Pith. sign in

REVIEW 3 major objections 5 minor 117 references

Among megamaser disk AGN, only NGC 4258 offers a black hole shadow resolvable with Earth–L2 space VLBI baselines, and its spin-offset test is blocked by 22 GHz maser astrometry precision.

Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →

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

T0 review · deepseek-v4-flash

2026-08-03 12:42 UTC pith:OGKHLR64

load-bearing objection Useful, honest feasibility study; the geometry is solid, but the flux-based detectability conclusions rest on an unverified compactness assumption the authors themselves flag. the 3 major comments →

arxiv 2601.01763 v3 pith:OGKHLR64 submitted 2026-01-05 astro-ph.GA astro-ph.IM

When the Shadow Meets Its Measure: Assessing the Feasibility of Submillimeter Black Hole Shadow Imaging in Megamaser Disk AGN

Roman N. Burridge , Geoffrey C. Bower This is my paper
classification astro-ph.GA astro-ph.IM
keywords megamaser disk AGNblack hole shadowspace VLBIsubmillimeter continuumNGC 4258water maser astrometryadvection-dominated accretion flowvery long baseline interferometry
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

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

Water megamaser disks around supermassive black holes provide the most precise geometric anchors—mass, distance, inclination, and dynamical center—available for AGN, making them natural candidates for black hole shadow imaging once space-based very long baseline interferometry exists. The paper tests this idea for the 21 best-measured megamaser disk AGN by combining predicted shadow sizes with 200–400 GHz core flux measurements (new and archival), contamination estimates, and variability bounds. Its central conclusion is that NGC 4258 is the only source resolvable on Earth–L2 baselines, with a 0.617 microarcsecond shadow and roughly 7 mJy beam^-1 core flux; all other sample members need baselines approaching Earth–L4/L5, and only a handful exceed 10 mJy. The paper also argues that a submillimeter excess in NGC 4258 indicates the disk stays thin to within ~100 Schwarzschild radii before turning into an advection-dominated flow, and that the spin-dependent shadow offset—0.09 microarcseconds at maximal spin—is currently out of reach because the 22 GHz water maser dynamical center would need astrometry about 55 times more precise than today's measurements.

Core claim

On its own terms, the paper establishes a feasibility ranking: NGC 4258 is the only megamaser disk AGN whose predicted shadow (0.617 ± 0.049 microarcseconds) is resolved by an Earth–L2 baseline and whose ~7 mJy beam^-1 core at 230 GHz is detectable; the next-largest targets (NGC 1194, NGC 1068) need baselines about 1.4–1.6× Earth–L2, and most of the 21-source sample needs Earth–L4/L5. It further finds a submillimeter excess in NGC 4258, bounded against dust and jet contamination, which it interprets as a thin disk persisting to ≲100 Schwarzschild radii with an advection-dominated flow inside. The third result is that the spin-dependent offset between the shadow and the maser dynamical center

What carries the argument

The machinery that carries the argument is a bridge from water-maser geometry to an observing program: a 21-galaxy sample whose 22 GHz masers pin down mass, distance, inclination, and dynamical center; the shadow formula θ_BHS = sqrt(27) R_S / D; the diffraction limit θ_VLBI = λ/D_BL for Earth-diameter, Earth–Moon, Earth–L2, and Earth–L4/L5 baselines; 200–400 GHz continuum fluxes with dust (α=+4.5) and jet (α=−0.5) extrapolations bounding contamination; and the astrometric relation σ_θ ∝ θ_VLBI/SNR paired with the maximal Kerr shadow offset ≈0.725 R_S (≈0.14 θ_BHS). The last element isolates the bottleneck: the 22 GHz dynamical center must be located ~55 times more precisely than today.

Load-bearing premise

The load-bearing premise is that the arcsecond-resolution 200–400 GHz continuum measurements trace the AGN core rather than extended emission—a compactness check the paper explicitly did not perform (Sec 2.4, 5)—so if a large share of the measured flux is dust or jet emission, the detectability rankings, the ~7–10 mJy flux levels, and the submillimeter-excess/ADAF interpretation all weaken.

What would settle it

Measure NGC 4258 at ~230 GHz with the finest resolution available (a space-ground VLBI baseline, or a phased ground array with sub-milliarcsecond resolution) and compare the compact core flux with the ~7 mJy beam^-1 value measured at arcsecond resolution; if the resolved core is well below ~1 mJy, the claimed detectability and ADAF excess are unsupported. Alternatively, a multi-epoch monitoring campaign at matched beam sizes would test whether the apparent submillimeter excess is intrinsic or an artifact of variability and resolution mismatch.

Watch this falsifier. Get emailed when new claim-graph text bears on it.

Share X Bluesky LinkedIn Reddit HN

If this is right

  • NGC 4258 is the only known megamaser disk AGN whose black hole shadow could be resolved with an Earth–L2 space-ground baseline; proposed missions at that baseline would be the natural first attempt.
  • All other megamaser disk AGN in the sample—including NGC 1194 and NGC 1068, the next-largest shadows—require baselines beyond Earth–L2, approaching Earth–L4/L5, so they are out of reach for the near-term space VLBI concepts considered.
  • Only a handful of sources (NGC 3079, NGC 4945, Circinus, NGC 1068) have 230 GHz core fluxes ≳10 mJy, so sensitivity is not the sole gate; angular size is the dominant selection criterion.
  • The measured submillimeter excess in NGC 4258, with thermal-dust and jet contamination bounded low, supports a thin disk that survives to ≲100 Schwarzschild radii before transitioning to an advection-dominated flow—and implies the ADAF turnover frequency lies above 22 GHz.
  • Detecting spin through the shadow–dynamical-center offset is formally possible with an Earth–Moon baseline at 230 GHz (SNR ≈ 3.6), but requires ~55× better 22 GHz maser dynamical-center astrometry than current measurements; without that, the spin measurement is infeasible.

