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

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
² Instituto de Astrofísica de Andalucía-CSIC, Glorieta de la Astronomía s/n, E-18008 Granada, Spain
³ Astronomy Department, Universidad de Concepción, Casilla 160-C, Concepción, Chile
⁴ Korea Astronomy and Space Science Institute, Daedeok-daero 776, Yuseong-gu, Daejeon 34055, Republic of Korea
⁵ Massachusetts Institute of Technology Haystack Observatory, 99 Millstone Road, Westford, MA 01886, USA
⁶ Black Hole Initiative at Harvard University, 20 Garden Street, Cambridge, MA 02138, USA
⁷ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
⁸ Steward Observatory and Department of Astronomy, University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721, USA
⁹ Data Science Institute, University of Arizona, 1230 N. Cherry Ave., Tucson, AZ 85721, USA
¹⁰ Program in Applied Mathematics, University of Arizona, 617 N. Santa Rita, Tucson, AZ 85721, USA
¹¹ NASA Hubble Fellowship Program, Einstein Fellow, USA
¹² Department of Astrophysics, Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University, P.O. Box 9010 6500 GL Nijmegen, The Netherlands
¹³ Institute of Astronomy and Astrophysics, Academia Sinica, 645 N. A’ohoku Place, Hilo, HI 96720, USA
¹⁴ Department of Physics and Astronomy, University of Hawaii at Manoa, 2505 Correa Road, Honolulu, HI 96822, USA
¹⁵ Leiden Observatory, Leiden University, Postbus 2300, 9513 RA, Leiden, The Netherlands
¹⁶ Netherlands Organisation for Scientific Research (NWO), Postbus 93138, 2509 AC Den Haag, The Netherlands
¹⁷ Aalto University Department of Electronics and Nanoengineering, PL 15500, FI-00076 Aalto, Finland
¹⁸ Aalto University Metsähovi Radio Observatory, Metsähovintie 114, FI-02540 Kylmälä, Finland
¹⁹ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
²⁰ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, SE-43992 Onsala, Sweden
²¹ Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, People’s Republic of China
²² Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, R. do Matão, 1226, São Paulo, SP 05508-090, Brazil
²³ Dipartimento di Fisica, Universitá degli Studi di Cagliari, SP Monserrato-Sestu km 0.7, I-09042 Monserrato (CA), Italy
²⁴ INAF – Osservatorio Astronomico di Cagliari, via della Scienza 5, I-09047 Selargius (CA), Italy
²⁵ INFN, sezione di Cagliari, I-09042 Monserrato (CA), Italy
²⁶ Instituto de Física, Pontificia Universidad Católica de Valparaíso, Casilla 4059, Valparaíso, Chile
²⁷ Independent researcher
²⁸ Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 West Green Street, Urbana, IL 61801, USA
²⁹ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka,Tokyo 181-8588, Japan
³⁰ Departament d’Astronomia i Astrofísica, Universitat de Valéncia, streetC. Dr. Moliner 50 E-46100 Burjassot, Valéncia, Spain
³¹ Department of Physics, Faculty of Science, Universiti Malaya, 50603 Kuala Lumpur, Malaysia
³² Department of Physics & Astronomy, The University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249, USA
³³ Institute of Astronomy and Astrophysics, Academia Sinica, 11F of Astronomy-Mathematics Building, AS/NTU No. 1, Sec. 4, Roosevelt Rd., Taipei 106216, Taiwan, R.O.C.
