Solar energetic particles and their association with radio emissions

Anshu Kumari; Diana E. Morosan; Divya Paliwal; Eduard P. Kontar; Immanuel Jebaraj; Ketaki Deshpande; Mugundhan V.; Nina Dresing; Puja Majee

REVIEW 3 major objections 6 minor 6 references

Solar energetic particles and their association with radio emissions

T0 review · 3 major / 6 minor · reviewed 2026-08-02 · deepseek-v4-flash

Challenge this review Re-run · record.json Download PDF Read on arXiv ↗

Pith's one-line read This review argues that solar radio bursts, combined with SKA imaging and spectroscopy and with spacecraft particle measurements, can locate where and how solar energetic particles are accelerated—and the radio–SEP link remains the main mis

desk verdict A solid, honest review of SEP-radio connections and SKA prospects, but it is a review — no new science — and its central promise rests on the electron–ion link the authors themselves admit is unknown. read the letter →

arxiv 2603.28408 v2 pith:V7KO5VKG submitted 2026-03-30 astro-ph.SR physics.space-ph

Diana E. Morosan , Anshu Kumari , Immanuel Jebaraj , Eduard P. Kontar , Mugundhan V. , Ketaki Deshpande , Nina Dresing , Puja Majee

show 1 more author

Divya Paliwal

This is my paper

classification astro-ph.SRphysics.space-ph

keywords solarenergeticparticlestypeIIradioburstsIIIcoronalmassejectionsshockaccelerationflareimagingspectroscopySKA

verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

Solar energetic particles (SEPs) are accelerated either in flares or by shocks driven by coronal mass ejections, but where and how remains debated. This review argues that radio bursts—generated by low-energy electrons after they leave the acceleration site—are the best remote tracers of these processes, and that the Square Kilometre Array (SKA) can turn that into a quantitative tool. By combining SKA's high-resolution, spectro-polarimetric imaging with particle data from inner-heliosphere spacecraft, the timing, trajectory, and magnetic connectivity of escaping electron beams can be compared with inferred SEP injection times and energies. That comparison would let radio observations distinguish flare acceleration from shock acceleration, and pin down the acceleration regions of the protons and ions observed in space. The open caveat, acknowledged by the authors, is that the radio-emitting electrons and the higher-energy SEP ions may not share a common origin; the paper's whole program depends on that link being strong.

What carries the argument

The machinery is the radio burst itself, used as a remote tracer: type III bursts are produced by electron beams escaping along open magnetic field lines during flares, while type II bursts and herringbone fine structure trace electrons accelerated by CME-driven shock waves. The paper's method is to combine these signatures with interferometric imaging and spectro-polarimetry, matching the imaged radio source locations to interplanetary magnetic field lines that connect to spacecraft, and to compare radio onsets with particle injection times inferred from velocity dispersion at the spacecraft. SKA's contribution is the sensitivity, bandwidth, and imaging fidelity needed to follow a burst fro

What would settle it

A statistical survey of well-connected SEP events in the SKA era: if a significant fraction of >10 MeV proton events show no temporally associated type II or type III burst, or if type II bursts are imaged on field lines connected to a spacecraft that detects no protons, the common-origin assumption is falsified. Conversely, finding a one-to-one relation between radio burst onset and proton injection time in multi-event data would support it.

Watch

Extended reading notes

Core claim

In this review the authors set out to establish that the low-energy electron beams that produce solar radio bursts are a viable remote proxy for locating the acceleration of solar energetic particles, and that SKA observations are the step needed to make that proxy quantitative. They marshal evidence that type II bursts (from shock-accelerated electrons) and type III bursts (from flare-accelerated electrons) can be tied spatially and temporally to in situ electron events, that radio-derived densities and polarization can map the coronal environment and magnetic connectivity, and that inferred injection times from spacecraft can be compared with radio onsets to identify the accelerating mecha

Load-bearing premise

The load-bearing premise is that the low-energy electrons that produce the radio bursts are released from the same acceleration regions as the higher-energy protons and ions detected by spacecraft; the authors note that no proof of a common origin exists, and if the species are accelerated separately, radio timing and location would misidentify SEP acceleration sites.

