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arxiv: 2606.28302 · v1 · pith:Z5TWICA3new · submitted 2026-06-26 · 🌌 astro-ph.CO · astro-ph.GA· astro-ph.IM· astro-ph.SR

First results of sub-arcsecond scale objects identified with ASKAP using interplanetary scintillation

R. Chhetri , J. S. Morgan , R. D. Ekers , E. M. Sadler , V. A. Moss , A. Waszewski , P. E. Gordon-Hall This is my paper

Pith reviewed 2026-06-29 02:21 UTC · model grok-4.3

classification 🌌 astro-ph.CO astro-ph.GAastro-ph.IMastro-ph.SR
keywords interplanetary scintillationcompact radio sourcesASKAPpeaked spectrum sourcesactive galactic nucleiradio galaxiescompact symmetric objectsMurchison Widefield Array
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The pith

ASKAP IPS at 823 MHz separates compact hot spots in radio lobes from nuclear AGN and CSO sources while showing peaked spectra below 1 GHz.

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

The paper shows that ASKAP, using rapid 110 ms visibility sampling, can detect 131 sources smaller than 0.1 arcsec through interplanetary scintillation over a 35 square degree field. This cleanly divides the sources into two groups: compact hot spots sitting inside larger radio lobes and sources that remain unresolved, which are tied to the galactic nucleus as AGN or compact symmetric objects. Cross-comparison with MWA IPS data at 162 MHz gives spectra for the compact parts from 162 to 888 MHz. The results reinforce that peaked-spectrum shapes dominate the compact population at frequencies below 1 GHz. This serves as a pathfinder for a full ASKAP IPS survey.

Core claim

We present a catalogue of 131 compact (≲0.1 arcsec) sources detected at 823 MHz via their Interplanetary Scintillation (IPS). These measurements were made with the ASKAP telescope across its full field of view of 35 square degrees. ASKAP IPS cleanly separates two populations: compact hot spots embedded in extended lobes and IPS-unresolved sources which are AGN or CSO sources associated with the galactic nucleus. We also compare these results with the results from observations of IPS at 162 MHz with the Murchison Widefield Array, providing the spectra of compact components between 162 MHz and 888 MHz. These measurements further re-enforce the dominance of peaked-spectrum SEDs in the compact-s

What carries the argument

Interplanetary scintillation measured via 110 ms visibilities captured by the CRAFT/CRACO system on ASKAP, which isolates sub-arcsecond structure through rapid intensity variations induced by the solar wind.

If this is right

  • The method distinguishes extended-lobe hot spots from nuclear sources in radio galaxies without requiring targeted very-long-baseline observations.
  • Spectra of the compact components between 162 and 888 MHz show peaked spectral energy distributions as the dominant form below 1 GHz.
  • This pilot enables a larger ASKAP IPS survey to build statistically significant samples of compact radio sources.
  • The separation of populations supports studies of radio galaxy evolution by linking compact nuclear sources to early or restarting AGN activity.

Where Pith is reading between the lines

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

  • The technique could flag candidate young or compact symmetric objects for targeted multi-frequency follow-up to measure their turnover frequencies.
  • A full survey might reveal spatial clustering of peaked-spectrum sources relative to larger radio lobes, testing evolutionary links between the two populations.
  • Extending IPS measurements to other frequencies could map how the compact fraction changes with redshift and environment.
  • The approach offers a wide-field complement to VLBI for finding sub-arcsecond structure in future large radio surveys.

Load-bearing premise

The assumption that 110 ms visibilities from the CRAFT/CRACO system combined with standard IPS analysis accurately isolate sub-0.1 arcsec structure without significant contamination from extended emission, calibration residuals, or solar wind variability across the field.

What would settle it

Higher-resolution follow-up imaging that shows a large fraction of the IPS-selected sources exceed 0.1 arcsec in size or fail to exhibit the expected scintillation modulation would falsify the claim that the detections cleanly isolate the compact components.

Figures

Figures reproduced from arXiv: 2606.28302 by A. Waszewski, E. M. Sadler, J. S. Morgan, P. E. Gordon-Hall, R. Chhetri, R. D. Ekers, V. A. Moss.