Where Pith is reading between the lines

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

  • Because the paper leaves compactness untested at 200–400 GHz (it says so in Sec 2.4 and Sec 5), a high-resolution follow-up that resolves the NGC 4258 core at ~230 GHz would either confirm the ~7 mJy compact flux or invalidate the detectability and ADAF claims; this is the cheapest decisive experiment.
  • The same shadow-size-versus-flux ranking could be applied to non-megamaser AGN with any precise dynamical-center tracer, turning this into a general target-selection template for space VLBI; the paper's method, not just its sample, is reusable.
  • If submillimeter water maser transitions (183, 321, 439 GHz) are found in NGC 4258—which has not yet been searched—the cross-band 22-to-230 GHz registration problem disappears, and the spin-offset measurement becomes much more tractable than the 55× astrometry gain implied here.

Editorial analysis

A structured set of objections, weighed in public.

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

Referee Report

3 major / 5 minor

Summary. The paper assesses whether water megamaser disk AGN are viable targets for black hole shadow imaging with future space VLBI. Using published mass/distance/inclination measurements for 21 sources, new SMA observations, and archival ALMA/VLA data, it computes expected BHS angular sizes, estimates 230 GHz core flux densities with thermal-dust and extended-jet contamination bounds and variability systematics, and evaluates the astrometric precision needed to detect a spin-dependent BHS offset for NGC 4258. The main claims are that NGC 4258 is the only megamaser disk AGN resolvable on Earth-L2 baselines, that only a handful of sources have S230 ≳ 10 mJy/beam, and that the spin-offset measurement is currently limited by 22 GHz maser dynamical-center astrometry, not by BHS centroid precision.

Significance. If the flux estimates hold, this is a valuable target-selection reference for next-decade space VLBI missions: it combines a homogeneous Gaussian-fitting pipeline, new SMA observations, machine-readable continuum and variability tables, and an explicit astrometric-error budget for the spin-offset observable. The angular resolvability ranking follows directly from independently measured masses/distances and the diffraction limit, so the conclusion that NGC 4258 is by far the most favorable target in angular size is robust. The spin-offset argument is well posed and shows convincingly that maser dynamical-center astrometry, not BHS centroid noise, is the bottleneck. However, the flux-based detectability conclusions rest on an untested compactness assumption that the paper itself flags, and this must be resolved or reframed before the central claims can be accepted.

major comments (3)
  1. [§2.4, §5, Tables 5–10] The fluxes used as 'AGN-core' measurements are peak fluxes from Gaussians fixed to the synthesized beam at 3–6 arcsec resolution (e.g., NGC 4258: 6.9±1.1 mJy/beam in a 3.32 arcsec beam, Table 5). Such data do not distinguish a compact core from extended dust or jet/kpc-scale emission, and the paper explicitly states that a compactness analysis has not been performed and is 'an aspect neglected in this paper' (§5; see also the degeneracy between variability and compactness in §2.4). Because the detectability thresholds in Fig. 1 and the 'only NGC 4258 detectable on Earth-L2 baselines' claim require S230 to be core flux, this is load-bearing. Please either add a compactness analysis (e.g., uv-modeling, high-resolution archival data) or re-label these as upper limits and make the NGC 4258 detectability and ADAF statements explicitly conditional.
  2. [Table 1 and §4.1] The two SMA spectral indices of NGC 4258, α=4.7±1.4 and α=1.1±1.6, are mutually inconsistent—the text itself calls the discrepancy 'difficult to explain using any plausible physical mechanism'—yet the paper adopts α=2.9±2.1 and uses this average to support the submm-excess/ADAF interpretation. Averaging two discrepant values does not produce a reliable spectral index. The claimed thin-disk-to-ADAF transition should be presented as tentative pending additional SMA epochs, or the analysis should quantify the systematic origin of the discrepancy rather than simply combining the two measurements.
  3. [§3.4] In the Rayleigh-Jeans limit of the modified blackbody Sν=Aν^{β+3}/(e^{hν/kT}-1), with β=1.5 and T≳2000 K, the spectral index is α=β+2=3.5, not α=4.5; the quoted 4.5 appears to omit the factor ν in the Planck denominator. Using α=4.5 biases the thermal-dust upper limits low by roughly 30–40% over the frequency offsets used. Please correct the model and recompute the dust extrapolation entries in Tables 5–10. The changes are likely small for the currently listed sources, but the method as stated is incorrect.
minor comments (5)
  1. [Abstract vs §3.3/§6] The abstract says the required maser dynamical-center improvement is 'roughly seventy times,' while §3.3 and §6 state a factor of '~55' (5 µas / 0.09 µas ≈ 56). Please harmonize these numbers.
  2. [Table 2 note] The table note says '20 best known SMBH-Hosting Galaxies' while the text says 21; the table lists 21 megamaser systems plus Sgr A* and M87*. Correct the caption and note.
  3. [Table 4] The machine-readable variability table contains invalid dates such as 2017/06/31 and 1998/02/31. Correct or clarify these entries.
  4. [Figure 1 caption] The caption reads '• symbols represent detections, and ▼ symbols represent upper limits. • symbols represent M87, Sgr A* for comparison.' The second sentence is redundant/confusing and should be cleaned up.
  5. [§3.5] The variability-pair selection thresholds (1.4% frequency, 2.6% beam size) are described as 'chosen empirically.' Please state the optimization criterion or provide a sensitivity test showing that the derived variability upper bounds do not depend strongly on the precise thresholds.

