arxiv: 2605.06805 · v1 · submitted 2026-05-07 · 🌌 astro-ph.SR · astro-ph.GA

Recognition: 2 theorem links

· Lean Theorem

Radio Continuum and Water Maser Monitoring of the Outburst in HOPS 373: Free-Free Emission Does Not Respond to the Outburst

John Tobin , Doug Johnstone , Greg Herczeg , Jeong-Eun Lee , Ho-Gyu Lee , Carlos Contreras-Pena , Sung-Yong Yoon , Steve Mairs

Authors on Pith no claims yet

Pith reviewed 2026-05-11 00:47 UTC · model grok-4.3

classification 🌌 astro-ph.SR astro-ph.GA

keywords protostarsoutburstsfree-free emissionradio continuumwater masersaccretionOrionHOPS-373

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The pith

Free-free radio emission from the protostar HOPS-373 shows no detectable change during its luminosity outburst.

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

The paper presents VLA monitoring of radio continuum and water masers from HOPS-373, a binary Class 0 protostar that experienced a roughly fourfold luminosity increase. No variation appears in the 5 cm free-free continuum either at outburst peak or during decline, and the 1.3 cm emission between the binary components remains steady. Water masers vary in velocity and position near the southwest source but lack a clear tie to the luminosity event. The observations indicate that free-free emission, which traces ionized outflow gas, does not directly track the accretion-driven burst.

Core claim

We do not find evidence for a change in the free-free emission traced by VLA 5 cm continuum during the peak of its outburst or during the decline. The lack of correlation between outburst and free-free emission from HOPS-373 indicates that the free-free emission may not directly respond to increases in the accretion rate and subsequently the outflow rate. The lack of a link could be due to the outflow mostly being neutral, or there may be offsets in the timescale for the free-free response.

What carries the argument

VLA C-band (5 cm) continuum monitoring combined with K-band (1.3 cm) continuum and 22 GHz water maser observations of HOPS-373 over two years.

If this is right

Free-free emission may not respond directly to accretion-rate increases that drive the outburst.
The protostellar outflow may remain mostly neutral rather than ionized.
A time offset could exist between the luminosity burst and any eventual free-free response.
Multi-frequency radio monitoring of other outbursting protostars can test whether this decoupling is typical.

Where Pith is reading between the lines

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

If free-free emission is insensitive on these timescales, radio surveys may miss short-term accretion events in embedded sources.
Longer baseline observations could distinguish between a neutral outflow and a delayed ionization response.
Models of jet launching in Class 0 objects may need to incorporate a neutral component that does not produce immediate radio signatures.

Load-bearing premise

Any response in free-free emission to the outburst would be detectable within the monitoring period, sensitivity, and frequency coverage of the VLA observations.

What would settle it

A statistically significant rise in 5 cm continuum flux from HOPS-373 measured in a later VLA epoch after the current monitoring window.

Figures

Figures reproduced from arXiv: 2605.06805 by Carlos Contreras-Pena, Doug Johnstone, Greg Herczeg, Ho-Gyu Lee, Jeong-Eun Lee, John Tobin, Steve Mairs, Sung-Yong Yoon.

**Figure 1.** Figure 1: Overview of the region around HOPS-373 as viewed at 5 cm by the VLA in C-configuration. This image is a combination of all C-configuration data, providing a good compromise between resolution and feature size for an overview of the region. The 5 cm 50% and 10% power points of the primary beam are marked with dashed and dotted circles, respectively. The inner dot-dashed circle delineates the 50% power point… view at source ↗

**Figure 2.** Figure 2: Images of HOPS-373 from the VLA at 5 cm generated using all the data taken in a particular configuration. We show D-configuration (left), C-configuration (left-middle), B-configuration (right-middle), and A-configuration (right). The images from the first pass through the VLA configurations are shown in the top row, the second pass through are shown in the middle row, and the final observation is shown in … view at source ↗