Editorial extensions

If this is right

Type II bursts can be used to mark the presence of a CME-driven shock capable of accelerating ions, and type III bursts to mark flare-accelerated electron release; SKA's improved bandwidth and resolution will refine both diagnostics.
Combined SKA radio and spacecraft particle observations will allow the acceleration time, trajectory, and escape of low-energy electrons to be determined from the corona into the heliosphere.
Radio-derived electron densities and magnetic field strengths, corrected for scattering, will provide quantitative plasma parameters (density, Alfvén speed, Mach number, shock geometry) relevant to SEP acceleration.
The association between type II burst bandwidth and SEP peak flux, if confirmed with more events, strengthens the common-origin picture between the radio-emitting electrons and the SEPs.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

If the radio–SEP link holds, the same SKA-era technique could be applied to stellar flares on other stars: their radio bursts could be used to infer the acceleration of energetic particles in stellar coronae and the space-weather environment of exoplanets.
The paper's acknowledged uncertainty—that radio-emitting electrons and SEP protons may not share a source—could be resolved by a dedicated SKA-era campaign targeting well-connected events and comparing proton injection times with type II/III onsets; a systematic mismatch would force a re-think of which species the radio actually traces.
The delays between type III onsets and near-relativistic in situ electron arrivals documented in the review suggest radio timing tracks first escape while in situ onsets include transport effects; SKA imaging near the acceleration region could separate the two, sharpening SEP release time estimates used in space-weather models.
Should the radio–SEP link fail for protons specifically, SKA's radio diagnostics would still provide a reliable tool for solar energetic electrons, which matter in their own right for radiation hazards in space.

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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Desk Editor's Note

read the letter

Take the reader's UNVERDICTED seriously only if you are asking whether the paper contains a new research result. It does not. But that is the wrong question for this manuscript. It is a review and a SKA science-case chapter, and on that genre it does well.

The paper is well organized, current, and genuinely honest about the messiness of linking radio bursts to SEPs. It flags the 2–3 orders of magnitude electron number deficit, the timing delays between type III onsets and near-relativistic in-situ onsets, the broken spectra, and the fact that radio emission traces escaped electron populations, not the acceleration volume itself. The authors also acknowledge that SKA performance depends on deployment stage. That level of candor is earned and it is the best thing about the paper.

The soft spot is exactly the one the stress-test identifies. The central programmatic claim in §4 — that SKA will bridge coronal radio diagnostics and in situ particle measurements to determine where and how SEP protons and ions are accelerated — requires that the low-energy electrons generating type II and type III bursts be co-accelerated with those ions. Section 3.1 states plainly that this is unknown. The paper does not hide this, but the caveat sits in a different section than the promise. A careful referee should ask the authors to carry that caveat into the abstract or at least the opening of §4, because a casual reader could overstate what the SKA will actually deliver.

Other concerns are minor. The self-citation count is high, but the authors are central to this subfield and the citations are mostly appropriate. There is no new data, no derivations, no fabricated numbers — nothing to catch on circularity. There are occasional typos (e.g., 'Aflvén').

Who is this for? Researchers planning SKA solar observing programs, and anyone wanting a current map of the open questions in SEP-radio physics. It will not change anyone's physics, but it is a useful, honest reference.

My recommendation: send it to peer review as a review article. It deserves a serious referee, mainly to check coverage and to push the authors to make the electron–ion link caveat unavoidable in the summary.

Referee Report

3 major / 6 minor

Summary. The manuscript is a review/prospectus, not an original research paper. It argues that low-frequency radio bursts (type II/III, continua) produced by accelerated electrons, observed with SKA's planned sensitivity, dynamic range, and spectro-polarimetric imaging, can be combined with multi-spacecraft in situ particle measurements (Solar Orbiter, PSP, Wind, etc.) to identify where and how solar energetic particles are accelerated. It surveys current ground- and space-based facilities, discusses recent case studies and known discrepancies between remote and in situ diagnostics, and outlines SKA's anticipated contribution. No new quantitative analysis or model is presented.

