assumptions are presented as policy preconditions, not load-bearing premises of a proof. No self-citations, ansatzes, or uniqueness theorems are invoked in a manner that creates circularity. The paper is self-contained as a proposal.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

No mathematical models, data analysis, or new physical postulates; the text relies on established VLBI principles without introducing free parameters, axioms beyond standard domain knowledge, or invented entities.

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Reference graph

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