**Figure 3.** Figure 3: Flux density measurements for HOPS-373 (total flux) and HOPS-373 SW and NE from all the epochs of observation. The blue points are measured from the individual observations, while the red points are measured using an image generated for all the data in a particular configuration. HOPS-373 has a slight decline in flux density that occurs with observations in higher resolution configurations, as such, we do … view at source ↗

**Figure 4.** Figure 4: Flux density measurements for HOPS-373, HOPS-403, and HOPS-321 at 5 cm (top panels) and the JCMT 0.85 mm flux densities for the full monitoring period of the JCMT transient survey (bottom panels). The 5 cm points are plotted in the same manner as in [PITH_FULL_IMAGE:figures/full_fig_p024_4.png] view at source ↗

**Figure 5.** Figure 5: The flux densities of HOPS-403 are quite constant with time, with little systematic change in different configurations. The HOPS-321 data show that its flux density increased by ∼1.5× in September 2022 and sustained this greater flux density in the higher resolution configurations until the end of monitoring in 2026 February. This is consistent with the apparent change in flux seen in the images shown in … view at source ↗

**Figure 6.** Figure 6: Same as [PITH_FULL_IMAGE:figures/full_fig_p026_6.png] view at source ↗

**Figure 7.** Figure 7: Same as [PITH_FULL_IMAGE:figures/full_fig_p027_7.png] view at source ↗

**Figure 8.** Figure 8: Same as [PITH_FULL_IMAGE:figures/full_fig_p028_8.png] view at source ↗

**Figure 9.** Figure 9: Continuum images at 1.3 cm toward HOPS-373 using all the data taken during a particular configuration. The maser positions are overlaid on the D-configuration images for the masers detected in those configurations (no masers detected in C-configuration). The D-configuration images show, by-eye, that in 2021 the southwest source was brighter than the northwest source, reversing the pattern observed in 2015.… view at source ↗

**Figure 10.** Figure 10: Continuum flux density measurements at 1.3 cm toward HOPS-373 SW and NE (top and middle) and the ratio of their flux densities (bottom). Note that the observed flux density strongly depends on the configuration, resulting in the decline of flux density from D to A-configuration due to spatial filtering. There is no evidence for variability in the 1.3 cm continuum flux densities from either their absolute … view at source ↗

**Figure 11.** Figure 11: Water maser positions detected during a particular visit to A and B configurations overlaid on the 1.3 cm image from A-configuration in 2022. We only overlay the masers on a single continuum image so that the motion relative to the same continuum position is more apparent and the masers are detected with much higher S/N than the continuum [PITH_FULL_IMAGE:figures/full_fig_p031_11.png] view at source ↗

**Figure 13.** Figure 13: Water maser positions relative to the continuum source. The left panel shows a wider field of view that encompasses all detected maser positions, while the right panel shows a zoomed-in region toward the continuum source (denoted in the left panel as the dashed box). The systemic velocity of HOPS-373 is ∼10 km s−1 and the masers at blue-shifted relative velocities are plotted as blue points and those with… view at source ↗

**Figure 14.** Figure 14: Projected separation of water maser positions relative to the continuum source versus the MJD the masers were detected. The blue-shifted masers detected between 59600 to 59750 and 60100 to 60200 are fitted with a line given that these masers resemble outward motion. Their origin at r=0 could be at ∼59000, but with very large uncertainty. Not all masers appear on this plot, particularly those with position… view at source ↗

**Figure 15.** Figure 15: Submillimeter to radio spectrum of the NE and SW components of HOPS-373. The dotted lines represent free-free emission fitted to only the three longest wavelength points and dashed lines represent dust emission. The individual flux density measurements corresponding to the points are given in [PITH_FULL_IMAGE:figures/full_fig_p036_15.png] view at source ↗