Significance. This is a useful, up-to-date synthesis, particularly valuable for collecting recent results (LOFAR/MeerKAT imaging, PSP/Solar Orbiter particle and radio data, CoSEE-Cat) and for the authors' explicit caveats in §3.1 and §3.3 about the unknown electron–ion link and order-of-magnitude discrepancies. It will be a helpful community reference if revised. However, its central claim—that SKA will determine where and how SEPs are accelerated—is programmatic rather than demonstrated. The manuscript contains no quantitative predictions, error budgets, or falsifiable tests, which is appropriate for a white paper but limits its weight as a journal article. Credit is due for being honest about several limitations that directly qualify the headline promise.

major comments (3)

[§4.1, §4.3, §4.4] There is an internal contradiction about what radio imaging can deliver. §4.1 promises 'imaging of the acceleration process (via SKA radio data)' and §4.4 states SKA will enable 'the direct identification and morphological characterization of coronal particle acceleration sites.' Yet §4.3 correctly caveats that 'Solar radio bursts generally do not directly image the particle acceleration region itself; instead, coherent radio emission traces the non-thermal electron populations after they escape from the acceleration site.' Because the paper's headline promise is identification of SEP acceleration regions, this contradiction is load-bearing. Please rephrase the stronger statements as 'acceleration-related' or 'escape/accelerated-electron regions,' or explain how the intrinsic acceleration volume can be reconstructed from tracers that are observed only after escape.
[§3.1, §3.3, §4] The proposed SKA-based identification of SEP ion acceleration sites assumes a common origin for radio-emitting low-energy electrons and high-energy ions. The paper itself states in §3.1 that 'it is also unknown if the lower-energy electrons (such as the ones producing type II bursts) and the energetic protons have a common origin,' and §3.3 documents serious discrepancies—2–3 order-of-magnitude number deficits, type-III-to-in-situ onset delays, and broken in situ electron spectra—between radio/HXR electrons and in situ electrons. The abstract's claim that radio observations 'can be used to distinguish between flare and shock acceleration' therefore overstates current certainty. I do not regard the common-origin assumption as disproven, but the manuscript should either soften the central claim to 'may test the link' or specify a concrete multi-messenger test (e.g., comparing radio-inferre
[§4, Table 3] The paper does not provide a quantitative feasibility analysis connecting SKA's technical parameters to the required measurements. For example, it asserts unrivaled sensitivity and resolution but does not estimate the expected angular sizes of type II/III sources at SKA frequencies, the minimum detectable electron flux at a given heliocentric distance, or the uv-coverage and cadence needed to localize bursts relative to in situ field-line connections. Without such an error budget, the central claim that SKA 'will bridge the gap' remains an assertion. Adding at least one worked quantitative example—or explicitly stating that this is outside the paper's scope—would substantially strengthen the programmatic argument.

minor comments (6)

[§2.1] Figure cross-reference appears wrong: the frequency-coverage and operational-period summary is Fig. 1, not Fig. 4 as printed.
[§3.8] 'Inn summary' should be 'In summary.'
[§4.2] Typos: 'Aflvénspeed,AflvénivMachnumbers' should be 'Alfvén speed, Alfvénic Mach numbers.'
[Table 3] 'Adityia-1' should be 'Aditya-L1.'
[Table 1] Header 'Operational Y ears' contains a stray space.
[§1, §3.3] Scattered typos include 'herrignbones'/'errignbones' and 'burts' in §1, and inconsistent 'Cosee-Cat'/'CoSEE-Cat' spellings in §3.3 and Figure 6.

