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REVIEW 4 major objections 5 minor 3 cited by

A multi-frequency study of sub-parsec jets with the Event Horizon Telescope

T0 review · 4 major / 5 minor · reviewed 2026-08-10 · deepseek-v4-flash

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Pith's one-line read Combining the first 230 GHz VLBI images of 16 active galactic nuclei with archival lower-frequency data, this paper finds core brightness temperature falling as $T_\mathrm{b}\propto\nu^{-0.95}$ and concludes sub-parsec jets must…

desk verdict A useful 230 GHz core catalogue with a plausible but assumption-bound interpretation; the optically thick core hypothesis needs a quantitative check before accepting the BK-deviation conclusion. read the letter →

arxiv 2501.05518 v1 pith:GII5OEPA submitted 2025-01-09 astro-ph.HE astro-ph.GAastro-ph.IM

Jan Röder , Maciek Wielgus , Andrei P. Lobanov , Thomas P. Krichbaum , Dhanya G. Nair , Sang-Sung Lee , Eduardo Ros , Vincent L. Fish
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Lindy Blackburn Chi-kwan Chan Sara Issaoun Michael Janssen Michael D. Johnson Sheperd S. Doeleman Geoffrey C. Bower Geoffrey B. Crew Remo P. J. Tilanus Tuomas Savolainen C. M. Violette Impellizzeri Antxon Alberdi Anne-Kathrin Baczko José L. Gómez Ru-Sen Lu Georgios F. Paraschos Efthalia Traianou Ciriaco Goddi Daewon Kim Mikhail Lisakov Yuri Y. Kovalev Petr A. Voitsik Kirill V. Sokolovsky Kazunori Akiyama Ezequiel Albentosa-Ruíz Walter Alef Juan Carlos Algaba Richard Anantua Keiichi Asada Rebecca Azulay Uwe Bach David Ball Mislav Baloković Bidisha Bandyopadhyay John Barrett Michi Bauböck Bradford A. Benson Dan Bintley Raymond Blundell Katherine L. Bouman Michael Bremer Christiaan D. Brinkerink Roger Brissenden Silke Britzen Avery E. Broderick Dominique Broguiere Thomas Bronzwaer Sandra Bustamante Do-Young Byun John E. Carlstrom Chiara Ceccobello Andrew Chael Dominic O. Chang Koushik Chatterjee Shami Chatterjee Ming-Tang Chen Yongjun Chen Xiaopeng Cheng Ilje Cho Pierre Christian Nicholas S. Conroy John E. Conway James M. Cordes Thomas M. Crawford Alejandro Cruz-Osorio Yuzhu Cui Brandon Curd Rohan Dahale Jordy Davelaar Mariafelicia De Laurentis Roger Deane Jessica Dempsey Gregory Desvignes Jason Dexter Vedant Dhruv Indu K. Dihingia Sean Taylor Dougall Sergio A. Dzib Ralph P. Eatough Razieh Emami Heino Falcke Joseph Farah Edward Fomalont H. Alyson Ford Marianna Foschi Raquel Fraga-Encinas William T. Freeman Per Friberg Christian M. Fromm Antonio Fuentes Peter Galison Charles F. Gammie Roberto García Olivier Gentaz Boris Georgiev Roman Gold Arturo I. Gómez-Ruiz Minfeng Gu Mark Gurwell Kazuhiro Hada Daryl Haggard Kari Haworth Michael H. Hecht Ronald Hesper Dirk Heumann Luis C. Ho Paul Ho Mareki Honma Chih-Wei L. Huang Lei Huang David H. Hughes Shiro Ikeda Makoto Inoue David J. James