分类： 天文学 >> 天文学 提交时间： 2023-02-19
Hiroki Okino
Kazunori Akiyama
Keiichi Asada
José L. Gómez
Kazuhiro Hada
Mareki Honma
Thomas P. Krichbaum
Motoki Kino
Hiroshi Nagai
Uwe Bach
Lindy Blackburn
Katherine L. Bouman
Andrew Chael
Geoffrey B. Crew
Sheperd S. Doeleman
Vincent L. Fish
Ciriaco Goddi
Sara Issaoun
Michael D. Johnson
Svetlana Jorstad
摘要： The collimation of relativistic jets launched from the vicinity of supermassive black holes (SMBHs) at the centers of active galactic nuclei (AGN) is one of the key questions to understand the nature of AGN jets. However, little is known about the detailed jet structure for AGN like quasars since very high angular resolutions are required to resolve these objects. We present very long baseline interferometry (VLBI) observations of the archetypical quasar 3C 273 at 86 GHz, performed with the Global Millimeter VLBI Array, for the first time including the Atacama Large Millimeter/submillimeter Array. Our observations achieve a high angular resolution down to $\sim$60 ${\rm \mu}$as, resolving the innermost part of the jet ever on scales of $\sim 10^5$ Schwarzschild radii. Our observations, including close-in-time High Sensitivity Array observations of 3C 273 at 15, 22, and 43 GHz, suggest that the inner jet collimates parabolically, while the outer jet expands conically, similar to jets from other nearby low luminosity AGN. We discovered the jet collimation break around $10^{7}$ Schwarzschild radii, providing the first compelling evidence for structural transition in a quasar jet. The location of the collimation break for 3C 273 is farther downstream the sphere of gravitational influence (SGI) from the central SMBH. With the results for other AGN jets, our results show that the end of the collimation zone in AGN jets is governed not only by the SGI of the SMBH but also by the more diverse properties of the central nuclei.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Svetlana Jorstad
Maciek Wielgus
Rocco Lico
Sara Issaoun
Avery E. Broderick
Dominic W. Pesce
Jun Liu
Guang-Yao Zhao
Thomas P. Krichbaum
Lindy Blackburn
Chi-Kwan Chan
Michael Janssen
Venkatessh Ramakrishnan
Kazunori Akiyama
Antxon Alberdi
Juan Carlos Algaba
Katherine L. Bouman
Ilje Cho
Antonio Fuentes
Jose L. Gomez
摘要： We report on the observations of the quasar NRAO 530 with the Event Horizon Telescope (EHT) on 2017 April 5-7, when NRAO 530 was used as a calibrator for the EHT observations of Sagittarius A*. At z=0.902 this is the most distant object imaged by the EHT so far. We reconstruct the first images of the source at 230 GHz, at an unprecedented angular resolution of $\sim$ 20 $\mu$as, both in total intensity and in linear polarization. We do not detect source variability, allowing us to represent the whole data set with static images. The images reveal a bright feature located on the southern end of the jet, which we associate with the core. The feature is linearly polarized, with a fractional polarization of $\sim$5-8% and has a sub-structure consisting of two components. Their observed brightness temperature suggests that the energy density of the jet is dominated by the magnetic field. The jet extends over 60 $\mu$as along a position angle PA$\sim -$28$^\circ$. It includes two features with orthogonal directions of polarization (electric vector position angle, EVPA), parallel and perpendicular to the jet axis, consistent with a helical structure of the magnetic field in the jet. The outermost feature has a particularly high degree of linear polarization, suggestive of a nearly uniform magnetic field. Future EHT observations will probe the variability of the jet structure on ${\mu}$as scales, while simultaneous multi-wavelength monitoring will provide insight into the high energy emission origin.
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