{"id":"c3644bc8-c8f4-4e35-92e7-960690e6f21a","arxiv_id":"2502.06332","paper_version":1,"verdict":"CONDITIONAL","confidence":"HIGH","novelty_score":7.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"A single far-side solar eruption likely drove a circumsolar interplanetary shock that produced the 13 March 2023 widespread energetic storm particle event seen at six spacecraft.","lead":"A solar eruption on the far side of the Sun on 13 March 2023 sent out an interplanetary shock and energetic particles that were observed at six spacecraft spread across the inner heliosphere. The authors use MHD simulations to argue that a single circumsolar shock wave, rather than a series of earlier eruptions, is the most likely explanation for this energetic storm particle event.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The blast-wave timing agreement is partly circular: the 0.1 au, 3000 km/s, 05:00 UT injection is tuned to the event, so a sensitivity scan is needed before accepting the circumsolar scenario.","rationale":"The reader's CONDITIONAL verdict is appropriate. My pass identifies the same broad soft spot identified by the reader: the circumsolar blast-wave scenario is credible but not proven, and the source-region inference is indirect. However, I sharpen the concern: the most load-bearing assumption is not merely that the far-side eruption launched a spherical, driverless shock, but that the EUHFORIA implementation of that idea is a genuine test. Inserting a spherical blast wave at 0.1 au at 05:00 UT with 3000 km/s gives the simulation two free parameters whose main observable consequence is precisely the arrival time at every front-side observer. Matching those times is therefore partly circular unless the parameter choice is shown to be robust or independently constrained by data not used in the fit. The paper does not report such a sensitivity study, so the claimed 'slightly better' performance of the blast-wave scenario is not yet quantitatively established relative to the pre-CME scenario. Even so, the paper contains real independent evidence: shock normals pointing radially outward at all observers, the absence of clear ejecta drivers at Earth and STEREO A, the consistency of shock-speed decay with a Sedov-like scaling, and the coronagraphic appearance of a wave surrounding the Sun. These observations make the circumsolar scenario more than a pure simulation artifact. Thus the correct status remains CONDITIONAL: the scenario is plausible and partially supported, but the quantitative timing argument needs the sensitivity check I propose before the conclusion can be accepted as definitive.","tokens_in":36033,"tokens_out":3834,"duration_ms":39024,"concrete_test":"Run a sensitivity ensemble over the blast-wave injection: vary t_inject over at least +/-60 minutes around 05:00 UT and V_inject over the physically motivated range 2000-4000 km/s (including the 1-sigma range 2800 +/- 300 km/s from Jebaraj et al. 2024a), holding the solar wind background, pre-event CMEs, and all other setup fixed. Record the shock arrival-time residuals at BepiColombo, Solar Orbiter, STEREO A, and L1 for each member. If the spread of arrival residuals across the ensemble exceeds the claimed 1.5 h / 3 h margins, the agreement is a fitting artifact and the circumsolar scenario should be presented as untested by the timing comparison; if the residuals remain within the claimed margins across the ensemble, the conclusion is robust.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The paper's central claim, that a single circumsolar blast wave is a realistic explanation of the 13 March 2023 ESP event, rests mainly on the EUHFORIA result (Sect. 3.3) that a spherical shock arrives within about 1.5 hours at BepiColombo, Solar Orbiter, and STEREO A, and about 3 hours early at L1. The load-bearing problem is that this simulation is not a forward test of the blast-wave hypothesis: the blast wave is inserted simultaneously at the entire inner boundary at 0.1 au at 05:00 UT with an initial speed set to 3000 km/s. Both parameters are chosen, or at least strongly informed, so that the shock reaches the front-side observers near the observed times. The 05:00 UT injection time is roughly 1h47m after the inferred eruption onset, and the 3000 km/s speed is taken from the near/flank-side Parker in-situ shock measurement; neither value is independently derived for the driverless, front-side portion of the wave. The spherical shape is an assumption, not a demonstrated property of the real disturbance. Consequently, matching three to four arrival times within a few hours has weaker evidential force than claimed: a spherical blast with two free parameters (launch time and initial speed) can be tuned to a handful of arrival times. The 'slightly better' comparison with the pre-CME scenario is also qualitative and lacks uncertainty quantification, especially since the pre-CME scenario itself required a tenfold density enhancement to work. The independent observational support (radial shock normals, absent clear drivers at Earth and STEREO A, Sedov-like speed decay) is genuine but does not establish that the far-side eruption generated a coherent, spherical, driverless shock persisting to 1 au. The timing agreement therefore cannot bear the full weight of the conclusion unless it is shown robust to the chosen injection parameters.