Buell T. Jannuzi Britton Jeter Wu Jiang Alejandra Jiménez-Rosales Svetlana Jorstad Abhishek V. Joshi Taehyun Jung Mansour Karami Ramesh Karuppusamy Tomohisa Kawashima Garrett K. Keating Mark Kettenis Dong-Jin Kim Jae-Young Kim Jongsoo Kim Junhan Kim Motoki Kino Jun Yi Koay Prashant Kocherlakota Yutaro Kofuji Shoko Koyama Carsten Kramer Joana A. Kramer Michael Kramer Cheng-Yu Kuo Noemi La Bella Tod R. Lauer Daeyoung Lee Po Kin Leung Aviad Levis Zhiyuan Li Rocco Lico Greg Lindahl Michael Lindqvist Jun Liu Kuo Liu Elisabetta Liuzzo Wen-Ping Lo Laurent Loinard Colin J. Lonsdale Amy E. Lowitz Nicholas R. MacDonald Jirong Mao Nicola Marchili Sera Markoff Daniel P. Marrone Alan P. Marscher Iván Martí-Vidal Satoki Matsushita Lynn D. Matthews Lia Medeiros Karl M. Menten Daniel Michalik Izumi Mizuno Yosuke Mizuno James M. Moran Kotaro Moriyama Monika Moscibrodzka Wanga Mulaudzi Cornelia Müller Hendrik Müller Alejandro Mus Gibwa Musoke Ioannis Myserlis Andrew Nadolski Hiroshi Nagai Neil M. Nagar Masanori Nakamura Gopal Narayanan Iniyan Natarajan Antonios Nathanail Santiago Navarro Fuentes Joey Neilsen Roberto Neri Chunchong Ni Aristeidis Noutsos Michael A. Nowak Junghwan Oh Hiroki Okino Héctor R. Olivares Sánchez Gisela N. Ortiz-León Tomoaki Oyama Feryal özel Daniel C. M. Palumbo Jongho Park Harriet Parsons Nimesh Patel Ue-Li Pen Dominic W. Pesce Vincent Piétu Richard Plambeck Aleksandar PopStefanija Oliver Porth Felix M. Pötzl Ben Prather Jorge A. Preciado-López Giacomo Principe Dimitrios Psaltis Hung-Yi Pu Venkatessh Ramakrishnan Ramprasad Rao Mark G. Rawlings Angelo Ricarte Bart Ripperda Freek Roelofs Alan Rogers Cristina Romero-Cañizales Arash Roshanineshat Helge Rottmann Alan L. Roy Ignacio Ruiz Chet Ruszczyk Kazi L. J. Rygl Salvador Sánchez David Sánchez-Argüelles Miguel Sánchez-Portal Mahito Sasada Kaushik Satapathy F. Peter Schloerb Jonathan Schonfeld Karl-Friedrich Schuster Lijing Shao Zhiqiang Shen Des Small Bong Won Sohn Jason SooHoo León David Sosapanta Salas Kamal Souccar Joshua S. Stanway He Sun Fumie Tazaki Alexandra J. Tetarenko Paul Tiede Michael Titus Pablo Torne Teresa Toscano Tyler Trent Sascha Trippe Matthew Turk Ilse van Bemmel Huib J. van Langevelde Daniel R. van Rossum Jesse Vos Jan Wagner Derek Ward-Thompson John Wardle Jasmin E. Washington Jonathan Weintroub Robert Wharton Kaj Wiik Gunther Witzel Michael F. Wondrak George N. Wong Qingwen Wu Nitika Yadlapalli Paul Yamaguchi Aristomenis Yfantis Doosoo Yoon André Young Ken Young Ziri Younsi Wei Yu Feng Yuan Ye-Fei Yuan J. Anton Zensus Shuo Zhang Guang-Yao Zhao Shan-Shan Zhao
This is my paper · ORCID
classification astro-ph.HEastro-ph.GAastro-ph.IM
keywords activegalacticnucleirelativisticjetssub-parsecVLBIcoresbrightnesstemperatureBlandford-Königlmodeljetaccelerationmagneticenergydissipation
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