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity: the paper is a literature synthesis with no derived predictions; its central SKA promise is explicitly conditioned on an acknowledged open question.

full rationale

This is a review/prospects article, not a derivation paper. It performs no fitting, no equation-level derivation, and no quantity is defined in terms of another. The strongest claim, that SKA will bridge coronal radio diagnostics and in situ particle measurements, is presented as a programmatic expectation rather than as a predicted result derived from inputs. The paper explicitly acknowledges the assumption underlying that claim: in §3.1 it states that 'the origin at the Sun of high-energy SEPs is unknown and thus, it is also unknown if the lower-energy electrons (such as the ones producing type II bursts) and the energetic protons have a common origin.' Section 3.3 further documents timing, number, and spectral discrepancies between radio-emitting and in situ electrons, which is an honest statement of an open problem, not a circular reduction. Author self-citations appear frequently, but they function as ordinary references to specific published observations (e.g., Morosan et al. 2025a connecting imaged type II sources to Solar Orbiter electron detections) and do not serve as unverified uniqueness theorems, smuggled ansatze, or fitted parameters renamed as predictions. No load-bearing step reduces to its own input, so there is no significant circularity.

Assumptions & free parameters 0 free parameters · 3 assumptions · 0 invented entities

The paper's argument rests on standard solar radio physics, the assumed radio–SEP connection (which it flags as uncertain), and future instrument performance. No free parameters or invented entities appear.

assumptions (3)

domain assumption Type III and type II radio bursts are generated by non-thermal electron beams via beam-plasma instabilities.
Standard solar physics assumption invoked throughout to link radio emission to electron acceleration (Sections 1 and 3).
domain assumption Radio-emitting low-energy electrons share a common origin or are related to higher-energy SEPs (protons/ions) observed in situ.
The central programmatic claim relies on this connection, but the paper itself notes it is still open in §3.1.
domain assumption SKA will achieve the predicted sensitivity, imaging fidelity, and frequency coverage for solar observations.
The paper states performance depends on staged deployment (AA4, AA*) and notes practical constraints in §4.3.

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Cite this review

Pith. "Pith review of Solar energetic particles and their association with radio emissions." pith.science (2026). https://pith.science/paper/V7KO5VKG

@misc{pith2026260328408,
  author       = {Pith},
  title        = {Pith review of: Solar energetic particles and their association with radio emissions},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/V7KO5VKG}},
  note         = {Machine review of arXiv:2603.28408}
}

read the original abstract

Energetic particle populations are ubiquitous throughout the Universe. In our solar system, the most prominent sources of energetic particles are solar flares or collisionless shocks often driven by huge eruptions of magnetised plasma called coronal mass ejections (CMEs). Remotely, low energy electrons from the Sun can be observed as solar radio bursts that are produced by accelerated electron beams undergoing beam-plasma interactions. There are still many open questions on the generation of solar energetic particles (SEP): how and where are SEPs accelerated during solar flares and CMEs and how they escape the solar atmosphere? Another important question is: what is the link between the solar radio bursts and the observed SEPs at spacecraft? SKA can provide high-resolution radio images combined with spectroscopic observations to determine the acceleration time, trajectory and escape of low energy electrons from the solar corona. The synergy between SKA and current space missions will help investigate solar activity and energetic particles across a wide range of wavelengths and particle energies. Particle data from spacecraft can be used to make a connection between radio bursts and SEPs by comparing SEP inferred injection times and energies to those of electrons generating radio bursts at the Sun. Radio observations in turn can be used to distinguish between flare and shock acceleration since different radio bursts pinpoint towards different energetic processes. Since the acceleration region and origin of SEPs of various properties is still largely debated, radio observations have the potential to be an invaluable tool in unraveling these processes.

Figures

Figures reproduced from arXiv: 2603.28408 by the authors.