Circularity Check

0 steps flagged

No material circularity: BHS sizes, fluxes, and spin-offset feasibility use independent measurements and external theory; the self-flagged compactness caveat is a correctness risk, not a circular reduction.

full rationale

Walking the derivation chain: (1) BHS angular diameters come from Eq. 1 using published masses and distances (Greene et al. 2016; Pesce et al. 2018/2020; Reid et al. 2019); (2) baseline resolutions come from Eq. 2 and VLBI sensitivity from Eq. 3 with external SEFD/bandwidth parameters; (3) source flux densities are new SMA and archival ALMA/VLA Gaussian-fit measurements, not model predictions recycled into the feasibility claims; (4) the spin-offset requirement uses the theoretical 0.725 R_S offset (Takahashi 2004; Bronzwaer et al. 2020), the astrometric error relation of Reid et al. 1988, and the maser-center precision of Reid et al. 2019. The ~55x needed gain in maser astrometry is arithmetic from these independent inputs, not an identity. The paper explicitly flags the compactness of the arcsecond-scale fluxes as untested: Sec. 2.4 states 'a compactness analysis would need to be conducted; however, the sparse sampling of time and beam-size in our dataset introduces degeneracy between variability and compactness,' and Sec. 5 lists compactness as 'an aspect neglected in this paper.' This is a genuine threat to the flux-based conclusions if extended emission dominates, but it is an assumption about what was measured, not a circular reduction of a prediction to its inputs. Similarly, the internally inconsistent spectral indices for NGC 4258 (Table 1: alpha=4.7 +/- 1.4 vs 1.1 +/- 1.6) weaken the ADAF interpretation but are data-quality concerns, not circularity. The only self-citations (Burt et al. 2025; Burridge 2026) are peripheral; the coherence-time claim is corroborated by demonstrated 7-s integrations and independent Millimetron assumptions. Overall: self-contained against external benchmarks; no fitted parameter is renamed as a prediction; score 1 reflects only a minor, non-load-bearing self-citation.

Axiom & Free-Parameter Ledger

4 free parameters · 6 axioms · 0 invented entities

The central claims are observational and geometric. Shadow sizes use literature masses/distances; flux rankings use new SMA/ALMA/VLA measurements plus assumed spectral slopes for contamination. No new particles, forces, or physical entities are introduced. Free parameters are the hand-set spectral indices and variability pair-selection thresholds, which affect contamination and systematic corrections.

free parameters (4)
  • thermal dust spectral index α_dust = +4.5 (assumed)
    Used for high-frequency dust contamination extrapolation (Sec 3.4); chosen as a warm 2000 K optically thin modified-blackbody slope, not fitted to these data.
  • extended-jet spectral index α_jet = −0.5 (assumed)
    Used to project low-frequency fluxes to ν0 as upper limits on jet contamination (Sec 3.4).
  • optically thick AGN spectral index α_AGN = +2.5 (assumed)
    Used for variability systematic corrections in the submm-mm regime (Sec 3.5).
  • variability pair-selection thresholds = 1.4% frequency, 2.6% beam-size
    Chosen empirically to maximize pair counts while minimizing spectral/spatial bias (Sec 3.5); affect variability upper limits and flux uncertainties.
axioms (6)
  • standard math Schwarzschild shadow angular size θ_BHS = sqrt(27) R_S / D (Eq. 1)
    Standard GR result used to convert black hole mass and distance to predicted shadow size for all sources.
  • standard math Diffraction-limited fringe spacing θ_VLBI = λ / D_BL (Eq. 2)
    Used to compare proposed space baselines against BHS sizes.
  • standard math VLBI thermal noise and astrometric centroid uncertainty formulas (Eqs. 3–4)
    Reid et al. (1988) positional uncertainty and Walker (1995) sensitivity used for SNR and centroid-precision requirements.
  • domain assumption Water maser disk dynamical center coincides with the SMBH position and traces Keplerian rotation
    Basis for using 22 GHz maser astrometry as the reference for the BHS-maser offset; the paper notes maser spot variability, disk turbulence, and amplification geometry may bias the COM at the ~0.1 μas level (Sec 3.3).
  • domain assumption Arcsecond-scale 200–400 GHz continuum emission is dominated by the AGN core
    Needed for flux-based detectability and the NGC 4258 submm-excess interpretation; explicitly untested because compactness analysis was not performed (Sec 2.4, Sec 5).
  • domain assumption Thermal-dust contamination modeled as a 2000 K warm modified blackbody with β=1.5; jets/AGN follow α=-0.5/+2.5
    From Casey (2012), Rybicki & Lightman (1979), etc.; these slopes set the contamination upper limits in Sec 3.4–3.5.

pith-pipeline@v1.3.0-alltime-deepseek · 34640 in / 14015 out tokens · 143297 ms · 2026-08-03T12:42:52.553703+00:00 · methodology

0 comments
Cite this review

Pith. "Pith review of When the Shadow Meets Its Measure: Assessing the Feasibility of Submillimeter Black Hole Shadow Imaging in Megamaser Disk AGN." pith.science (2026). https://pith.science/paper/OGKHLR64

@misc{pith2026260101763,
  author       = {Pith},
  title        = {Pith review of: When the Shadow Meets Its Measure: Assessing the Feasibility of Submillimeter Black Hole Shadow Imaging in Megamaser Disk AGN},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/OGKHLR64}},
  note         = {Machine review of arXiv:2601.01763}
}
Share X Bluesky LinkedIn Reddit HN
read the original abstract

