A multifrequency study of sub-parsec jets with the Event Horizon Telescope
Authors: Röder Jan , Wielgus Maciek , Lobanov Andrei P. , Krichbaum Thomas P. , Nair Dhanya G. , Lee Sang-Sung , Ros Eduardo , Fish Vincent L. , Blackburn Lindy , Chan Chi-kwan , Issaoun Sara , Janssen Michael , Johnson Michael D. , Doeleman Sheperd S. , Bower Geoffrey C. , Crew Geoffrey B. , Tilanus Remo P. J. , Savolainen Tuomas , Violette Impellizzeri C. M. , Alberdi Antxon , Baczko Anne-Kathrin , Gómez José L. , Lu Ru-Sen , Paraschos Georgios F. , Traianou Efthalia , Goddi Ciriaco , Kim Daewon , Lisakov Mikhail , Kovalev Yuri Y. , Voitsik Petr A. , Sokolovsky Kirill V. , Akiyama Kazunori , Albentosa-Ruíz Ezequiel , Alef Walter , Carlos Algaba Juan , Anantua Richard , Asada Keiichi , Azulay Rebecca , Bach Uwe , Ball David , Baloković Mislav , Bandyopadhyay Bidisha , Barrett John , Bauböck Michi , Benson Bradford A. , Bintley Dan , Blundell Raymond , Bouman Katherine L. , Bremer Michael , Brinkerink Christiaan D. , Brissenden Roger , Britzen Silke , Broderick Avery E. , Broguiere Dominique , Bronzwaer Thomas , Bustamante Sandra , Byun Do-Young , Carlstrom John E. , Ceccobello Chiara , Chael Andrew , Chang Dominic O. , Chatterjee Koushik , Chatterjee Shami , Chen Ming-Tang , Chen Yongjun , Cheng Xiaopeng , Cho Ilje , Christian Pierre , Conroy Nicholas S. , Conway John E. , Cordes James M. , Crawford Thomas M. , Cruz-Osorio Alejandro , Cui Yuzhu , Curd Brandon , Dahale Rohan , Davelaar Jordy , De Laurentis Mariafelicia , Deane Roger , Dempsey Jessica , Desvignes Gregory , Dexter Jason , Dhruv Vedant , Dihingia Indu K. , Taylor Dougall Sean , Dzib Sergio A. , Eatough Ralph P. , Emami Razieh , Falcke Heino , Farah Joseph , Fomalont Edward , Alyson Ford H. , Foschi Marianna , Fraga-Encinas Raquel , Freeman William T. , Friberg Per , Fromm Christian M. , Fuentes Antonio , Galison Peter , Gammie Charles F. , García Roberto , Gentaz Olivier , Georgiev Boris , Gold Roman , Gómez-Ruiz Arturo I. , Gu Minfeng , Gurwell Mark , Hada Kazuhiro , Haggard Daryl , Haworth Kari , Hecht Michael H. , Hesper Ronald , Heumann Dirk , Ho Luis C. , Ho Paul , Honma Mareki , Huang Chih-Wei L. , Huang Lei , Hughes David H. , Ikeda Shiro , Inoue Makoto , James David J. , Jannuzi Buell T. , Jeter Britton , Jiang Wu , Jiménez-Rosales Alejandra , Jorstad Svetlana , Joshi Abhishek V. , Jung Taehyun , Karami Mansour , Karuppusamy Ramesh , Kawashima Tomohisa , Keating Garrett K. , Kettenis Mark , Kim Dong-Jin , Kim Jae-Young , Kim Jongsoo , Kim Junhan , Kino Motoki , Yi Koay Jun , Kocherlakota Prashant , Kofuji Yutaro , Koyama Shoko , Kramer Carsten , Kramer Joana A. , Kramer Michael , Kuo Cheng-Yu , La Bella Noemi , Lauer Tod R. , Lee Daeyoung , Kin Leung Po , Levis Aviad , Li Zhiyuan , Lico Rocco , Lindahl Greg , Lindqvist Michael , Liu Jun , Liu Kuo , Liuzzo Elisabetta , Lo Wen-Ping , Loinard Laurent , Lonsdale Colin J. , Lowitz Amy E. , MacDonald Nicholas R. , Mao Jirong , Marchili Nicola , Markoff Sera , Marrone Daniel P. , Marscher Alan P. , Martí-Vidal Iván , Matsushita Satoki , Matthews Lynn D. , Medeiros Lia , Menten Karl M. , Michalik Daniel , Mizuno Izumi , Mizuno Yosuke , Moran James M. , Moriyama Kotaro , Moscibrodzka Monika , Mulaudzi Wanga , Müller Cornelia , Müller Hendrik , Mus Alejandro , Musoke Gibwa , Myserlis Ioannis , Nadolski Andrew , Nagai Hiroshi , Nagar Neil M. , Nakamura Masanori , Narayanan Gopal , Natarajan Iniyan , Nathanail Antonios , Navarro Fuentes Santiago , Neilsen Joey , Neri Roberto , Ni Chunchong , Noutsos Aristeidis , Nowak Michael A. , Oh Junghwan , Okino Hiroki , Olivares Sánchez Héctor R. , Ortiz-León Gisela N. , Oyama Tomoaki , Özel Feryal , Palumbo Daniel C. M. , Park Jongho , Parsons Harriet , Patel Nimesh , Pen Ue-Li , Pesce Dominic W. , Piétu Vincent , Plambeck Richard , PopStefanija Aleksandar , Porth Oliver , Pötzl Felix M. , Prather Ben , Preciado-López Jorge A. , Principe Giacomo , Psaltis Dimitrios , Pu Hung-Yi , Ramakrishnan Venkatessh , Rao Ramprasad , Rawlings Mark G. , Ricarte Angelo , Ripperda Bart , Roelofs Freek , Rogers Alan , Romero-Cañizales Cristina , Roshanineshat Arash , Rottmann Helge , Roy Alan L. , Ruiz Ignacio , Ruszczyk Chet , Rygl Kazi L. J. , Sánchez Salvador , Sánchez-Argüelles David , Sánchez-Portal Miguel , Sasada Mahito , Satapathy Kaushik , Peter Schloerb F. , Schonfeld Jonathan , Schuster Karl-Friedrich , Shao Lijing , Shen Zhiqiang , Small Des , Won Sohn Bong , SooHoo Jason , David Sosapanta Salas León , Souccar Kamal , Stanway Joshua S. , Sun He , Tazaki Fumie , Tetarenko Alexandra J. , Tiede Paul , Titus Michael , Torne Pablo , Toscano Teresa , Trent Tyler , Trippe Sascha , Turk Matthew , van Bemmel Ilse , van Langevelde Huib J. , van Rossum Daniel R. , Vos Jesse , Wagner Jan , Ward-Thompson Derek , Wardle John , Washington Jasmin E. , Weintroub Jonathan , Wharton Robert , Wiik Kaj , Witzel Gunther , Wondrak Michael F. , Wong George N. , Wu Qingwen , Yadlapalli Nitika , Yamaguchi Paul , Yfantis Aristomenis , Yoon Doosoo , Young André , Young Ken , Younsi Ziri , Yu Wei , Yuan Feng , Yuan Ye-Fei , Anton Zensus J. , Zhang Shuo , Zhao Guang-Yao , Zhao Shan-Shan 
Published: January 2025

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. 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. In particular, we aimed to study the signatures of jet acceleration and magnetic energy conversion. 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. 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^ hinting at jet acceleration or efficient magnetic energy dissipation.