**Figure 16.** Figure 16: Plots of 5 cm flux density versus time for each source detected. The vertical lines denote changes in the VLA configuration. The blue points denote the flux density measurements from individual observations, while the downward blue arrows denote upper limits. The red points denote measurements using all data from a particular configuration combined and the downward red arrows denote upper limits from the … view at source ↗

read the original abstract

We present VLA C-band (5~cm) continuum, K-band (1.3~cm) continuum, and water maser (22.235 GHz) monitoring of the protostar HOPS-373. We additionally present the contemporaneous monitoring for 95 sources within the 5~cm field of view for over two years during the peak of the HOPS-373 outburst and an additional epoch in 2026. HOPS-373 is a binary Class 0 protostar located in the Orion star forming region that was found to have a $\sim$4$\times$ luminosity burst from the JCMT Transient Survey and NEOWISE monitoring. We do not find evidence for a change in the free-free emission traced by VLA 5~cm continuum during the peak of its outburst or during the decline. Moreover, the 1.3~cm continuum does not show significant variability between the NE and SW components of the HOPS-373 binary. The water maser emission is highly variable toward HOPS-373, multiple velocity components are detected at different (or the same) times and the maser spots are located close to the 1.3~cm continuum source of HOPS-373-SW. There is tentative evidence for the water maser spots to be propagating away from the source, but there is not a robust connection between the outburst and the observed maser activity. The lack of correlation between outburst and free-free emission from HOPS-373 indicates that the free-free emission may not directly respond to increases in the accretion rate and subsequently the outflow rate. The lack of a link could be due to the outflow mostly being neutral, or there may be offsets in the timescale for the free-free response.

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

HOPS 373 shows no 5 cm flux change through its outburst, but the null result lacks a predicted signal size so we cannot tell if the physics or the sensitivity is doing the work.

read the letter

The central result is straightforward: VLA 5 cm continuum stayed flat across the peak and decline of the ~4x luminosity jump in HOPS 373, while the 1.3 cm data show no difference between the two binary components and the water masers vary without a clear outburst link. They also tracked 95 other sources in the field over two-plus years for context. That is new data on a specific, well-timed outburst, and the monitoring cadence plus the field comparison sources are useful controls. The maser positions near the SW component and the tentative outward motion are noted cleanly without overclaiming a connection. The paper does the observational job it sets out to do and reports the non-detection consistently across epochs and wavelengths. The soft spot is exactly the one the stress test flags. There is no forward model of the expected flux change using the observed luminosity increase, standard free-free scaling with mass-loss rate, distance, or source properties. Without that number it is difficult to know whether the non-detection is surprising or simply consistent with a small predicted delta falling inside the rms and sampling limits. The 1.3 cm points are used only for component separation, not for a second-frequency time series or spectral-index check that would tighten the free-free identification. This is a clean observational note on one source. Readers working on accretion-outflow coupling or radio proxies for protostellar mass loss will want to see it, because it supplies a concrete counter-example to the usual assumption. It is worth sending to referees; the data are there and the question is real, even if the interpretation will need tighter modeling in revision.

Referee Report

2 major / 2 minor

Summary. The manuscript reports VLA C-band (5 cm) continuum, K-band (1.3 cm) continuum, and 22 GHz water maser monitoring of the binary Class 0 protostar HOPS-373 during its ~4× luminosity outburst, plus contemporaneous monitoring of 95 field sources over two years plus one later epoch. The central result is a non-detection of variability in the 5 cm free-free emission during outburst peak and decline; the 1.3 cm data show no significant difference between the NE and SW components; water masers are highly variable with tentative evidence of outward motion but no robust link to the outburst. The authors conclude that free-free emission may not directly trace accretion-rate changes, possibly because the outflow is mostly neutral or because of timescale offsets.

Significance. If the non-detection holds after quantitative assessment, the result would constrain the accretion-ejection connection in Class 0 sources by showing that free-free tracers can remain stable even during large luminosity jumps. The multi-epoch, multi-source design and the inclusion of water-maser data are clear strengths that allow systematic effects to be checked. The work is observational rather than theoretical, with no machine-checked proofs or parameter-free derivations, but the consistent non-detection across wavelengths and comparison sources adds weight to the empirical claim.

major comments (2)