Radio observations of active galactic nuclei show a bright "core" whose apparent position shifts toward the black hole as the observing frequency rises, so multi-frequency measurements effectively scan along the jet. Combining the first 230 GHz VLBI images of sixteen AGN with archival 2–86 GHz data, this paper extracts power-law scalings of core flux density, size, and brightness temperature: $S_\nu\propto\nu^{-0.43\pm0.13}$, $\theta\propto\nu^{-0.64\pm0.05}$, $T_\mathrm{b}\propto\nu^{-0.95\pm0.13}$. The standard conical-jet model predicts a flat brightness temperature and $\theta\propto\nu^{-1}$, so the measured $\nu^{-1}$ decline in $T_\mathrm{b}$ indicates that conditions inside the jet change with distance from the black hole. The authors conclude that the jet material must either accelerate in bulk (Doppler factor growing as $\delta\propto r^{\le0.5}$) or convert magnetic energy into particle energy, or both, with magnetic field strength falling steeply as $B\propto r^{-2.9}$. If correct, this locates the main jet acceleration and energy conversion within the innermost parsec, roughly $10^5$ gravitational radii of the black hole.

What carries the argument

The load-bearing identity is the multi-frequency core-brightness relation. At each frequency $\nu$ the VLBI core is the $\tau=1$ synchrotron photosphere at distance $r=A\,\nu^{-1/k_r}$ (with $k_r=1$ in the canonical equipartition BK model), and $T_\mathrm{b}=1.22\times10^9\,S_\nu\,\nu^{-2}\,\theta^{-2}(1+z)$ converts measured flux density and angular size into brightness temperature. The BK model's flat-$T_\mathrm{b}$ prediction follows from $S_\nu\approx$ const and $\theta\propto\nu^{-1}$; the measured shallow $\theta\propto\nu^{-0.64}$ slope and slightly falling $S_\nu\propto\nu^{-0.43}$ compound into $T_\mathrm{b}\propto\nu^{-1.0}$, and hence into $T_\mathrm{b}\propto r$. The second relation is $B\approx1.4\times10^{21}\,\nu\,T_\mathrm{b}^{-2}$ G, which turns the measured $T_\mathrm{b}(\nu)$ into $B(\nu)$ and then $B(r)$. These two identities carry the entire argument; the parameter choices (equipartition, $\gamma_j=10$, $\phi=0.01$ rad) enter only through the constant converting $\nu$ to $r$, not through the slopes.

What would settle it

Measure core flux, size, and spectral index simultaneously at 86, 230, and 345 GHz for several of these sources in a single epoch; if the synchrotron turnover frequency lies below 230 GHz, the $T_\mathrm{b}\propto\nu^{-1}$ decline is an opacity effect rather than evidence for acceleration, whereas a flat or inverted 345 GHz spectrum with $\theta$ continuing to shrink as $\sim\nu^{-0.6}$ would confirm the acceleration and energy-conversion reading.

Watch

Extended reading notes

Core claim

On the paper's own terms, the discovery is that the canonical BK model fails when pushed to 230 GHz. For the EHT+ sample of sixteen AGN, per-source power-law fits aggregated over the sample give $T_\mathrm{b}\propto\nu^{-0.95\pm0.13}$ across 15–230 GHz in the host frame, which, through the core-shift relation $r\propto\nu^{-1/k_r}$ with $k_r\simeq1$, becomes $T_\mathrm{b}\propto r^{0.95\pm0.13}$: the core plasma is systematically brighter and hotter farther from the black hole. Because $T_\mathrm{b}\propto\delta\,\eta^{2/17}$ for self-absorbed synchrotron emission, this radial growth requires the Doppler factor $\delta$ or the particle-to-magnetic energy ratio $\eta$ to grow with radius; the authors cast both as a magnetically accelerated, magnetically dominated inner jet. The same data yield $B\propto r^{-2.89\pm0.26}$, steeper than the BK model's $r^{-1}$ perpendicular-field scaling, which they interpret as evidence for poloidal field dominance and efficient magnetic energy dissipation in the sub-parsec jet.

Load-bearing premise

The key assumption is that every VLBI core stays optically thick and self-absorbed up to 230 GHz; if a core becomes optically thin at high frequency, the observed drop in brightness temperature is just the expected spectral turnover and carries no acceleration signal.

Editorial extensions

If this is right

  • If the optically thick cores are confirmed, the canonical conical-jet model with constant Lorentz factor and constant energy partition is excluded across 15–230 GHz, so jet acceleration must begin well inside 1 pc.
  • The inferred Doppler-factor growth $\delta\propto r^{\le0.5}$ means much of the bulk acceleration happens within about $10^5$ gravitational radii, consistent with magnetic (Poynting-flux dominated) launching.
  • The steep magnetic-field slope $B\propto r^{-2.9}$ implies that field strength falls faster than the $r^{-1}$ expected for a toroidal component, favoring poloidal fields and magnetic dissipation or reconnection in the inner jet.
  • At lower frequencies (2–5 GHz) the data flatten toward the BK expectations, so the standard model remains viable on parsec and larger scales even while it fails on sub-parsec scales.
  • Breaking the degeneracy between acceleration and energy conversion will require per-source, frequency-dependent Doppler corrections from jet kinematics or variability.

