Unravelling the nonthermal emissions from the quiet solar corona with the SKA

Devojyoti Kansabanik; Divya Oberoi; Eduard Kontar; Peijin Zhang; Rohit Sharma; Surajit Mondal; Xingyao Chen

arxiv: 2607.00682 · v1 · pith:GPL7KCEInew · submitted 2026-07-01 · 🌌 astro-ph.SR

Unravelling the nonthermal emissions from the quiet solar corona with the SKA

Surajit Mondal , Divya Oberoi , Rohit Sharma , Peijin Zhang , Devojyoti Kansabanik , Xingyao Chen , Eduard Kontar This is my paper

Pith reviewed 2026-07-02 05:55 UTC · model grok-4.3

classification 🌌 astro-ph.SR

keywords quiet solar coronanonthermal emissionsradio observationsSKAcoronal heatingparticle accelerationmagnetic reconnectionradio transients

0 comments

The pith

The SKA will detect weak nonthermal radio emissions from the quiet solar corona and associate them with thermal structures.

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

Past studies of nonthermal emissions in the quiet solar corona have been hampered by weak signals and insufficient image quality in radio observations. The paper claims the SKA's high sensitivity and fine spectroscopic snapshot imaging will overcome these limits to detect the emissions in total intensity and polarization. High angular resolution will then link the radio sources one-to-one with thermal counterparts, allowing direct measurement of energy partition in weak events and new tests of acceleration and reconnection models. This same data may also trace how energy moves from the photosphere into the corona.

Core claim

The SKA, with its excellent sensitivity as well as its exquisite spectroscopic snapshot PSF would be a game-changer in this field. It would not only allow us to detect and characterise these emissions in Stokes I, but would also allow us to investigate their polarisation properties as well. The high angular resolution offered by the SKA will allow a unique association of the detected radio transients with their thermal counterparts. This would enable us to investigate the thermal-nonthermal energy partition even for these rather weak transient emissions, which in turn would allow validation of particle acceleration and magnetic reconnection theories in a regime vastly different from that don

What carries the argument

SKA sensitivity together with its spectroscopic snapshot PSF and high angular resolution for source association.

If this is right

Detection and characterization of the emissions in Stokes I.
Investigation of their polarization properties.
Unique association of radio transients with thermal counterparts via high resolution.
Measurement of thermal-nonthermal energy partition for weak events.
Validation of particle acceleration and reconnection theories plus a new probe of coronal heating.

Where Pith is reading between the lines

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

If detections occur, the same SKA capabilities could be used on other stars to study coronal energy budgets.
Non-detections would place quantitative upper limits on the occurrence rate or brightness of such transients.
Combined SKA plus EUV or X-ray data sets could test whether the radio transients account for a measurable fraction of the required heating flux.

Load-bearing premise

Nonthermal emissions exist at flux levels and spatial-spectral structures that the SKA can detect and separate from confusion or artifacts.

What would settle it

SKA images of the quiet solar corona showing no separable nonthermal radio transients above the projected sensitivity or with no clear one-to-one thermal matches.

Figures

Figures reproduced from arXiv: 2607.00682 by Devojyoti Kansabanik, Divya Oberoi, Eduard Kontar, Peijin Zhang, Rohit Sharma, Surajit Mondal, Xingyao Chen.

**Figure 1.** Figure 1: The left panel shows the Stokes I radio contours overlaid on top of an EUV image. The blue, white, magenta and cyan contours correspond to images made at 1.057, 1.313, 1.441, and 1.685 GHz respectively. The right panel shows the Stokes I radio spectrum as well as the variation of the degree of circular polarisation with frequency. The black dashed lines indicates the expected circular polarisation fraction… view at source ↗

**Figure 2.** Figure 2: It shows the fraction of observation time for which these transients were detected at any given location of the solar disc. The contours represent the corresponding Stokes I image, and correspond to 0.2, 0.4, 0.6, 0.8, 0.9, and 0.95 times the peak. The figure is adapted from Mondal et al. (2023b). the GHz frequencies and the SKA Low, which operates at the metre-wave bands. Considering the different instrum… view at source ↗

**Figure 3.** Figure 3: The spectrum and the flux density times series at the spatial location of one example transient are shown in panels (a) and (b), respectively. The magenta and blue points of the spectrum have a resolution of 160 kHz and 40 kHz respectively. Inset in panel (a) shows the zoomed in version of the frequency range indicated by the gray box. These panels clearly demonstrate both the narrowband and impulsive natu… view at source ↗

read the original abstract

Investigation of the nonthermal emissions from the quiet solar corona has been rather limited. This primarily stems from the fact that the emission is expected to be quite weak and very high dynamic range images are required to detect such emissions. Although, the few detections of the nonthermal emissions have all come from the radio band, the past observations had several issues, the most important being the low image fidelity and lack of simultaneous broadband observation capability. Recent observations have been able to tackle many of these prior difficulties using modern instrumentation, and have produced multiple interesting results. In spite of these improvements, multiple challenges remain. For example, most of the recent investigations were only able to focus on the brightest of these events, due to rather poor spectroscopic snapshot PSF of the instruments. The SKA, with its excellent sensitivity as well as its exquisite spectroscopic snapshot PSF would be a game-changer in this field. It would not only allow us to detect and characterise these emissions in Stokes I, but would also allow us to investigate their polarisation properties as well. The high angular resolution offered by the SKA will allow a unique association of the detected radio transients with their thermal counterparts. This would enable us to investigate the thermal-nonthermal energy partition even for these rather weak transient emissions, which in turn would allow validation of particle acceleration and magnetic reconnection theories in a regime vastly different from that done previously. In addition, characterization of the nonthermal emissions of these weak coronal transients may also provide a new probe to understand how energy is transferred from the photosphere and dumped into the corona, and thus serve as a new tool to tackle the coronal heating problem.