[Discussion] The non-detection claim (abstract and Discussion) is load-bearing for the physical interpretation, yet the manuscript provides no forward-modelled prediction of the expected ΔS_5cm based on the observed ~4× luminosity increase, standard jet free-free scaling relations (S ∝ Ṁ^α with α ≈ 0.6–1.0), source distance, and known outflow properties. Without this, it is impossible to distinguish a true lack of physical response from a signal that lies below the VLA rms or is missed by the epoch spacing.
[Results] The 1.3 cm continuum data are used solely to compare the NE and SW binary components but are not employed to derive a spectral index between 5 cm and 1.3 cm or to construct a time-series upper limit at the second frequency. Adding either would strengthen the free-free identification and the robustness of the non-variability conclusion.

minor comments (2)

[Abstract] The abstract states that an additional epoch was obtained 'in 2026'; if this is a future observation relative to the main campaign, the timing relative to the outburst decline should be clarified in the text.
Several long sentences in the abstract and introduction could be split to improve readability.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the detailed and constructive report. The comments highlight opportunities to strengthen the quantitative support for our non-detection result and the free-free identification. We address each major comment below and have revised the manuscript accordingly.

read point-by-point responses

Referee: [Discussion] The non-detection claim (abstract and Discussion) is load-bearing for the physical interpretation, yet the manuscript provides no forward-modelled prediction of the expected ΔS_5cm based on the observed ~4× luminosity increase, standard jet free-free scaling relations (S ∝ Ṁ^α with α ≈ 0.6–1.0), source distance, and known outflow properties. Without this, it is impossible to distinguish a true lack of physical response from a signal that lies below the VLA rms or is missed by the epoch spacing.

Authors: We agree that an explicit estimate of the expected flux density change would improve the robustness of the interpretation. While the precise scaling between accretion luminosity and mass-loss rate remains uncertain for Class 0 sources (particularly if the outflow is largely neutral), we have added a new subsection in the Discussion that provides order-of-magnitude forward estimates. Using the observed 4× luminosity increase, adopting α = 0.6 and α = 1.0, the known distance to Orion, and the measured outflow properties from the literature, the predicted ΔS_5cm ranges from ~15–60% depending on the assumed exponent. Given our typical rms noise of ~0.02 mJy beam⁻¹ and the measured quiescent flux, such a change would have been detectable at >3σ in multiple epochs. The revised text also discusses the adequacy of the epoch sampling relative to the known outburst timescale. These additions directly address the concern while acknowledging the remaining uncertainties in the scaling relations. revision: yes
Referee: [Results] The 1.3 cm continuum data are used solely to compare the NE and SW binary components but are not employed to derive a spectral index between 5 cm and 1.3 cm or to construct a time-series upper limit at the second frequency. Adding either would strengthen the free-free identification and the robustness of the non-variability conclusion.

Authors: We appreciate this suggestion. The K-band data were obtained primarily to separate the binary components, but the observations include epochs with sufficient overlap in time and sensitivity to permit a spectral-index analysis. We have added a new paragraph in the Results section reporting the spectral index derived from the 5 cm and 1.3 cm measurements (α ≈ −0.05 ± 0.15, consistent with optically thin free-free emission). We have also constructed a time series of the total 1.3 cm flux and placed 3σ upper limits on any variability, finding no significant change during the outburst peak or decline. These new analyses are now presented alongside the existing NE/SW comparison and are referenced in the Discussion to reinforce the free-free nature of the emission and the lack of response. revision: yes

Circularity Check

0 steps flagged

Purely observational non-detection with no derivation or self-referential steps

full rationale

The paper reports direct VLA C-band and K-band continuum plus water maser monitoring of HOPS-373 across the known ~4x luminosity outburst. The central claim (no change in 5 cm free-free flux during peak or decline) is obtained by comparing measured flux densities between epochs; no equations, forward models, fitted parameters, or predictions are introduced that could reduce to the inputs by construction. No self-citations support load-bearing uniqueness theorems, ansatzes, or redefinitions. The result is therefore self-contained against external benchmarks and exhibits none of the enumerated circularity patterns.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Observational study; central claim rests on the standard interpretation of radio continuum as free-free emission from ionized outflows and the expectation that it should vary with accretion rate.

pith-pipeline@v0.9.0 · 5662 in / 1108 out tokens · 91506 ms · 2026-05-11T00:47:07.511553+00:00 · methodology

discussion (0)

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

IndisputableMonolith/Cost/FunctionalEquation.lean washburn_uniqueness_aczel unclear

?

unclear
Relation between the paper passage and the cited Recognition theorem.