Reading between the lines

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

  • A direct test the paper does not perform: simultaneous multi-frequency core-shift measurements between 86, 230, and 345 GHz would measure $r(\nu)$ empirically rather than assume it, and would distinguish geometric (parabolic) effects from genuine acceleration.
  • The EHT+ sample mixes flaring quasars, BL Lacs, and radio galaxies; if snapshot 230 GHz observations preferentially catch high states, the population-level $T_\mathrm{b}\propto\nu^{-0.95}$ could be partly a variability-selection artifact, and repeated 230 GHz epochs for the same sources would test whether the slope is stable.
  • If the optically-thick assumption fails first, the steep $B\propto r^{-3}$ slope would vanish as well, because the magnetic-field estimate is built on the same $T_\mathrm{b}(\nu)$; the two conclusions stand or fall together.
  • The RadioAstron measurements reaching $10^{14}$ K already strain the incoherent-synchrotron interpretation, and the same physics—scattering substructure or non-equipartition cores—could also affect the 230 GHz cores, so independent estimates of optical depth are the cleanest way to confirm the paper's story.
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Editorial analysis

A structured set of objections, weighed in public.

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

Referee Report

4 major / 5 minor

Summary. The paper compiles the 2017 EHT 230 GHz VLBI core measurements for 16 AGN, adds lower-frequency (2–86 GHz) data from surveys, models seven previously unpublished sources with circular Gaussians, and fits power laws to core flux density, size, and brightness temperature versus host-frame frequency over 15–230 GHz. It finds Sν ∝ ν^-0.43, θ ∝ ν^-0.64, and Tb ∝ ν^-0.95, interprets the Tb decline as a deviation from the Blandford–Königl jet model, and derives a magnetic-field radial slope B ∝ r^-2.9 and a Doppler-factor evolution δ ∝ r^≤0.5. The conclusion is that bulk acceleration and/or magnetic-to-particle energy transfer are required.

Significance. If the optically-thick core assumption holds at 230 GHz, this paper provides the first 230 GHz statistical view of sub-parsec jets and a strong constraint on jet acceleration models, built on a unique multi-frequency data set. The new 230 GHz core properties for seven AGN and the identification of a possible flux-density bias between EHT intra-site baselines and ALMA are useful contributions. The paper is explicit about its key assumptions and limitations, including the factor-of-two size uncertainties and the model-dependent character of the B(r) inference. However, the central physical conclusion is conditional on an assumption that the paper's own polarization data may violate, and several derived quantities are not independent of the measured Tb(ν) slope.

major comments (4)
  1. [§5 (crucial assumption), Appendix A] The central claim that Tb ∝ ν^-0.95 implies bulk acceleration or energy transfer rests on the assumption stated in Section 5: "we additionally make the crucial assumption that we observe self-absorbed, optically thick cores, and that they do not become fully optically thin at high observing frequencies." The paper's own data challenge this assumption: Appendix A reports core fractional polarizations of 65% for 1749+096 and 61% for 1055+018, values far above the ~10–20% expected for optically thick synchrotron cores, and explicitly notes this "may indicate ... a reduction of the optical depth at 230 GHz." If the cores are partially optically thin, the observed Tb decrease is a spectral turnover effect rather than a deviation from the BK model. The authors should provide a quantitative test of the optically thick assumption—for example, fitting a synchrotron self-absorption turnover to the core spectra, or comparing 86-to-230 GHz spectral indices with the predicted flat spectrum—or, failing that, present the acceleration/energy-transfer conclusion as explicitly conditional on τ(230 GHz) ≥ 1.
  2. [§5.3, Eq. (11)] The magnetic-field radial slope B ∝ r^-2.89 shown in the bottom panel of Fig. 5 is not an independent measurement. Equation (11) gives B ∝ ν Tb^-2; combined with the measured Tb ∝ ν^-0.95 and the BK mapping r ∝ ν^-1/kr (Eq. 10), this yields B ∝ ν^2.9 ∝ r^-2.9 for kr = 1, exactly as the paper notes in Section 5.3. The B(r) panel therefore restates the brightness-temperature slope under the assumed r(ν) mapping and cannot be cited as independent support for magnetic dissipation or a steep field profile. The authors should either derive B(r) from a separate estimator (e.g., core-shift measurements) or clearly label this panel as a model-dependent transformation of the Tb(ν) fit. They should also state the factor-of-25 upward bias of Eq. (11) relative to the Marscher (1983) estimator in the main text, not only in Section 4.2.
  3. [§3.1, Fig. 4] The quoted power-law slopes are estimated exclusively from the 15–230 GHz ground-based data, with the 2–8 GHz and RadioAstron points excluded post-hoc. While the resolution-bias argument is reasonable, the paper does not test the sensitivity of the central slopes to the chosen frequency window. The key result Tb ∝ ν^-0.95±0.13 could depend on the inclusion or exclusion of the 15 GHz (or 86 GHz) points. I request a robustness analysis: re-fit the slopes including 8 GHz data, excluding 15 GHz data, or restricting to sources with measurements at both 86 and 230 GHz. Without such a test, it is unclear whether the deviation from the BK flat-Tb prediction is a genuine population trend or a consequence of the selected frequency range.
  4. [§2.2, Table A.1, §3.1] The seven newly modeled sources have no reported formal uncertainties on their core size, flux density, or brightness temperature; Table A.1 states "we refrain from reporting untrustworthy uncertainties" and gives only a "conservative upper limit ... a factor of two difference." Since these seven sources make up nearly half of the 230 GHz sample, the unweighted aggregation of individual slopes in Section 3.1 is likely to underestimate the error on the population slope. The authors should propagate a factor-of-two systematic uncertainty into the per-source Tb values and recompute the population mean and standard error, or at least demonstrate that the fitted slopes are unchanged within the quoted uncertainties.
minor comments (5)
  1. [§3.1, Table B.1] The text defines the population slope as the mean of individual slopes m±σ/√N, but Table B.1 shows that the "cosmology only" fit to the combined cloud gives a significantly steeper size slope (−0.80±0.07) than the default individual-sources value (−0.64±0.05); please clarify which quantity is used in Fig. 4 and discuss the discrepancy.
  2. [Appendix A, §3.3] The statement "we refrain from reporting untrustworthy uncertainties" is understandable, but the factor-of-two upper limit on core brightness temperature should be mentioned in Section 3.3 alongside Eq. (2), since the reader may not consult the appendix.
  3. [Throughout] There are typographical artifacts such as "di fferent", "di fficult", and "V olume" in the text and Table 1; these should be corrected before publication.
  4. [§4.1, Eq. (10)] The constant K in Eq. (10) is defined only by the preceding sentence; please give its value or an explicit expression in terms of the assumed model parameters (B1, N1, ϕ, δ, etc.).
  5. [§5.2] The sentence "we find a constant intrinsic brightness temperature for a physically reasonable δ∝ν^-0.5_int" is hard to follow; the logic would be clearer if the assumption Tb,eq = const was stated before Eq. (12).

