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
Kuo Liu
Gregory Desvignes
Ralph P. Eatough
Ramesh Karuppusamy
Michael Kramer
Pablo Torne
Robert Wharton
Shami Chatterjee
James M. Cordes
Geoffrey B. Crew
Ciriaco Goddi
Scott M. Ransom
Helge Rottmann
Federico Abbate
Geoffrey C. Bower
Christiaan D. Brinkerink
Heino Falcke
Aristeidis Noutsos
Antonio Hernandez-Gomez
Wu Jiang
摘要： We report on the first pulsar and transient survey of the Galactic Center (GC) with the Atacama Large Millimeter/submillimeter Array (ALMA). The observations were conducted during the Global Millimeter VLBI Array campaign in 2017 and 2018. We carry out searches using timeseries of both total intensity and other polarization components in the form of Stokes parameters. We incorporate acceleration and its derivative in the pulsar search, and also search in segments of the entire observation to compensate for potential orbital motion of the pulsar. While no new pulsar is found, our observations yield the polarization profile of the GC magnetar PSR J1745-2900 at mm-wavelength for the first time, which turns out to be nearly 100 % linearly polarized. Additionally, we estimate the survey sensitivity placed by both system and red noise, and evaluate its capability of finding pulsars in orbital motion with either Sgr A* or a binary companion. We show that the survey is sensitive to only the most luminous pulsars in the known population, and future observations with ALMA in Band-1 will deliver significantly deeper survey sensitivity on the GC pulsar population.
点击量
待评议
点击量
下载量
评论