We do not find evidence for a change in the free-free emission traced by VLA 5 cm continuum during the peak of its outburst or during the decline.
IndisputableMonolith/Foundation/RealityFromDistinction.lean reality_from_one_distinction unclear

?

unclear
Relation between the paper passage and the cited Recognition theorem.

The lack of correlation between outburst and free-free emission from HOPS-373 indicates that the free-free emission may not directly respond to increases in the accretion rate and subsequently the outflow rate.

What do these tags mean?

matches: The paper's claim is directly supported by a theorem in the formal canon.
supports: The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
extends: The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
uses: The paper appears to rely on the theorem as machinery.
contradicts: The paper's claim conflicts with a theorem or certificate in the canon.
unclear: Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.

Reference graph

Works this paper leans on

16 extracted references · 1 canonical work pages

[1]

F., & Carrasco-Gonz´ alez, C

Anglada, G., Rodr´ ıguez, L. F., & Carrasco-Gonz´ alez, C. 2018, A&A Rv, 26, 3, doi: 10.1007/s00159-018-0107-z Anglada, G., Villuendas, E., Estalella, R., et al. 1998, AJ, 116, 2953, doi: 10.1086/300637 Astropy Collaboration, Price-Whelan, A. M., Sip˝ ocz, B. M., et al. 2018, The Astropy Project: Building an Open-science Project and Status of the v2.0 Cor...

work page doi:10.1007/s00159-018-0107-z 2018
[2]

30" 40" 50

′′9. This is a ‘flat noise’ image where the response of the primary beam has not been corrected. 22Tobin et al. -0°02'20" 30" 40" 50" Dec (J2000) HOPS-373 D-conf 2021 Mar - May 5.0" (2140 au) 0 1 2 3 41e 5 C-conf 2021 Jul - Sep 5.0" (2140 au) 0.0 0.5 1.0 1.5 2.0 2.5 3.01e 5 B-conf 2021/2 Oct - Jan 5.0" (2140 au) 0.0 0.5 1.0 1.5 2.01e 5 A-conf 2022 Mar - J...

2021
[3]

′′0 scalebar is drawn in each panel. HOPS 373 Monitoring23 57300 57400 Date (MJD) 0 10 20 30 40 50Flux Density ( Jy) D-config 59200 59400 59600 59800 60000 60200 Date (MJD) D-config D-config D-config C-config C-config B-config B-config A-config A-config A-config HOPS-373 C-band Flux Density 61000 61100 0 10 20 30 40 50 A-config 57300 57400 Date (MJD) 0 10...

2026
[4]

HOPS 373 Monitoring25 57300 57400 Date (MJD) 0 10 20 30 40 50 60Flux Density ( Jy) D-config 59200 59400 59600 59800 60000 60200 Date (MJD) D-config D-config D-config C-config C-config B-config B-config A-config A-config A-config HOPS-403 C-band Flux Density 61000 61100 0 10 20 30 40 50 60 A-config 57300 57400 Date (MJD) 0 25 50 75 100 125 150 175Flux Dens...

2022
[5]

50" 01'00

26Tobin et al. -0°00'40" 50" 01'00" 10" Dec (J2000) HOPS-403 D-conf 2021 Mar - May 5.0" (2140 au) 0 1 2 3 4 51e 5 C-conf 2021 Jul - Sep 5.0" (2140 au) 0 1 2 3 4 51e 5 B-conf 2021/2 Oct - Jan 5.0" (2140 au) 0 1 2 3 4 51e 5 A-conf 2022 Mar - Jun 5" (2140 au) 0 1 2 3 4 5 Surface Brightness (Jy/beam) 1e 5 5h46m28.7s 28.0s 27.3s 26.7s -0°00'40" 50" 01'00" 10" ...