Active galactic nuclei (AGN) hosting water megamaser disks provide precise geometric measurements of black hole mass, distance, maser disk orientation, and dynamical center. In anticipation of space-based very long baseline interferometry, these systems offer a path to black hole shadow (BHS) imaging beyond Sgr A* and M87*. We present new Submillimeter Array continuum observations of water megamaser galaxies, supplemented by archival ALMA and VLA measurements, to assess whether their AGN cores are bright enough for BHS-scale imaging. For a 21-source parent sample, we map the predicted BHS diameters of systems with published SMBH masses to submillimeter/millimeter (submm-mm) baseline requirements, estimate AGN core flux densities at 230 GHz while bounding thermal dust and extended-jet contamination and checking whether variability could affect the continuum estimates, and evaluate the astrometric precision required to detect spin-dependent BHS offsets for NGC 4258. NGC 4258 is the only source resolvable on Earth-L2 baselines; other targets require longer baselines approaching Earth-L4/L5 distances, and only a handful have $S_{230} \gtrsim 10$ mJy beam$^{-1}$. We also find a submillimeter excess in NGC 4258, suggesting that its disk remains geometrically thin to $\lesssim 100$ Schwarzschild radii before transitioning to an advection-dominated flow. Even for maximal spin, the formal 230 GHz BHS centroid precision is not the limiting term: the measurement would require locating the 22 GHz water maser dynamical center and registering it to the 230 GHz BHS image roughly seventy times more precisely than current maser astrometry allows, making the spin-offset measurement infeasible with present data.

Figures

Figures reproduced from arXiv: 2601.01763 by Geoffrey C. Bower, Roman N. Burridge.

Figure 1
Figure 1. Figure 1: Resolution and sensitivity requirements for resolving BHS of water megamaser SMBHs using VLBI. Each point shows an approximate estimate of angular BHS size and flux density at submm-mm for a given water megamaser AGN. • symbols represent detections, and ▼ symbols represent upper limits. • symbols represent M87, Sgr A* for comparison. Vertical lines correspond to the angular resolution at 230 GHz for baseli… view at source ↗
Figure 2
Figure 2. Figure 2: Left Panel: SED of NGC 4258. Data points correspond to continuum observations from the SMA, SCUBA-JCMT, VLA, and NMA. Due to its northern declination, NGC 4258 is outside the observable range of ALMA. The inset shows the angular to linear scale, and the color bar denotes FWHM synthesized beam size. Right Panel: Variability of NGC 4258. The horizontal axis indicates the time difference between observations,… view at source ↗
Figure 3
Figure 3. Figure 3: SED of NGC 1194. Data points correspond to continuum observations from the SMA, ALMA, and VLA. The inset shows the angular to linear scale, and the color bar denotes FWHM synthesized beam size [PITH_FULL_IMAGE:figures/full_fig_p016_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Left Panel: SED of NGC 3079. Data points correspond to continuum observations from the SMA and VLA. Due to its northern declination, NGC 3079 is outside the observable range of ALMA. The inset shows the angular to linear scale, and the color bar denotes FWHM synthesized beam size. Right Panel: Variability of NGC 3079. The horizontal axis indicates the time difference between observations, while the vertica… view at source ↗
Figure 5
Figure 5. Figure 5: Left Panel: SED of NGC 4945. Data points correspond to continuum observations from ALMA. Due to its southern declination, NGC 4945 is outside the observable range of the SMA and VLA. The inset shows the angular to linear scale, and the color bar denotes FWHM synthesized beam size. Right Panel: Variability of NGC 4945. The horizontal axis indicates the time difference between observations, while the vertica… view at source ↗
Figure 6
Figure 6. Figure 6: Left Panel: SED of Circinus. Data points correspond to continuum observations from ALMA. Due to its southern declination, Circinus is outside the observable range of the SMA and VLA. The inset shows the angular to linear scale, and the color bar denotes FWHM synthesized beam size. Right Panel: Variability of Circinus. The horizontal axis indicates the time difference between observations, while the vertica… view at source ↗
Figure 7
Figure 7. Figure 7: Left Panel: SED of NGC 1068. Data points correspond to continuum observations from the SMA, ALMA, and VLA. The inset shows the angular to linear scale, and the color bar denotes FWHM synthesized beam size. Right Panel: Variability of NGC 1068. The horizontal axis indicates the time difference between observations, while the vertical axis shows the percentage difference in flux density between the two obser… view at source ↗

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Reference graph

Works this paper leans on

117 extracted references · 34 canonical work pages · 1 internal anchor

  1. [1]

    2024, in Space Telescopes and Instrumentation 2024: Optical, Infrared, and Millimeter Wave, ed

    Akiyama, K., Niinuma, K., Hada, K., et al. 2024, in Space Telescopes and Instrumentation 2024: Optical, Infrared, and Millimeter Wave, ed. L. E. Coyle, M. D. Perrin, & S. Matsuura (SPIE), 91, doi: 10.1117/12.3019968

    doi:10.1117/12.3019968 2024

  2. [2]

    D., Allende Prieto, C., Almeida, A., et al

    Albareti, F. D., Allende Prieto, C., Almeida, A., et al. 2017, ApJS, 233, 25, doi: 10.3847/1538-4365/aa8992

    doi:10.3847/1538-4365/aa8992 2017

  3. [3]

    S., Baryshev, A

    Andrianov, A. S., Baryshev, A. M., Falcke, H., et al. 2020, Monthly Notices of the Royal Astronomical Society, 500, 4866, doi: 10.1093/mnras/staa2709

    work page doi:10.1093/mnras/staa2709 2020

  4. [4]