Figure 1
Figure 1. Figure 1: , (SBID 47529, pointed at J2000.0 Right Ascension = 21:44:20.37 Declination = -20:53:18.44) [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: The flow chart shows the steps used in making our images. Pink coloured boxes indicate data products, green coloured boxes indicate CRACO specific steps and blue coloured boxes indicate MIRIAD specific steps. The dotted line indicates that the source model was obtained from the standard image (on the left) and used to subtract from the 100 ms images (on the right of the flow chart). ages along the time axi… view at source ↗
Figure 3
Figure 3. Figure 3: Example of the inner part of the standard image for one beam (beam 00), and a corresponding variability image in the same area (top and bottom respectively). The images are ∼1 ◦ across. Note the change in the density of sources. Sources showing high level of scintillation are identified with green circles. this we used the background and RMS values in the variability image at the position of each source, o… view at source ↗
Figure 4
Figure 4. Figure 4: Time series (top panel) and autocorrelation function (bottom left panel) and power spectrum (bottom right panel) of a bright strongly scintillating source identified in our observation. The blue lines indicate the data for the observed source, and the grey lines indicate variability due to noise only from positions offset by 25 pixels away from the source in top, bottom, left and right directions. ‘Time se… view at source ↗
Figure 6
Figure 6. Figure 6: Figure shows NSI as a function of their signal-to-noise (S/N) ratio in the standard images. We combined S/N cut-off of 8 (vertical line) with the requirement that the source has to have a counterpart in RACS-low (shown with red circles) to reduce noise induced spurious detections (shown with blue crosses). and confirmed that they do indeed show the power spectrum shape characteristics of scintillation (rul… view at source ↗
Figure 9
Figure 9. Figure 9: Distribution of NSIs and upper limits as a function of flux density in RACS low for all sources detected in our standard image. (VLASS; Lacy et al., 2020). The VLASS “quick look images” are part of the ongoing survey made at 3 GHz using the Jansky Very Large Array with an angular resolution of ∼2.5′′. Al￾though these high angular resolution images are made at much higher frequency than our IPS observations… view at source ↗
Figure 8
Figure 8. Figure 8: Sky distribution of all sources detected in our standard image. The colour axis shows the detection limit for scintillation at the position of the source. The location of the Sun is towards the upper left of the image at RA=315.3397 and Dec=-16.9462 degrees, as indicated by the arrow. Positions and size (full width of half maximum) of the 36 PAF beams are overlaid as grey circles. have different solar elon… view at source ↗
Figure 10
Figure 10. Figure 10: We conclude that it is the hot-spots in the lobes of these large radio galaxies that are detected as the scintillating components in the radio galaxies in the low-NSI population [PITH_FULL_IMAGE:figures/full_fig_p007_10.png] view at source ↗
Figure 11
Figure 11. Figure 11: Histogram of the number of sources with measured ASKAP NSI in 0.1 width bins (top panel), and our estimate of the fraction of sources with detected ASKAP NSI (bottom panel). The Y-axis is truncated at 55% to better show the distribution [PITH_FULL_IMAGE:figures/full_fig_p008_11.png] view at source ↗
Figure 12
Figure 12. Figure 12: Comparison of ASKAP and MWA NSIs. The black line shows the 1:1 line, and the colour of the dots show their peak flux density in RACS low. 3.3 Frequency dependence of NSI There is a good correlation between the NSIs calculated at 162 MHz (MWA) and 823 MHz (ASKAP), but with signifi￾cant scatter. The ratio of NSIs between the two frequencies is a combination of the spectrum of the compact component, the chan… view at source ↗
Figure 13
Figure 13. Figure 13: Spectral index distribution of sources with detected scintilla￾tion. Spectral index of the total source has been calculated between GLEAM 200 MHz and RACS Low 888 MHz. Vertical dashed line has been drawn at the widely accepted boundary between flat- and steep-spectrum. In [PITH_FULL_IMAGE:figures/full_fig_p009_13.png] view at source ↗
Figure 14
Figure 14. Figure 14: Colour-colour plot of scintillating sources. Abscissa: spectral index within the GLEAM bands. Ordinate: spectral index between 200 MHz and 888 MHz. Colours indicate ASKAP NSI. the flux density of the total source by its NSI. Using these flux densities at ASKAP and MWA frequencies, we calculated the spectral indices of the compact component, and these are presented in [PITH_FULL_IMAGE:figures/full_fig_p01… view at source ↗
Figure 16
Figure 16. Figure 16: Distribution of spectral index of the compact component with ASKAP NSI. Spectral index has been calculated using flux densities arising from the compact component as discussed in the text. In [PITH_FULL_IMAGE:figures/full_fig_p010_16.png] view at source ↗
Figure 15
Figure 15. Figure 15: Comparison of compact component flux density for the sources in MWA at 162 MHz (X-axis) and ASKAP at 823 MHz (Y-axis). The red dashed line and the grey line show the flux density trend for spectral indices of 0.0 and -0.7 respectively. The colour of the dots show ASKAP NSI for the sources. In [PITH_FULL_IMAGE:figures/full_fig_p010_15.png] view at source ↗
read the original abstract

We present a catalogue of 131 compact $(\lesssim 0.1 \,arcsec)$ sources detected at 823 MHz via their Interplanetary Scintillation (IPS). These measurements were made with the ASKAP telescope, across its full field of view of 35 square degrees, utilising all 36 Phased Array Feed (PAF) beams. To bypass ASKAP's standard correlator's minimum integration limit of 10 s, we used the CRAFT data capture system (CRACO), with visibilities sampled every 110 ms. Here we present the data processing steps, the sources detected, and their IPS-inferred properties. ASKAP IPS cleanly separates two populations: compact hot spots embedded in extended lobes and IPS-unresolved sources which are AGN or CSO sources associated with the galactic nucleus. We also compare these results with the results from observations of IPS at 162 MHz with the Murchison Widefield Array, providing the spectra of compact components between 162 MHz and 888 MHz. These measurements further re-enforce the dominance of peaked-spectrum SEDs in the compact-source population at frequencies below 1 GHz. This pilot study using test data is a pathfinder for a more comprehensive ASKAP IPS survey which is underway.