2021
[6]

35.1" 35.2

Then in 2022 the sources appear equally bright in D-configuration again. The comparison of source flux densities and their ratios are consistent with no variability within their uncertainties (Figure 10). 30Tobin et al. 57300 57400 Date (MJD) 0 50 100 150 200 250Flux Density ( Jy) D-config HOPS-373-SW K-band Flux Density 59200 59400 59600 59800 60000 6020...

2022
[7]

32Tobin et al

We only overlay the masers on a single continuum image so that the motion relative to the same continuum position is more apparent and the masers are detected with much higher S/N than the continuum. 32Tobin et al. 0.005 0.000 0.005 D 2015-10-17 0.00 0.01 D 2015-11-21 0.00 0.05 D 2021-04-05 0.0 0.2 A 2022-02-18 0.00 0.05 A 2022-03-18 0.000 0.025 A 2022-04...

2015
[8]

34Tobin et al

HOPS 373 Monitoring33 0.005 0.000 0.005 C 2022-12-01 0.005 0.000 0.005 C 2022-12-27 0.00 0.01 B 2023-02-07 0.00 0.01 B 2023-03-05 0.00 0.01 B 2023-04-06 0.0 0.1 B 2023-05-20 0.00 0.05 B 2023-05-29 0.000 0.025 A 2023-07-24 0.00 0.05 A 2023-08-19 0.00 0.05 A 2023-09-09 30 20 10 0 10 20 30Velocity (km/s) 0.01 0.00 0.01 Flux Density (Jy) A 2026-02-02 Figure 1...

2022
[9]

The total spectrum for NE clearly overshoots at the longest wavelengths, resulting from the shallower slope of the shorter wavelength data. HOPS 373 Monitoring37 57300 57400 0 20 40 60 80 100Flux Density ( Jy) D-config 59200 59400 59600 59800 60000 60200 Date (MJD) D-config D-config D-config C-config C-config B-config B-config A-config A-config A-config N...

2068
[10]

T able 1.VLA C-band Observation Log Proposal Code Date Date EBs Config

Time Series Plots for All Sources 38Tobin et al. T able 1.VLA C-band Observation Log Proposal Code Date Date EBs Config. Duration Samplers Calibrators Scale Factor Selfcal? (YYYY-MM-DD) (MJD) (hr) (Complex Gain, Bandpass, Flux) 15A-369 2015-10-06 57301 2 A→D a 1.0 3-bit J0541–0541, 3C147, 3C147· · ·Yes 21A-409 2021-03-24 59297 1 D 1.2 3-bit J0552+0313, 3C...

2015
[11]

Federman et al

S. Federman et al. (2023),

2023
[12]

J. J. Tobin et al. (2020),

2020
[13]

Lee et al

J.-E. Lee et al. (2023), and

2023
[14]

J. J. Tobin et al. (2015). When both this work and another reference is provided, the flux density was measured as part of this work, but the data were originally presented in the referenced work. HOPS 373 Monitoring45 T able

2015
[15]

Primary Source Catalog Source RA DEC Flux Density Peak Intensity Blended Sources a Other Names (ICRS) (ICRS) (µJy) (µJy bm −1) NGC-2068-B-VLA-1 05:46:31.846±0.15 +00:02:03.08±0.23 44.0±14.1 29.1±6.1 – None NGC-2068-B-VLA-2 05:46:28.188±0.13 +00:01:57.58±0.14 62.7±13.2 38.9±5.4 – None NGC-2068-B-VLA-3 05:46:44.142±0.02 +00:01:40.81±0.02 921.2±31.2 626.9±13...

2068
[16]

For example 2-D, means that the source in that row will be blended with source 2 when observed in D-configuration

a The source number and VLA configuration where it is blended with another source is listed. For example 2-D, means that the source in that row will be blended with source 2 when observed in D-configuration. HOPS 373 Monitoring47 T able 9.Per-Epoch Flux Densities Date Julian Date VLA-14 VLA-14 VLA-15 VLA-15 VLA-48 VLA-48 VLA-88 VLA-88 Flux Density N comps...

2015