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper analyzes the extreme widespread solar energetic particle (SEP) event of 13 March 2023, observed by six well-separated spacecraft, with in-situ shock crossings and energetic storm particle (ESP) signatures at all inner-heliospheric observers. Because the source eruption occurred on the far side as seen from Earth, its location is inferred indirectly from radio bursts, hard X-ray data, and active-region tracking before and after the event. The authors characterize the SEP intensities, anisotropies, injection times, and shock parameters at each spacecraft, then use EUHFORIA MHD simulations to test two scenarios: (1) a single circumsolar, partly driverless blast wave from the main eruption, and (2) a pre-event CME (CME5) whose flank shock, with an ad hoc density enhancement, re-accelerates particles from the main eruption. Both simulations reproduce the observed shock arrival times roughly, and the authors state that the blast-wave scenario performs slightly better. The central conclusion is that a circumsolar ESP event driven by a single eruption is a realistic scenario.","tokens_in":36351,"tokens_out":3840,"duration_ms":39590,"significance":"If the circumsolar-shock interpretation is accepted, this is a remarkable event: an ESP event and shock crossings at six locations spanning more than 150 degrees in longitude, including a possible driverless shock at 1 au. The paper's main strengths are the detailed multi-mission data characterization, the careful shock-normal and anisotropy analysis, the inclusion of six pre-/post-event CMEs in the EUHFORIA setup, and the explicit attempt to compare two competing scenarios rather than simply asserting a single explanation. The candid discussion of source-region ambiguity and of the ad hoc density enhancement in the CME5 scenario is also commendable. However, the scenario discrimination rests on a small number of arrival-time comparisons, and the blast-wave simulation is initialized with values derived from the same event, so the evidence is more suggestive than demonstrative.","major_comments":[{"comment":"The blast-wave simulation is not an independent forward test of the circumsolar hypothesis. The injection time (05:00 UT) and initial speed (3000 km/s) at 0.1 au are explicitly chosen to be consistent with the inferred eruption onset and the Parker in-situ shock speed, respectively. With two free parameters, matching four arrival times within a few hours provides only weak discriminating power. Please add a sensitivity scan over injection time, injection speed, and (if feasible) the assumed spherical symmetry, showing how the arrival-time residuals at BepiColombo, Solar Orbiter, STEREO A, and L1 change over plausible parameter ranges. Without such a scan, the claim that the blast-wave scenario is \"realistic\" and \"matches the observations exceptionally well\" is not yet fully supported.","section":"Section 3.3"},{"comment":"The comparison between the two scenarios is qualitative. The statement that the blast-wave scenario performs \"slightly better\" is not supported by a quantitative metric, error bars, or a discussion of model uncertainty, and the pre-CME scenario only works after increasing CME5's density by an order of magnitude. Please report arrival-time residuals with uncertainties for both scenarios at each spacecraft, and state explicitly whether the \"slightly better\" conclusion survives when the model's known limitations (e.g., no magnetic structure in cone CMEs, uniform background solar wind) are taken into account.","section":"Sections 3.3 and 3.4"},{"comment":"The source region of the eruption is inferred to lie within a 56-degree-wide sector spanned by two active regions, with no direct imaging of the eruption itself. The circumsolar blast-wave scenario assumes a specific eruption time (03:13 UT) and a roughly spherical shock from this sector. The paper should discuss how sensitive the simulated arrival times are to the assumed source location within the AR1/AR2 sector and to the uncertainty in the eruption onset time, since all front-side observers are more than 100 degrees away from either edge of the sector. This is directly relevant