³⁴ Observatori Astronómic, Universitat de Valéncia, C. Catedrático José Beltrán 2, E-46980 Paterna, Valéncia, Spain
³⁵ Yale Center for Astronomy & Astrophysics, Yale University, 52 Hillhouse Avenue, New Haven, CT 06511, USA
³⁶ Department of Physics, University of Illinois, 1110 West Green Street, Urbana, IL 61801, USA
³⁷ Fermi National Accelerator Laboratory, MS209, P.O. Box 500 Batavia, IL 60510, USA
³⁸ Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA
³⁹ East Asian Observatory, 660 N. A’ohoku Place, Hilo, HI 96720, USA
⁴⁰ James Clerk Maxwell Telescope (JCMT), 660 N. A’ohoku Place, Hilo, HI 96720, USA
⁴¹ California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA
⁴² Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, F-38406 Saint Martin d’Hères, France
⁴³ Perimeter Institute for Theoretical Physics, 31 Caroline Street North, Waterloo ON N2L 2Y5, Canada
⁴⁴ Department of Physics and Astronomy, University of Waterloo, 200 University Avenue West, Waterloo ON N2L 3G1, Canada
⁴⁵ Waterloo Centre for Astrophysics, University of Waterloo, Waterloo ON N2L 3G1, Canada
⁴⁶ Department of Astronomy, University of Massachusetts, Amherst, MA 01003, USA
⁴⁷ University of Science and Technology, Gajeong-ro 217, Yuseong-gu, Daejeon 34113, Republic of Korea
⁴⁸ Kavli Institute for Cosmological Physics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA
⁴⁹ Department of Physics, University of Chicago, 5720 South Ellis Avenue, Chicago, IL 60637, USA
⁵⁰ Enrico Fermi Institute, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA
⁵¹ Princeton Gravity Initiative, Jadwin Hall, Princeton University, Princeton, NJ 08544, USA
⁵² Cornell Center for Astrophysics and Planetary Science, Cornell University, Ithaca, NY 14853, USA
⁵³ Key Laboratory of Radio Astronomy and Technology, Chinese Academy of Sciences, A20 Datun Road, Chaoyang District Beijing 100101, People’s Republic of China
⁵⁴ Department of Astronomy, Yonsei University, Yonsei-ro 50, Seodaemun-gu, 03722 Seoul, Republic of Korea
⁵⁵ Physics Department, Fairfield University, 1073 North Benson Road, Fairfield, CT 06824, USA
⁵⁶ Instituto de Astronomía, Universidad Nacional Autónoma de México (UNAM), Apdo Postal 70-264, Ciudad de México, Mexico
⁵⁷ Institut für Theoretische Physik, Goethe-Universität Frankfurt, Max-von-Laue-Straße 1, D-60438 Frankfurt am Main, Germany
⁵⁸ Research Center for Astronomical Computing, Zhejiang Laboratory, Hangzhou 311100, People’s Republic of China
⁵⁹ Tsung-Dao Lee Institute, Shanghai Jiao Tong University, Shengrong Road 520, Shanghai 201210, People’s Republic of China
⁶⁰ Department of Astronomy and Columbia Astrophysics Laboratory, Columbia University, 500 W. 120th Street, New York, NY 10027, USA
⁶¹ Center for Computational Astrophysics, Flatiron Institute, 162 Fifth Avenue, New York, NY 10010, USA
⁶² Dipartimento di Fisica “E. Pancini”, Universitá di Napoli “Federico II”, Compl. Univ. di Monte S. Angelo, Edificio G, Via Cinthia, I-80126 Napoli, Italy
⁶³ INFN Sez. di Napoli, Compl. Univ. di Monte S. Angelo, Edificio G, Via Cinthia, I-80126 Napoli, Italy
⁶⁴ Wits Centre for Astrophysics, University of the Witwatersrand, 1 Jan Smuts Avenue, Braamfontein, Johannesburg 2050, South Africa
⁶⁵ Department of Physics, University of Pretoria, Hatfield, Pretoria 0028, South Africa
⁶⁶ Centre for Radio Astronomy Techniques and Technologies, Department of Physics and Electronics, Rhodes University, Makhanda 6140, South Africa
⁶⁷ ASTRON, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
⁶⁸ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen, F-92195 Meudon, France
⁶⁹ JILA and Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309, USA