    2024, ApJ, 964, 172, doi: 10.3847/1538-4357/ad2175 Bardeen

    Baer-Way, R., DeGraw, A., Zheng, W., et al. 2024, ApJ, 964, 172, doi: 10.3847/1538-4357/ad2175 Bardeen. 1973, Black Holes (New York: Gordon and Breach)

    doi:10.3847/1538-4357/ad2175 2024

  5. [5]

    J., Henkel, C., D’Cruze, M

    Bendo, G. J., Henkel, C., D’Cruze, M. J., et al. 2016, Monthly Notices of the Royal Astronomical Society, 463, 252, doi: 10.1093/mnras/stw1659

    doi:10.1093/mnras/stw1659 2016

  6. [6]

    D., & K¨ onigl, A

    Blandford, R. D., & K¨ onigl, A. 1979, ApJ, 232, 34, doi: 10.1086/157262

    doi:10.1086/157262 1979

  7. [7]

    D., & Ostriker, J

    Blandford, R. D., & Ostriker, J. P. 1978, ApJL, 221, L29, doi: 10.1086/182658

    doi:10.1086/182658 1978

  8. [8]

    D., Wolfire, M., & Leroy, A

    Bolatto, A. D., Wolfire, M., & Leroy, A. K. 2013, ARA&A, 51, 207, doi: 10.1146/annurev-astro-082812-140944

    doi:10.1146/annurev-astro-082812-140944 2013

  9. [9]

    C., Dexter, J., Markoff, S., et al

    Bower, G. C., Dexter, J., Markoff, S., et al. 2015, ApJL, 811, L6, doi: 10.1088/2041-8205/811/1/L6

    doi:10.1088/2041-8205/811/1/l6 2015

  10. [10]

    2011, Monthly Notices of the Royal Astronomical Society, 413, 1206, doi: 10.1111/j.1365-2966.2011.18207.x

    Brightman, M., & Nandra, K. 2011, Monthly Notices of the Royal Astronomical Society, 413, 1206, doi: 10.1111/j.1365-2966.2011.18207.x

    arXiv 2011

  11. [11]

    2020, Monthly Notices of the Royal Astronomical Society, 501, 4722, doi: 10.1093/mnras/staa3430

    Bronzwaer, T., Davelaar, J., Younsi, Z., et al. 2020, Monthly Notices of the Royal Astronomical Society, 501, 4722, doi: 10.1093/mnras/staa3430

    work page doi:10.1093/mnras/staa3430 2020

  12. [12]

    2026, RomanBurridge/Burridge2025-WM-AGN-Analysis, Zenodo, doi: 10.5281/zenodo.18135781 24

    Burridge, R. 2026, RomanBurridge/Burridge2025-WM-AGN-Analysis, Zenodo, doi: 10.5281/zenodo.18135781 24

    work page doi:10.5281/zenodo.18135781 2026

  13. [13]

    2025, Frequency Standard Contributions to Limitations on the Signal-to-Noise Ratio in Very Long Baseline Interferometric (VLBI) Observations

    Burt, E., Ely, T., Bower, G., et al. 2025, Frequency Standard Contributions to Limitations on the Signal-to-Noise Ratio in Very Long Baseline Interferometric (VLBI) Observations. https://arxiv.org/abs/2508.19123

    Pith/arXiv arXiv 2025

  14. [14]

    M., Bentz, M

    Cackett, E. M., Bentz, M. C., & Kara, E. 2021, iScience, 24, 102557, doi: 10.1016/j.isci.2021.102557

    arXiv 2021

  15. [15]

    Casey, C. M. 2012, MNRAS, 425, 3094, doi: 10.1111/j.1365-2966.2012.21455.x

    arXiv 2012

  16. [16]

    C., Dexter, J., et al

    Chen, B.-Y., Bower, G. C., Dexter, J., et al. 2023, The Astrophysical Journal, 951, 93, doi: 10.3847/1538-4357/acd250

    doi:10.3847/1538-4357/acd250 2023

  17. [17]

    2019, Science, 365, 664, doi: 10.1126/science.aav8137

    Do, T., Hees, A., Ghez, A., et al. 2019, Science, 365, 664, doi: 10.1126/science.aav8137

    doi:10.1126/science.aav8137 2019

  18. [18]

    2005, Monthly Notices of the Royal Astronomical Society, 363, 692, doi: 10.1111/j.1365-2966.2005.09471.x

    Doi, A., Kameno, S., Kohno, K., Nakanishi, K., & Inoue, M. 2005, Monthly Notices of the Royal Astronomical Society, 363, 692, doi: 10.1111/j.1365-2966.2005.09471.x

    arXiv 2005

  19. [19]

    2021, Monthly Notices of the Royal Astronomical Society, 512, 5183–5213, doi: 10.1093/mnras/stab3642

    Efstathiou, A., Farrah, D., Afonso, J., et al. 2021, Monthly Notices of the Royal Astronomical Society, 512, 5183–5213, doi: 10.1093/mnras/stab3642

    work page doi:10.1093/mnras/stab3642 2021

  20. [21]

    L., Bolatto, A

    Emig, K. L., Bolatto, A. D., Leroy, A. K., et al. 2020, The Astrophysical Journal, 903, 50, doi: 10.3847/1538-4357/abb67d Event Horizon Telescope Collaboration, Akiyama, K.,

    doi:10.3847/1538-4357/abb67d 2020

  21. [22]

    2019b, The Astrophysical Journal Letters, 875, L2, doi: 10.3847/2041-8213/ab0c96 —

    Alberdi, A., et al. 2019b, The Astrophysical Journal Letters, 875, L2, doi: 10.3847/2041-8213/ab0c96 —. 2019f, The Astrophysical Journal Letters, 875, L6, doi: 10.3847/2041-8213/ab1141 —. 2021b, ApJL, 910, L13, doi: 10.3847/2041-8213/abe4de —. 2022d, The Astrophysical Journal Letters, 930, L15, doi: 10.3847/2041-8213/ac6736 —. 2022e, The Astrophysical Jou...