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the paper's B(r) and δ(r) profiles are explicit algebraic consequences of the measured Tb(ν) slope, and the optically-thick assumption is a flagged external caveat, not a circular input.

full rationale

The load-bearing chain in this paper is: (i) direct VLBI observables Sν, θ, and Tb are measured from Gaussian fits and literature; (ii) power-law slopes are fit to these observables versus frequency; (iii) the BK model is used to map frequency to radius and to predict flat Tb; (iv) the observed Tb∝ν^-0.95 is compared with the BK expectation. Steps (iii)–(iv) are a model comparison, not a circular reduction. The B(r) profile in Fig. 5 is an explicit algebraic transformation of the same observables: Eq. 11 gives B∝νTb^-2, and with r∝ν^-1 the fitted slope is B∝r^-2.89. The paper states this directly ('since we measure Tb∝ν^-1, Eq. 11 gives B∝ν^3∝r^{-3kr}'), so it does not disguise the derived nature of B(r) as an independent prediction. Similarly, δ∝r^0.5 is derived by requiring constant intrinsic brightness temperature under η=const.; this is an interpretive consistency argument, not a fitted quantity renamed as a prediction. The 'crucial assumption' of optically thick cores at 230 GHz is an external physical assumption, and the paper itself flags the optical-depth alternative in Appendix A; this is a correctness caveat, not circularity. Self-citations (Lee et al. 2016a; Nair et al. 2019) supply standard BK parameter choices and previous trend indications, but the central deviation claim rests on the measured Tb slope and is not reduced to those citations. Hence no circular step was found.

Assumptions & free parameters 5 free parameters · 5 assumptions · 0 invented entities

The central observational claim (Tb declines with frequency) does not depend on free parameters, but the radial interpretation (δ(r), B(r)) relies on assumed BK model parameters (kr, γ, N1, φ, ι) and the optically-thick core assumption. The B(r) slope is a restatement of the Tb(ν) fit under the assumed r(ν) mapping.