⁷⁰ National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District Beijing 100101, PR China
⁷¹ Las Cumbres Observatory, 6740 Cortona Drive, Suite 102, Goleta, CA 93117-5575, USA
⁷² Department of Physics, University of California, Santa Barbara, CA 93106-9530, USA
⁷³ Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 32-D476, 77 Massachusetts Ave., Cambridge, MA 02142, USA
⁷⁴ Google Research, 355 Main St., Cambridge, MA 02142, USA
⁷⁵ Institut für Theoretische Physik und Astrophysik, Julius-Maximilian-Universität Würzburg, Emil-Fischer-Straße 31, 97074 Würzburg, Germany
⁷⁶ Department of History of Science, Harvard University, Cambridge, MA 02138, USA
⁷⁷ Department of Physics, Harvard University, Cambridge, MA 02138, USA
⁷⁸ NCSA, University of Illinois, 1205 W. Clark St., Urbana, IL 61801, USA
⁷⁹ Institute for Mathematics and Interdisciplinary Center for Scientific Computing, Heidelberg University, Im Neuenheimer Feld 205, Heidelberg 69120, Germany
⁸⁰ Institut für Theoretische Physik, Universität Heidelberg, Philosophenweg 16, 69120 Heidelberg, Germany
⁸¹ CP3-Origins, University of Southern Denmark, Campusvej 55, 5230 Odense, Denmark
⁸² Instituto Nacional de Astrofísica, Óptica y Electrónica. Apartado Postal 51 y 216, 72000 Puebla Pue., Mexico
⁸³ Consejo Nacional de Humanidades, Ciencia y Tecnología, Av. Insurgentes Sur 1582, 03940 Ciudad de México, Mexico
⁸⁴ Key Laboratory for Research in Galaxies and Cosmology, Chinese Academy of Sciences, Shanghai 200030, People’s Republic of China
⁸⁵ Mizusawa VLBI Observatory, National Astronomical Observatory of Japan, 2-12 Hoshigaoka, Mizusawa, Oshu, Iwate 023-0861, Japan
⁸⁶ Department of Astronomical Science, The Graduate University for Advanced Studies (SOKENDAI), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁸⁷ Department of Physics, McGill University, 3600 rue University, Montréal QC H3A 2T8, Canada
⁸⁸ Trottier Space Institute at McGill, 3550 rue University, Montréal QC H3A 2A7, Canada
⁸⁹ NOVA Sub-mm Instrumentation Group, Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 AD Groningen, The Netherlands
⁹⁰ Department of Astronomy, School of Physics, Peking University, Beijing 100871, People’s Republic of China
⁹¹ Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, People’s Republic of China
⁹² Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
⁹³ The Institute of Statistical Mathematics, 10-3 Midori-cho, Tachikawa, Tokyo 190-8562, Japan
⁹⁴ Department of Statistical Science, The Graduate University for Advanced Studies (SOKENDAI), 10-3 Midori-cho, Tachikawa, Tokyo 190-8562, Japan
⁹⁵ Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa 277-8583, Japan
⁹⁶ ASTRAVEO LLC, PO Box 1668 Gloucester MA 01931, USA
⁹⁷ Applied Materials Inc., 35 Dory Road, Gloucester MA 01930, USA
⁹⁸ Institute for Astrophysical Research, Boston University, 725 Commonwealth Ave., Boston, MA 02215, USA
⁹⁹ Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8582, Japan
¹⁰⁰ Joint Institute for VLBI ERIC (JIVE), Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
¹⁰¹ Department of Physics, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Eonyang-eup, Ulju-gun, Ulsan 44919, Republic of Korea
¹⁰² Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
¹⁰³ Kogakuin University of Technology & Engineering, Academic Support Center, 2665-1 Nakano, Hachioji, Tokyo 192-0015, Japan
¹⁰⁴ Graduate School of Science and Technology, Niigata University, 8050 Ikarashi 2-no-cho, Nishi-ku, Niigata 950-2181, Japan
¹⁰⁵ Physics Department, National Sun Yat-Sen University, No. 70, Lien-Hai Road, Kaosiung City 80424, Taiwan, R.O.C.