to the central claim that a single circumsolar shock is the most plausible explanation.","section":"Section 2.1 and Appendix B"},{"comment":"The blast-wave insertion methodology, including the Rankine-Hugoniot mapping and the modified Sedov scaling, is described as being detailed in Wijsen et al. (2025), which is listed as submitted. Since the central scenario relies on this methodology, the present paper is not fully self-contained. Please either include the essential details and validation of the blast-wave model in this manuscript or, if the companion paper is essential, indicate how its results support the specific choices made here (e.g., the 0.1 au injection height and the self-similar decay assumption).","section":"Section 3.3"}],"minor_comments":[{"comment":"There are several typographical errors in this section, including \"Furhtermore\" and \"measuremnets\" in the MAVEN paragraph; these should be corrected.","section":"Section 3.1"},{"comment":"In the paragraph reporting arrival-time agreement, \"BepiColomobo\" should be \"BepiColombo\".","section":"Section 3.3"},{"comment":"The sentence \"Theyat it was near-parallel\" appears garbled; it should likely read \"They found it was near-parallel.\" Please revise.","section":"Section 2.3"},{"comment":"The sentence about the gray shade in the Mars plot is grammatically incomplete: \"The gray shade in the Mars plot represents the CME arrival time based on the pre-event CME simulation, is the CME of the main eruption.\" Please clarify which structure is represented.","section":"Figure 6 caption"},{"comment":"For MAVEN, the text in Appendix D uses a path length based on 350 km/s, while Table 1 lists 325 km/s from Mars Express. Please harmonize these values and explain any difference.","section":"Table 1 and Appendix D"}],"recommendation":"major_revision","confidential_remarks":"The paper is a valuable multi-spacecraft case study, and the scenario comparison is appropriate for A&A. The main risk is the circularity of the blast-wave setup: two of its key parameters are derived from the same event, and the paper lacks a sensitivity study. A major revision that adds such a study, quantifies the scenario comparison, and addresses the source-region ambiguity would substantially strengthen the central claim. I do not think rejection is warranted, because the observational characterization alone is a significant contribution and the conclusions are appropriately hedged in most places. The reliance on a submitted companion paper (Wijsen et al. 2025) for the blast-wave methodology is another point to flag to the editor, as it affects the paper's self-containedness."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague,\n\nThe paper is a careful multi-spacecraft study of the 13 March 2023 ESP event, and it makes a genuinely new claim: a single far-side eruption can drive a circumsolar IP shock that stays coherent enough to 1 au to produce ESP events at six well-separated spacecraft. The dataset is the strongest part. Parker, Solar Orbiter, BepiColombo, STEREO A, L1, and MAVEN all saw the event; the shock normal analysis shows roughly radial propagation everywhere; Earth and STEREO A see no clear driver behind the shock, which is what a freely propagating wave should look like; and the observed speed decay is consistent with a Sedov-like blast. The authors also test the sensible alternative, a pre-event CME flank, and are honest that both scenarios can explain the observations, with the blast wave doing 'slightly better'.\n\nThe soft spot is where the stress-test lands: the EUHFORIA blast wave is inserted at 0.1 au at 05:00 UT with an initial speed of 3000 km/s, and both numbers are taken from the same event—the Parker shock measurement and the inferred eruption onset. That makes the arrival-time agreement a consistency check, not an independent prediction. With two tuned parameters and four arrival times, the match is encouraging but not decisive. The paper would be much stronger with a sensitivity scan over the injection speed and time, and with some quantitative measure of how much better the blast wave fits than the CME5 scenario. The pre-CME case is also not on equal footing because it requires a ten-fold density enhancement to work, a point the authors acknowledge.\n\nI don't think this is a load-bearing flaw. The simulation setup is physically motivated, the supporting observations are real, and the conclusions are properly hedged—they say 'realistic scenario', not 'proven'. The main gap is that the claiming is slightly ahead of the evidence. A revision that adds robustness testing and tighter uncertainty language would move this from a very good event study to a reference case.