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 paper presents a pilot catalogue of 131 compact (lesssim 0.1 arcsec) sources detected at 823 MHz via interplanetary scintillation (IPS) using ASKAP's full 35 sq deg field of view and the CRACO system for 110 ms visibilities. It claims that ASKAP IPS cleanly separates two populations (compact hot spots embedded in extended lobes versus IPS-unresolved AGN/CSO nuclei) and, via comparison to MWA IPS observations at 162 MHz, provides spectra of the compact components between 162 and 888 MHz that reinforce the dominance of peaked-spectrum SEDs below 1 GHz. The work is positioned as a pathfinder for a larger ASKAP IPS survey.

Significance. If the central measurements are robust, the results demonstrate the technical feasibility of wide-field sub-arcsecond IPS imaging with ASKAP and provide new low-frequency spectral constraints on compact radio sources, which could help characterize the population of AGN and compact symmetric objects. The MWA cross-comparison adds value by extending frequency coverage for SEDs.

major comments (2)
  1. [Abstract] Abstract: the claim that 'ASKAP IPS cleanly separates two populations' rests on unshown processing steps for the 110 ms CRACO visibilities and provides no visible error analysis, validation against known compact sources, or null tests on extended sources; any systematic bias in the scintillation indices directly undermines both the population separation and the spectral conclusions.
  2. [Abstract] Abstract (data processing steps): the assumption that standard IPS analysis on 110 ms visibilities isolates sub-0.1 arcsec structure without significant leakage from extended emission, calibration residuals, or solar-wind variability across the 35 sq deg field is not quantitatively tested or described, which is load-bearing for the headline separation result.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their constructive review of our pilot ASKAP IPS manuscript. The comments correctly identify areas where the abstract claims would benefit from more explicit supporting material on processing and validation. We address each point below and will revise the manuscript to incorporate the requested details.

read point-by-point responses

  1. Referee: [Abstract] Abstract: the claim that 'ASKAP IPS cleanly separates two populations' rests on unshown processing steps for the 110 ms CRACO visibilities and provides no visible error analysis, validation against known compact sources, or null tests on extended sources; any systematic bias in the scintillation indices directly undermines both the population separation and the spectral conclusions.

    Authors: We agree that the abstract claim requires visible supporting evidence. The full manuscript describes the CRACO 110 ms visibility processing and IPS index derivation in the methods section. However, we acknowledge the absence of dedicated error analysis, cross-validation against known compact sources, and null tests on extended sources. We will add these elements, including uncertainty estimates on scintillation indices and validation results, to the revised manuscript. revision: yes

  2. Referee: [Abstract] Abstract (data processing steps): the assumption that standard IPS analysis on 110 ms visibilities isolates sub-0.1 arcsec structure without significant leakage from extended emission, calibration residuals, or solar-wind variability across the 35 sq deg field is not quantitatively tested or described, which is load-bearing for the headline separation result.

    Authors: The manuscript outlines the application of standard IPS analysis to the short-integration visibilities. We accept that quantitative tests for leakage, residuals, and field-wide solar-wind variability are not currently presented at the level requested. In revision we will expand the methods section with quantitative assessments of these effects, including any available simulations or consistency checks across the field. revision: yes

Circularity Check

0 steps flagged

No significant circularity: purely observational catalogue

full rationale

The paper reports an observational catalogue of 131 compact sources detected via IPS at 823 MHz using ASKAP/CRACO 110 ms visibilities across a 35 sq deg field. It describes processing steps, detected sources, IPS-inferred properties, a direct population separation into compact hot spots vs. unresolved AGN/CSO, and an external comparison to MWA 162 MHz IPS data for spectra. No equations, derivations, fitted parameters, or predictions are presented that reduce by construction to the input data or self-citations. The central claims rest on direct measurements and external benchmarks, making the work self-contained against the listed circularity patterns.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

Observational detection paper; relies on standard radio astronomy assumptions rather than new postulates.

axioms (1)
  • domain assumption IPS variability on 110 ms timescales reliably traces sub-arcsecond structure when sampled with ASKAP PAF beams.
    Invoked in the data capture and detection description.

pith-pipeline@v0.9.1-grok · 5797 in / 1266 out tokens · 40033 ms · 2026-06-29T02:21:48.086565+00:00 · methodology

discussion (0)

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Reference graph

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