**Figure 1.** Frequency coverage and operational periods of major solar radio imaging instruments worldwide. The plot illustrates the long-term continuity and complementary frequency ranges of facilities from metric to microwave wavelengths Together, these observatories provide multi-frequency imaging coverage of the solar atmosphere over several decades, enabling studies of radio bursts, active regions, and coronal dynamics acro… view at source ↗

**Figure 2.** Typical daily observation windows and frequency coverage of solar radio imaging instruments. Each shaded region represents the frequency band and local observing time (in Universal Time) for facilities across different longitudes. The plot highlights the near-continuous global coverage achieved through coordinated observations from Asia (GRAPH, DART, CSRH), Europe (NRH, RATAN-600, SunDish, MRO, SRH), and the America… view at source ↗

**Figure 3.** SolarMACH plot showing the current constellation of spacecraft monitoring the Sun (Gieseler et al., 2023). Multiple spacecraft are also located close to Earth. The solid spirals show the magnetic connections of each spacecraft and the Earth to the Sun along the interplanetary magnetic field. While all these remote sensing observations and in situ measurements provide insights on the solar activity, radio observation… view at source ↗

Figures from the paper (3 more)

**Figure 4.** Figure 4: Connecting remote radio and X-ray observations to solar energetic electrons. a. Three-dimensional representation of the electron acceleration signatures (hard X-rays and Type II radio bursts) that occurred during a CME eruption of 3 October 2023. The purple mesh repres…

**Figure 5.** Figure 5: Coronal Mass Ejections (CME) and signatures of accelerated electrons. (a) SDO/AIA 171 Å image at 11:20:57 UT, superimposed with a potential field source surface (PFSS) extrapolation at noon showing both open (blue) and closed (white) field lines within region surroundi…

**Figure 6.** Figure 6: Energetic electrons observed from 10 keV to 1 MeV (top panel), the radio dynamic spectrum showing a type III radio burst close to the electron release time and the X-ray light curves in five different energy bands from 4 to 84 keV. This is one of the many energetic ele…

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Works this paper leans on

6 extracted references · 1 canonical work pages

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Pith tools

Reviewed August 2, 2026 · model on record in the stance chip above.

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doi: 10.3847/1538-4357/adee25. A. Voshchepynets and V. Krasnoselskikh. Electron beam relaxation in inhomogeneous plasmas. Annales Geophysicae, 31(8):1379–1385, Aug. 2013. doi: 10.5194/angeo-31-1379-2013. A. Voshchepynets and V. Krasnoselskikh. Probabilistic model of beam-plasma interaction in randomly inhomogeneous solar wind.Journal of Geophysical Resear...

arXiv 2013

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Observations indicate that thecoronaoverlyingtypeIIIproducingsitesiscomposedofsmall,discrete,over-densestructures, suggesting that the bursts may propagate along such regions

Research supported by the Centre National d’Etudes Spatiales. Observations indicate that thecoronaoverlyingtypeIIIproducingsitesiscomposedofsmall,discrete,over-densestructures, suggesting that the bursts may propagate along such regions. R. Vainio, E. Valtonen, B. Heber, O. E. Malandraki, A. Papaioannou, K.-L. Klein, A. Afanasiev, 38 Solar energetic parti...

arXiv 1996

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doi: 10.1007/s11207-019-1518-3. M. L. Kaiser, T. A. Kucera, J. M. Davila, O. C. St. Cyr, M. Guhathakurta, and E. Christian. The STEREO Mission: An Introduction. Space Sci. Rev., 136(1-4):5–16, Apr. 2008. doi: 10.1007/s11214-007-9277-0. D. Kansabanik, D. Oberoi, and S. Mondal. Probing coronal magnetic fields using high fidelity low-frequency spectro-polari...

work page Pith review arXiv doi:10.48550/arxiv.2207.11924 2008

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doi: 10.3847/1538-4357/adaa7c. R. Miteva, S. W. Samwel, and S. Zabunov. Solar Radio Bursts Associated with In Situ Detected Energetic Electrons in Solar Cycles 23 and 24.Universe, 8(5):275, May 2022. doi: 10.3390/ universe8050275. A. Mohan, P. Mäkelä, N. Gopalswamy, S. Akiyama, and S. Yashiro. Role of CME Clusters and CME-CMEInteractionsinProducingSustain...

arXiv 2022