\n\nSend it to a good referee. It deserves time, and it will be cited.","headline":"First credible multi-spacecraft case for a circumsolar shock to 1 au, but the timing fit is a consistency check with tuned parameters, not a forward test.","tokens_in":37108,"tokens_out":3109,"would_cite":true,"duration_ms":28753,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"This paper argues that a single solar eruption from the Sun's far side can drive a circumsolar shock, producing an energetic storm particle event observed all around the Sun, and that the blast-wave scenario matches observed shock arrival…","keywords":["solar energetic particles","energetic storm particle event","circumsolar shock","CME-driven shock","blast wave","EUHFORIA simulation","multi-spacecraft SEP event","March 2023 flare"],"falsifier":"A spacecraft with a direct view of the far-side Sun at that time could check whether the eruption indeed occurred at 03:13 UT in the inferred sector; if the source time or location differed, the blast-wave timing agreement at the front-side spacecraft would disappear.","tokens_in":35835,"feed_emoji":"☀️","tokens_out":7011,"duration_ms":62046,"temperature":0.7,"pith_summary":"On 13 March 2023, a large solar eruption on the Sun's far side produced an energetic particle event observed at six well-separated spacecraft, and an energetic storm particle (ESP) event at every inner-heliospheric observer, implying the driving shock wrapped around the Sun. The authors test two explanations with magnetohydrodynamic simulations: a single circumsolar blast wave launched by the eruption, or a pre-event CME flank encountering the front-side spacecraft. Both settings reproduce the observations, but the blast-wave scenario matches the observed shock arrival times at the front-side spacecraft within about 1.5 hours (about 3 hours early at L1). The paper concludes that a circumsolar ESP event driven by a single eruption into the inner heliosphere is a realistic scenario.","feed_headline":"A single far-side eruption can explain an all-around-Sun particle storm","feed_subtitle":"Simulations match shock arrivals at five spacecraft within hours, supporting a single circumsolar origin.","key_machinery":"The central tool is the EUHFORIA magnetohydrodynamic model of the inner heliosphere, run with and without a spherical blast wave inserted at the 0.1 au inner boundary at 05:00 UT on 13 March, with an injected speed of 3000 km/s obtained from Rankine–Hugoniot jump conditions and consistent with the near-Sun shock speed measured by Parker. The blast wave is assumed to expand self-similarly in the Sedov-like manner, with shock speed falling as t^−1/3, and the comparison scenario injects the pre-event CME5 with a density ten times the default EUHFORIA value. In-situ shock parameters—normal direction, speed, Mach number, and geometry—derived from multi-spacecraft data tie the observations to the two simulations.","core_discovery":"The paper claims that the widespread ESP event of 13 March 2023 can be explained by a single eruption from the far side that launches a spherical, driverless shock, which expands self-similarly and remains strong enough to be seen in situ at five inner-heliospheric spacecraft spanning about 153 degrees of longitude. It supports this by comparing EUHFORIA simulations—where a 3000 km/s blast wave is inserted at 0.1 au—with the observed shock arrivals and plasma signatures at Parker Solar Probe, BepiColombo, Solar Orbiter, STEREO A, near-Earth spacecraft, and MAVEN. The alternative scenario, in which a pre-event CME (CME5) with an order-of-magnitude-increased density sends its flank toward the front-side observers, also reproduces the observations but matches the shock arrival times slightly less well.","pith_inferences":["If circumsolar blast waves are a real phenomenon, the historical rarity of 'widespread' SEP events may partly reflect sparse far-side spacecraft coverage rather than the intrinsic rarity of the event; the current multi-spacecraft fleet could reveal such events more often.","The energy budget implied by a 3000 km/s blast wave that still arrives at 1 au is substantial, and computing the total energy available from the inferred far-side flare and CMEs would provide a testable constraint on whether such a wave is energetically plausible for this or future events.","The inverse velocity dispersion observed by BepiColombo and Solar Orbiter could be a generic signature of a spacecraft that only later becomes magnetically connected to an accelerating shock flank, rather than of particle transport effects; dedicated transport simulations could test this interpretation.","The paper leaves open whether the far-side shock front is a single coherent surface or the sum of two merged shocks from the two simultaneously erupting CMEs; future multi-spacecraft shock-normal measurements could map the shape of such a