¹⁰⁶ National Optical Astronomy Observatory, 950 N. Cherry Ave., Tucson, AZ 85719, USA
¹⁰⁷ Department of Physics, The Chinese University of Hong Kong, Shatin, N. T., Hong Kong
¹⁰⁸ School of Astronomy and Space Science, Nanjing University, Nanjing 210023, People’s Republic of China
¹⁰⁹ Key Laboratory of Modern Astronomy and Astrophysics, Nanjing University, Nanjing 210023, People’s Republic of China
¹¹⁰ INAF-Istituto di Radioastronomia, Via P. Gobetti 101, I-40129 Bologna, Italy
¹¹¹ INAF-Istituto di Radioastronomia & Italian ALMA Regional Centre, Via P. Gobetti 101, I-40129 Bologna, Italy
¹¹² Department of Physics, National Taiwan University, No. 1, Sec. 4, Roosevelt Rd., Taipei 106216, Taiwan, R.O.C
¹¹³ Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Morelia 58089, Mexico
¹¹⁴ David Rockefeller Center for Latin American Studies, Harvard University, 1730 Cambridge Street, Cambridge, MA 02138, USA
¹¹⁵ Yunnan Observatories, Chinese Academy of Sciences, 650011 Kunming, Yunnan Province, People’s Republic of China
¹¹⁶ Center for Astronomical Mega-Science, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012, People’s Republic of China
¹¹⁷ Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, 650011 Kunming, People’s Republic of China
¹¹⁸ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
¹¹⁹ Gravitation and Astroparticle Physics Amsterdam (GRAPPA) Institute, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
¹²⁰ Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, NJ 08544, USA
¹²¹ Science Support Office, Directorate of Science, European Space Research and Technology Centre (ESA/ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
¹²² Department of Astronomy and Astrophysics, University of Chicago, Eckhardt, 5640 S Ellis Ave, Chicago, IL 60637, USA
¹²³ School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People’s Republic of China
¹²⁴ National Radio Astronomy Observatory, P.O. Box O Socorro, NM 87801, USA
¹²⁵ Institut de Radioastronomie Millimétrique (IRAM), Avenida Divina Pastora 7, Local 20, E-18012 Granada, Spain
¹²⁶ National Institute of Technology, Hachinohe College, 16-1 Uwanotai, Tamonoki, Hachinohe City, Aomori 039-1192, Japan
¹²⁷ Research Center for Astronomy, Academy of Athens, Soranou Efessiou 4, 115 27 Athens, Greece
¹²⁸ Department of Physics, Villanova University, 800 Lancaster Avenue, Villanova, PA 19085, USA
¹²⁹ Physics Department, Washington University, CB 1105, St. Louis, MO 63130, USA
¹³⁰ Departamento de Matemática da Universidade de Aveiro and Centre for Research and Development in Mathematics and Applications (CIDMA), Campus de Santiago, 3810-193, Aveiro, Portugal
¹³¹ School of Physics, Georgia Institute of Technology, 837 State St NW, Atlanta, GA 30332, USA
¹³² School of Space Research, Kyung Hee University, 1732, Deogyeong-daero, Giheung-gu, Yongin-si, Gyeonggi-do 17104, Republic of Korea
¹³³ Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto stateON M5S 3H8, Canada
¹³⁴ Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4, Canada
¹³⁵ Canadian Institute for Advanced Research, 180 Dundas St West, Toronto, ON M5G 1Z8, Canada
¹³⁶ Radio Astronomy Laboratory, University of California, Berkeley, CA 94720, USA
¹³⁷ Institute of Astrophysics, Foundation for Research and Technology – Hellas, Voutes, 7110 Heraklion, Greece
¹³⁸ Dipartimento di Fisica, Universitá di Trieste, I-34127 Trieste, Italy
¹³⁹ INFN Sez. di Trieste, I-34127 Trieste, Italy
¹⁴⁰ Department of Physics, National Taiwan Normal University, No. 88, Sec. 4, Tingzhou Rd., Taipei 116, Taiwan, R.O.C.
¹⁴¹ Center of Astronomy and Gravitation, National Taiwan Normal University, No. 88, Sec. 4, Tingzhou Road, Taipei 116, Taiwan, R.O.C.