free parameters (5)
  • kr (BK equipartition radial index) = 1 (assumed)
    Sets the mapping r ∝ ν^{-1/kr} in Eq. 10. All radial slopes (θ(r), Tb(r), B(r)) and the inferred δ(r) depend on this assumed value.
  • Bulk Lorentz factor γ_j = 10 (assumed)
    Used in the BK model distance scale K in Eq. 10 and Doppler factor normalization. Affects absolute distances and magnetic field strengths, not the power-law indices.
  • Electron density N1 at 1 pc = 5×10^3 cm^-3 (assumed)
    Used in the distance and magnetic field normalization, following Lee et al. (2016a).
  • Jet opening angle φ and viewing angle ι = φ=0.01 rad, ι=0.1 rad
    Used to set Doppler factor δ≈10 and the intrinsic opening angle; affects normalization.
  • Spectral index α = -0.5 (assumed)
    Adopted in the BK model definitions of kr, kb, and ε.
assumptions (5)
  • domain assumption Blandford-Königl jet model assumptions: conical jet, constant Lorentz factor, equipartition, B ∝ r^{-1}, N ∝ r^{-2}, kr=1
    Adopted in Section 4.1 to convert frequency to distance and interpret the data.
  • domain assumption VLBI core is the τ=1 synchrotron photosphere and remains optically thick up to 230 GHz
    Stated in Section 5 as a crucial assumption for interpreting Tb as an intrinsic property. If false, the Tb(ν) decline could be a spectral turnover effect.
  • domain assumption The brightest Gaussian component is the VLBI core
    Used in Section 3.2 to identify the core among multiple fitted components.
  • domain assumption Source variability and single-epoch 230 GHz measurements are representative
    Single-epoch 230 GHz snapshots are compared with multi-epoch lower-frequency surveys; variability can bias slopes, as discussed in Section 3.2.
  • domain assumption The sample of 16 AGN is representative enough for statistical averaging
    The EHT 2017 sample is a mix of science targets and calibrators, not a complete sample; selection effects are mentioned but not quantified.

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Cite this review

Pith. "Pith review of A multi-frequency study of sub-parsec jets with the Event Horizon Telescope." pith.science (2026). https://pith.science/paper/GII5OEPA

@misc{pith2026250105518,
  author       = {Pith},
  title        = {Pith review of: A multi-frequency study of sub-parsec jets with the Event Horizon Telescope},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/GII5OEPA}},
  note         = {Machine review of arXiv:2501.05518}
}
read the original abstract

The 2017 observing campaign of the Event Horizon Telescope (EHT) delivered the first very long baseline interferometry (VLBI) images at the observing frequency of 230 GHz, leading to a number of unique studies on black holes and relativistic jets from active galactic nuclei (AGN). In total, eighteen sources were observed: the main science targets, Sgr A* and M87 along with various calibrators. We investigated the morphology of the sixteen AGN in the EHT 2017 data set, focusing on the properties of the VLBI cores: size, flux density, and brightness temperature. We studied their dependence on the observing frequency in order to compare it with the Blandford-K\"onigl (BK) jet model. We modeled the source structure of seven AGN in the EHT 2017 data set using linearly polarized circular Gaussian components and collected results for the other nine AGN from dedicated EHT publications, complemented by lower frequency data in the 2-86 GHz range. Then, we studied the dependences of the VLBI core flux density, size, and brightness temperature on the frequency measured in the AGN host frame. We compared the observations with the BK jet model and estimated the magnetic field strength dependence on the distance from the central black hole. Our results indicate a deviation from the standard BK model, particularly in the decrease of the brightness temperature with the observing frequency. Either bulk acceleration of the jet material, energy transfer from the magnetic field to the particles, or both are required to explain the observations.

Figures

Figures reproduced from arXiv: 2501.05518 by the authors.

Figure 1
Figure 1. (u, v)-coverage for all sources observed during the EHT 2017 campaign, as summarized in [PITH_FULL_IMAGE:figures/full_fig_p004_1.png] view at source ↗
Figure 2
Figure 2. Models of the EHT sources obtained through (polarized) circular Gaussian model fitting with at least two components. Blue [PITH_FULL_IMAGE:figures/full_fig_p005_2.png] view at source ↗
Figure 3
Figure 3. Core brightness temperature against core synchrotron [PITH_FULL_IMAGE:figures/full_fig_p007_3.png] view at source ↗
Figures from the paper (2 more)
Figure 4
Figure 4. Figure 4: Measurements of the core flux density (top), size (mid [PITH_FULL_IMAGE:figures/full_fig_p007_4.png]
Figure 5
Figure 5. Figure 5: Core size (top), brightness temperature (middle) and mag [PITH_FULL_IMAGE:figures/full_fig_p009_5.png]

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