circumsolar front."],"forward_implications":["If a single eruption can make a circumsolar ESP event, then front-side spacecraft can observe ESP events from far-side eruptions, so SEP forecasting should treat circumsolar shocks as a possible source class.","The blast-wave simulation's arrival-time agreement (within about 1.5 h at BepiColombo, Solar Orbiter, and STEREO A, and about 3 h early at L1) means a simple Sedov-like decay law can predict 1 au shock arrival from a near-Sun shock speed.","The alternative scenario would require CME5 to be about ten times denser than EUHFORIA's standard value, so a typical pre-event CME alone would not produce the observed front-side ESP event.","Distinguishing the two scenarios observationally requires checking for a driverless shock (no ejecta at Earth and STEREO A) versus flank-encounter signatures (possible ejecta remnants at BepiColombo and Solar Orbiter)."],"supporting_citations":[{"why":"Provides the near-Sun in-situ shock speed of about 2800–3000 km/s and shock strength used to calibrate the injected blast wave in the simulation.","marker":"Jebaraj et al. (2024a)"},{"why":"Supplies the modified Sedov self-similar scaling and the method for inserting blast waves into EUHFORIA, upon which the circumsolar scenario's arrival-time predictions rest.","marker":"Wijsen et al. (2025)"},{"why":"Introduces the EUHFORIA model itself, the framework used for both scenarios.","marker":"Pomoell & Poedts (2018)"},{"why":"Defines the spheromak CME model used in EUHFORIA for the main eruption's two CMEs (CMEa and CMEb).","marker":"Verbeke et al. (2019)"},{"why":"Provides the graduated cylindrical shell reconstruction technique used to fit the pre-event CMEs, including CME5, giving the parameters inserted in the simulations.","marker":"Thernisien et al. (2009)"},{"why":"The 23 July 2012 event is the comparison case where the spherical shock decayed rapidly in the wake region, contrasting with the long survival inferred here.","marker":"Liu et al. (2017)"},{"why":"The self-similar point-explosion solutions whose modification underlies the assumed t^−1/3 shock-speed decay law.","marker":"Sedov (1946)"}],"fun_headline_variants":["One far-side blast can spark a global particle storm","Far-side eruption alone explains all-around Sun particle event","Single eruption drives shock seen around entire inner heliosphere","Model shows one CME can create circumsolar particle storm"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that the far-side eruption at 03:13 UT, whose source sector is inferred from radio bursts and active-region imaging rather than directly seen, launches a spherical, driverless shock that keeps its self-similar expansion all the way to 1 au.","fun_headline_variants_meta":{"raw":{"variants":["One far-side blast can spark a global particle storm","Far-side eruption alone explains all-around Sun particle event","Single eruption drives shock seen around entire inner heliosphere","Model shows one CME can create circumsolar particle storm"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000555,"raw_usage":{"total_tokens":2703,"prompt_tokens":1068,"completion_tokens":1635,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":684,"completion_tokens_details":{"reasoning_tokens":1569}},"tokens_in":684,"tokens_out":1635,"duration_ms":9542,"temperature":1.0,"reasoning_tokens":1569,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-08T15:47:12.882993+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A spacecraft with a direct view of the far-side Sun at that time could check whether the eruption indeed occurred at 03:13 UT in the inferred sector; if the source time or location differed, the blast-wave timing agreement at the front-side spacecraft would disappear.","supporting_citations":[{"cited_title":"2025, , submitted","cited_arxiv_id":null,"evidence_quote":"Supplies the modified Sedov self-similar scaling and the method for inserting blast waves into EUHFORIA, upon which the circumsolar scenario's arrival-time predictions rest."},{"cited_title":"& Poedts , S","cited_arxiv_id":null,"evidence_quote":"Introduces the EUHFORIA model itself, the framework used for both scenarios."},{"cited_title":"2019, , 627, A111","cited_arxiv_id":null,"evidence_quote":"Defines the spheromak CME model used in EUHFORIA for the main eruption's two CMEs (CMEa and CMEb)."},{"cited_title":"D., Hu , H., Zhu , B., Luhmann , J","cited_arxiv_id":null,"evidence_quote":"The 23 July 2012 event is the comparison case where the spherical shock decayed rapidly in the wake region, contrasting with the long survival inferred here."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"The self-similar point-explosion solutions whose modification underlies the assumed t^−1/3 shock-speed decay law."}],"review_version":1}