    doi:10.3847/2041-8213/ab0c96 2041

  22. [23]

    Fabian, A. C. 2012, ARA&A, 50, 455, doi: 10.1146/annurev-astro-081811-125521

    doi:10.1146/annurev-astro-081811-125521 2012

  23. [24]

    C., Barcons, X., Almaini, O., & Iwasawa, K

    Fabian, A. C., Barcons, X., Almaini, O., & Iwasawa, K. 1998, Monthly Notices of the Royal Astronomical Society, 297, L11, doi: 10.1046/j.1365-8711.1998.01645.x

    arXiv 1998

  24. [25]

    C., Johnson, M

    Fischer, T. C., Johnson, M. C., Secrest, N. J., Crenshaw, D. M., & Kraemer, S. B. 2023, The Astrophysical Journal, 953, 87, doi: 10.3847/1538-4357/ace1f0

    doi:10.3847/1538-4357/ace1f0 2023

  25. [26]

    F., Baum, S

    Gallimore, J. F., Baum, S. A., & O’Dea, C. P. 2004, ApJ, 613, 794, doi: 10.1086/423167

    doi:10.1086/423167 2004

  26. [27]

    F., & Impellizzeri, C

    Gallimore, J. F., & Impellizzeri, C. M. V. 2023, The Astrophysical Journal, 951, 109, doi: 10.3847/1538-4357/acd846

    work page doi:10.3847/1538-4357/acd846 2023

  27. [28]

    F., Impellizzeri, C

    Gallimore, J. F., Impellizzeri, C. M. V., Aghelpasand, S., et al. 2024, The Discovery of Polarized Water Vapor Megamaser Emission in a Molecular Accretion Disk. https://arxiv.org/abs/2410.10569

    Pith/arXiv arXiv 2024

  28. [29]

    A., Reid, M

    Gao, F., Braatz, J. A., Reid, M. J., et al. 2016b, The Astrophysical Journal, 834, 52, doi: 10.3847/1538-4357/834/1/52

    doi:10.3847/1538-4357/834/1/52

  29. [30]

    2011, The Astrophysical Journal, 729, 119, doi: 10.1088/0004-637X/729/2/119

    Gebhardt, K., Adams, J., Richstone, D., et al. 2011, The Astrophysical Journal, 729, 119, doi: 10.1088/0004-637X/729/2/119

    doi:10.1088/0004-637x/729/2/119 2011

  30. [31]

    2021, ARA&A, 59, 21, doi: 10.1146/annurev-astro-111720-030029

    Gezari, S. 2021, ARA&A, 59, 21, doi: 10.1146/annurev-astro-111720-030029

    doi:10.1146/annurev-astro-111720-030029 2021

  31. [32]

    K., & Michel, D

    Gliozzi, M., Williams, J. K., & Michel, D. A. 2021, Monthly Notices of the Royal Astronomical Society, 502, 3329–3342, doi: 10.1093/mnras/stab181

    work page doi:10.1093/mnras/stab181 2021

  32. [33]

    D., & Alexander, D

    Goulding, A. D., & Alexander, D. M. 2009, Monthly Notices of the Royal Astronomical Society, 398, 1165, doi: 10.1111/j.1365-2966.2009.15194.x GRA VITY Collaboration, Abuter, R., Aimar, N., et al. 2022, A&A, 657, L12, doi: 10.1051/0004-6361/202142465

    arXiv 2009

  33. [34]

    D., Baudry, A., Richards, A

    Gray, M. D., Baudry, A., Richards, A. M. S., et al. 2015, Monthly Notices of the Royal Astronomical Society, 456, 374, doi: 10.1093/mnras/stv2437

    work page doi:10.1093/mnras/stv2437 2015

  34. [35]

    E., Seth, A., Kim, M., et al

    Greene, J. E., Seth, A., Kim, M., et al. 2016, The Astrophysical Journal Letters, 826, L32, doi: 10.3847/2041-8205/826/2/L32

    doi:10.3847/2041-8205/826/2/l32 2016

  35. [36]

    J., Gwinn, C

    Greenhill, L. J., Gwinn, C. R., Antonucci, R., & Barvainis, R. 1996, The Astrophysical Journal, 472, L21, doi: 10.1086/310346

    doi:10.1086/310346 1996

  36. [37]

    J., Moran, J

    Greenhill, L. J., Moran, J. M., & Herrnstein, J. R. 1997, ApJL, 481, L23, doi: 10.1086/310643

    work page doi:10.1086/310643 1997

  37. [38]

    J., Booth, R

    Greenhill, L. J., Booth, R. S., Ellingsen, S. P., et al. 2003, ApJ, 590, 162, doi: 10.1086/374862

    doi:10.1086/374862 2003

  38. [39]

    Hagiwara, Y., Horiuchi, S., Imanishi, M., & Edwards, P. G. 2021, The Astrophysical Journal, 923, 251, doi: 10.3847/1538-4357/ac3089

    work page doi:10.3847/1538-4357/ac3089 2021

  39. [40]

    M., & Best, P

    Heckman, T. M., & Best, P. N. 2014, ARA&A, 52, 589, doi: 10.1146/annurev-astro-081913-035722

    doi:10.1146/annurev-astro-081913-035722 2014

  40. [41]

    R., Greenhill, L

    Herrnstein, J. R., Greenhill, L. J., Moran, J. M., et al. 1998b, The Astrophysical Journal, 497, L69, doi: 10.1086/311284

    work page doi:10.1086/311284

  41. [42]