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.

Desk Editor's Note private letter to a colleague

This is a perspective piece on SKA's potential for quiet-corona nonthermal radio work that restates known challenges without adding quantitative projections or new analysis.

read the letter

The core takeaway is that this paper lays out why weak nonthermal emissions from the quiet solar corona have been difficult to observe and claims SKA will change that through better sensitivity, snapshot PSF, and polarization capability. It connects the dots to reconnection tests and coronal heating but stays at the level of a science case summary.

It does a decent job recapping the historical limits: low image fidelity, lack of simultaneous broadband data, and how even recent instruments struggle with the weakest events due to PSF issues. The authors clearly know the radio solar literature and the specific observational bottlenecks.

The soft spots are in the projections themselves. The claims that SKA will detect these emissions, measure their polarization, and allow unambiguous thermal-nonthermal associations rest on qualitative statements about instrument specs. There are no flux estimates, brightness temperature ranges, source size assumptions, or snapshot imaging simulations to show the performance margin actually exists in the quiet corona regime. That matches the stress-test note exactly.

This paper is for solar radio astronomers who need a concise overview of the science case for SKA in this area. A reader already working on quiet corona transients might find the summary useful for framing proposals, but it won't supply new methods or results. I would not cite it.

It shows honest engagement with the literature and clear thinking about the goals. I would send it for peer review at a journal that takes instrument science cases or perspectives, with the expectation that referees will ask for more concrete numbers on detectability.

Referee Report

1 major / 0 minor

Summary. The manuscript reviews limitations in prior radio observations of weak nonthermal emissions from the quiet solar corona, notes recent instrumental improvements, and projects that the SKA's sensitivity, spectroscopic snapshot PSF, and angular resolution will enable detection and characterization of these emissions in Stokes I and polarization, unambiguous association with thermal counterparts, measurement of thermal-nonthermal energy partition, validation of particle acceleration and reconnection models in a new regime, and a new probe of coronal heating mechanisms.

Significance. If the projected SKA performance is realized, the perspective could usefully frame a new observational capability for studying low-level nonthermal processes in the quiet corona. The identification of past dynamic-range and PSF limitations is accurate and the emphasis on polarization and multi-wavelength association is well-motivated; however, the absence of any quantitative flux, size, or fidelity estimates means the significance assessment remains conditional on future verification.

major comments (1)

[Abstract] Abstract (and corresponding discussion of SKA capabilities): the central assertion that SKA sensitivity and snapshot PSF will detect and separate weak nonthermal quiet-corona emissions lacks supporting quantitative estimates of expected flux densities (Jy or mJy at 0.1-10 GHz), source sizes, brightness temperatures, or required dynamic range. Without these, or snapshot imaging simulations, it is not possible to verify that the claimed performance margin exists relative to thermal confusion and artifacts.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the constructive report. We agree that the manuscript would benefit from quantitative support for the projected SKA performance and will revise to address this.

read point-by-point responses

Referee: [Abstract] Abstract (and corresponding discussion of SKA capabilities): the central assertion that SKA sensitivity and snapshot PSF will detect and separate weak nonthermal quiet-corona emissions lacks supporting quantitative estimates of expected flux densities (Jy or mJy at 0.1-10 GHz), source sizes, brightness temperatures, or required dynamic range. Without these, or snapshot imaging simulations, it is not possible to verify that the claimed performance margin exists relative to thermal confusion and artifacts.

Authors: We accept the point that the absence of quantitative estimates weakens the central claim. The manuscript is a perspective piece that draws on documented SKA specifications and published limitations of prior instruments, but does not contain explicit flux, size, or dynamic-range calculations. In revision we will add such estimates to the abstract and main text, drawing on (i) reported flux densities of quiet-corona nonthermal events from recent VLA and MWA observations (typically 0.1–few mJy at 1–5 GHz), (ii) source angular sizes of a few arcseconds inferred from high-resolution imaging, (iii) corresponding brightness-temperature ranges, and (iv) the dynamic-range requirements (∼10^4–10^5) needed to separate them from the thermal background. These numbers will be referenced to the SKA sensitivity specifications and to the cited observational papers. Full end-to-end snapshot imaging simulations lie outside the scope of this review; we will instead cite existing SKA imaging-performance studies that address comparable dynamic-range and confusion issues. revision: yes

Circularity Check

0 steps flagged

No circularity: qualitative projection paper with no derivations or fitted inputs

full rationale

The manuscript is a forward-looking perspective on SKA capabilities for quiet-corona nonthermal emission studies. It contains no equations, no parameter fitting, no claimed derivations, and no load-bearing self-citations. All statements are qualitative assessments of future instrument performance relative to past observational limitations. No step reduces by construction to its own inputs; the central claims rest on expected SKA sensitivity and resolution rather than any self-referential logic. This is the expected non-finding for a non-derivational review-style paper.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

No mathematical model, free parameters, or new physical entities are introduced; the paper is an observational strategy discussion relying on standard knowledge of radio interferometry and solar corona properties.

pith-pipeline@v0.9.1-grok · 5852 in / 1346 out tokens · 31282 ms · 2026-07-02T05:55:59.062037+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

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