¹⁴² Finnish Centre for Astronomy with ESO, FI-20014 University of Turku, Finland
¹⁴³ Gemini Observatory/NSF NOIRLab, 670 N. A’ohōkū Place, Hilo, HI 96720, USA
¹⁴⁴ Department of Physics, University of Toronto, 60 St. George Street, Toronto, ON M5S 1A7, Canada
¹⁴⁵ Department of Physics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan
¹⁴⁶ Hiroshima Astrophysical Science Center, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima Hiroshima 739-8526, Japan
¹⁴⁷ Institut de Radioastronomie de Millimétrique (IRAM), 300 Rue de la Piscine, 38400 Saint-Martin-d’Hères, France
¹⁴⁸ Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE, UK
¹⁴⁹ National Biomedical Imaging Center, Peking University, Beijing 100871, People’s Republic of China
¹⁵⁰ College of Future Technology, Peking University, Beijing 100871, People’s Republic of China
¹⁵¹ Department of Physics and Astronomy, University of Lethbridge, Lethbridge, Alberta T1K 3M4, Canada
¹⁵² Department of Physics and Astronomy, Seoul National University, Gwanak-gu, Seoul 08826, Republic of Korea
¹⁵³ University of New Mexico, Department of Physics and Astronomy, Albuquerque, NM 87131, USA
¹⁵⁴ Physics Department, Brandeis University, 415 South Street, Waltham, MA 02453, USA
¹⁵⁵ Tuorla Observatory, Department of Physics and Astronomy, FI-20014 University of Turku, Finland
¹⁵⁶ Radboud Excellence Fellow of Radboud University, Nijmegen, The Netherlands
¹⁵⁷ School of Natural Sciences, Institute for Advanced Study, 1 Einstein Drive, Princeton, NJ 08540, USA
¹⁵⁸ School of Physics, Huazhong University of Science and Technology, Wuhan, Hubei 430074, People’s Republic of China
¹⁵⁹ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
¹⁶⁰ Center for Astronomy and Astrophysics and Department of Physics, Fudan University, Shanghai 200438, People’s Republic of China
¹⁶¹ Astronomy Department, University of Science and Technology of China, Hefei 230026, People’s Republic of China
¹⁶² Department of Physics and Astronomy, Michigan State University, 567 Wilson Rd, East Lansing MI 48824, USA

^⋆ Corresponding author; jroeder.astro@gmail.com

Received: 14 October 2024
Accepted: 1 January 2025

Abstract

Context. 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, including the main science targets, Sgr A* and M 87, and various calibrators. Sixteen sources were AGN.

Aims. 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-Königl (BK) jet model. In particular, we aimed to study the signatures of jet acceleration and magnetic energy conversion.

Methods. We modeled the source structure of seven AGN in the EHT 2017 data set using linearly polarized circular Gaussian components (1749+096, 1055+018, BL Lac, J0132–1654, J0006–0623, CTA 102, and 3C 454.3) and collected results for the other nine AGN from dedicated EHT publications, complemented by lower frequency data in the 2–86 GHz range. Combining these data into a multifrequency EHT+ data set, we studied the dependences of the VLBI core component flux density, size, and brightness temperature on the frequency measured in the AGN host frame (and hence on the distance from the central black hole), characterizing them with power law fits. We compared the observations with the BK jet model and estimated the magnetic field strength dependence on the distance from the central black hole.

Results. Our observations spanning event horizon to parsec scales indicate a deviation from the standard BK model, particularly in the decrease of the brightness temperature with the observing frequency. Only some of the discrepancies may be alleviated by tweaking the model parameters or the jet collimation profile. Either bulk acceleration of the jet material, energy transfer from the magnetic field to the particles, or both are required to explain the observations. For our sample, we estimate a general radial dependence of the Doppler factor δ ∝ r^≤0.5. This interpretation is consistent with a magnetically accelerated sub-parsec jet. We also estimate a steep decrease of the magnetic field strength with radius B ∝ r⁻³, hinting at jet acceleration or efficient magnetic energy dissipation.