    R., Moran, J

    Herrnstein, J. R., Moran, J. M., Greenhill, L. J., & Trotter, A. S. 2005, ApJ, 629, 719, doi: 10.1086/431421 25

    doi:10.1086/431421 2005

  42. [43]

    2025, Lunar Orbital VLBI Experiment: motivation, scientific purposes and status

    Hong, X., Wu, W., Liu, Q., et al. 2025, Lunar Orbital VLBI Experiment: motivation, scientific purposes and status. https://arxiv.org/abs/2507.16317

    arXiv 2025

  43. [44]

    2007, Astronomy & Astrophysics, 469, 899–912, doi: 10.1051/0004-6361:20077529

    Hovatta, T., Tornikoski, M., Lainela, M., et al. 2007, Astronomy & Astrophysics, 469, 899–912, doi: 10.1051/0004-6361:20077529

    doi:10.1051/0004-6361:20077529 2007

  44. [45]

    P., Vogeley, M

    Huchra, J. P., Vogeley, M. S., & Geller, M. J. 1999, ApJS, 121, 287, doi: 10.1086/313194

    doi:10.1086/313194 1999

  45. [46]

    Humphreys, E. M. L., Greenhill, L. J., Reid, M. J., et al. 2005, ApJL, 634, L133, doi: 10.1086/498890

    work page doi:10.1086/498890 2005

  46. [47]

    Humphreys, E. M. L., Reid, M. J., Greenhill, L. J., Moran, J. M., & Argon, A. L. 2008, ApJ, 672, 800, doi: 10.1086/523637

    doi:10.1086/523637 2008

  47. [48]

    Humphreys, E. M. L., Vlemmings, W. H. T., Impellizzeri, C. M. V., et al. 2016, Astronomy & Astrophysics, 592, L13, doi: 10.1051/0004-6361/201629168

    work page doi:10.1051/0004-6361/201629168 2016

  48. [49]

    2014, Publications of the Astronomical Society of Japan, 66, L8, doi: 10.1093/pasj/psu079

    Inoue, Y., & Doi, A. 2014, Publications of the Astronomical Society of Japan, 66, L8, doi: 10.1093/pasj/psu079

    doi:10.1093/pasj/psu079 2014

  49. [50]

    A., & Seaquist, E

    Irwin, J. A., & Seaquist, E. R. 1988, ApJ, 335, 658, doi: 10.1086/166956

    doi:10.1086/166956 1988

  50. [51]

    2024, in Space Telescopes and Instrumentation 2024: Optical, Infrared, and Millimeter Wave, ed

    Issaoun, S., Alonso, K., Akiyama, K., et al. 2024, in Space Telescopes and Instrumentation 2024: Optical, Infrared, and Millimeter Wave, ed. L. E. Coyle, M. D. Perrin, & S. Matsuura (SPIE), 193, doi: 10.1117/12.3020041

    doi:10.1117/12.3020041 2024

  51. [52]

    2022, Applications of the source-frequency phase-referencing technique for ngEHT observations

    Jiang, W., Zhao, G.-Y., Shen, Z.-Q., et al. 2022, Applications of the source-frequency phase-referencing technique for ngEHT observations. https://arxiv.org/abs/2212.08994

    Pith/arXiv arXiv 2022

  52. [53]

    2024, in Space Telescopes and Instrumentation 2024: Optical, Infrared, and Millimeter Wave, ed

    Johnson, M., Akiyama, K., Baturin, R., et al. 2024, in Space Telescopes and Instrumentation 2024: Optical, Infrared, and Millimeter Wave, ed. L. E. Coyle, M. D. Perrin, & S. Matsuura (SPIE), 90, doi: 10.1117/12.3019835

    doi:10.1117/12.3019835 2024

  53. [54]

    2017, A&A, 605, A84, doi: 10.1051/0004-6361/201730899

    Kamali, F., Henkel, C., Brunthaler, A., et al. 2017, A&A, 605, A84, doi: 10.1051/0004-6361/201730899

    work page doi:10.1051/0004-6361/201730899 2017

  54. [55]

    J., Pawlowski, M

    Kanehisa, K. J., Pawlowski, M. S., M¨ uller, O., & Sohn, S. T. 2023, MNRAS, 519, 6184, doi: 10.1093/mnras/stad061

    work page doi:10.1093/mnras/stad061 2023

  55. [56]

    I., & Pauliny-Toth, I

    Kellermann, K. I., & Pauliny-Toth, I. I. K. 1981, ARA&A, 19, 373, doi: 10.1146/annurev.aa.19.090181.002105

    arXiv 1981

  56. [57]

    C., & Evans, N

    Kennicutt, R. C., & Evans, N. J. 2012, ARA&A, 50, 531, doi: 10.1146/annurev-astro-081811-125610

    doi:10.1146/annurev-astro-081811-125610 2012

  57. [58]

    T., Greenhill, L

    Kondratko, P. T., Greenhill, L. J., & Moran, J. M. 2005, ApJ, 618, 618, doi: 10.1086/426101

    doi:10.1086/426101 2005

  58. [59]

    Kormendy, J., & Ho, L. C. 2013, ARA&A, 51, 511, doi: 10.1146/annurev-astro-082708-101811

    doi:10.1146/annurev-astro-082708-101811 2013

  59. [60]

    J., Trakhtenbrot, B., Ricci, C., et al

    Koss, M. J., Trakhtenbrot, B., Ricci, C., et al. 2022, ApJS, 261, 6, doi: 10.3847/1538-4365/ac650b

    doi:10.3847/1538-4365/ac650b 2022

  60. [61]

    2006, A&A, 446, 113, doi: 10.1051/0004-6361:20053729

    Krips, M., Eckart, A., Neri, R., et al. 2006, A&A, 446, 113, doi: 10.1051/0004-6361:20053729

    work page doi:10.1051/0004-6361:20053729 2006

  61. [62]

    Y., Braatz, J

    Kuo, C. Y., Braatz, J. A., Condon, J. J., et al. 2010, The Astrophysical Journal, 727, 20, doi: 10.1088/0004-637X/727/1/20

    doi:10.1088/0004-637x/727/1/20 2010

  62. [63]

    P., Abramowicz, M

    Lasota, J. P., Abramowicz, M. A., Chen, X., et al. 1996, ApJ, 462, 142, doi: 10.1086/177137

    work page doi:10.1086/177137 1996

  63. [64]

    Lenc, E., & Tingay, S. J. 2009, AJ, 137, 537, doi: 10.1088/0004-6256/137/1/537

    doi:10.1088/0004-6256/137/1/537 2009

  64. [65]

    R., Ma, C.-P., & Walsh, J

    Liepold, E. R., Ma, C.-P., & Walsh, J. L. 2023, The Astrophysical Journal Letters, 945, L35, doi: 10.3847/2041-8213/acbbcf

    doi:10.3847/2041-8213/acbbcf 2023

  65. [66]

    F., Rudnitskiy, A

    Likhachev, S. F., Rudnitskiy, A. G., Shchurov, M. A., et al. 2022, Monthly Notices of the Royal Astronomical Society, 511, 668–682, doi: 10.1093/mnras/stac079

    work page doi:10.1093/mnras/stac079 2022

  66. [67]

    L., Cohen, M

    Lister, M. L., Cohen, M. H., Homan, D. C., et al. 2009, AJ, 138, 1874, doi: 10.1088/0004-6256/138/6/1874

    doi:10.1088/0004-6256/138/6/1874 2009

  67. [68]

    Lo, K. Y. 2005, ARA&A, 43, 625, doi: 10.1146/annurev.astro.41.011802.094927

    Pith/arXiv arXiv 2005

  68. [69]

    1993, ApJS, 88, 383, doi: 10.1086/191826

    Lamphier, C. 1993, ApJS, 88, 383, doi: 10.1086/191826

    work page doi:10.1086/191826 1993

  69. [70]

    1997, ApJ, 477, 585, doi: 10.1086/303727

    Mahadevan, R. 1997, ApJ, 477, 585, doi: 10.1086/303727

    doi:10.1086/303727 1997

  70. [71]

    P., et al

    Marconi, A., Oliva, E., van der Werf, P. P., et al. 2000, A&A, 357, 24, doi: 10.48550/arXiv.astro-ph/0002244 Mart ´ ın, S., Mangum, J. G., Harada, N., et al. 2021, Astronomy &; Astrophysics, 656, A46, doi: 10.1051/0004-6361/202141567

    Pith/arXiv arXiv doi:10.48550/arxiv.astro-ph/0002244 2000

  71. [72]

    M., & Young, K

    Menten, K. M., & Young, K. 1995, ApJL, 450, L67, doi: 10.1086/316776

    work page doi:10.1086/316776 1995

  72. [73]

    P., Roy, A

    Middelberg, E., Krichbaum, T. P., Roy, A. L., Witzel, A., & Zensus, J. A. 2003, Approaching NGC3079 with VLBI. https://arxiv.org/abs/astro-ph/0309382

    Pith/arXiv arXiv 2003

  73. [74]

    1996, A&A, 308, L1

    Marconi, A., & Oliva, E. 1996, A&A, 308, L1

    1996

  74. [75]

    2022, Publications of the Astronomical Society of Japan, 75, 71, doi: 10.1093/pasj/psac092

    Nakai, N. 2022, Publications of the Astronomical Society of Japan, 75, 71, doi: 10.1093/pasj/psac092

    work page doi:10.1093/pasj/psac092 2022

  75. [76]

    J., Condon, J

    Murphy, E. J., Condon, J. J., Schinnerer, E., et al. 2011, ApJ, 737, 67, doi: 10.1088/0004-637X/737/2/67

    doi:10.1088/0004-637x/737/2/67 2011

  76. [77]

    M., del Palacio, S., Beswick, R

    Mutie, I. M., del Palacio, S., Beswick, R. J., et al. 2025, Monthly Notices of the Royal Astronomical Society, 539, 808, doi: 10.1093/mnras/staf524

    doi:10.1093/mnras/staf524 2025

  77. [78]

    M., Williams-Baldwin, D., Beswick, R

    Mutie, I. M., Williams-Baldwin, D., Beswick, R. J., et al. 2024, Monthly Notices of the Royal Astronomical Society, 527, 11756, doi: 10.1093/mnras/stad3864

    doi:10.1093/mnras/stad3864 2024

  78. [79]

    Muxlow, T. W. B., Pedlar, A., Holloway, A. J., Gallimore, J. F., & Antonucci, R. R. J. 1996, MNRAS, 278, 854, doi: 10.1093/mnras/278.3.854

    work page doi:10.1093/mnras/278.3.854 1996

  79. [80]

    1995, ApJ, 444, 231, doi: 10.1086/175599 26

    Narayan, R., & Yi, I. 1995, ApJ, 444, 231, doi: 10.1086/175599 26

    doi:10.1086/175599 1995

  80. [81]

    Nesterenok, A. V. 2015, Monthly Notices of the Royal Astronomical Society, 449, 2875, doi: 10.1093/mnras/stv485

    work page doi:10.1093/mnras/stv485 2015

Showing first 80 references.