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Search: WFRF:(Han Kuo Chang)

  • Result 1-7 of 7
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2.
  • Akiyama, Kazunori, et al. (author)
  • The persistent shadow of the supermassive black hole of M 87: I. Observations, calibration, imaging, and analysis*
  • 2024
  • In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 681
  • Journal article (peer-reviewed)abstract
    • In April 2019, the Event Horizon Telescope (EHT) Collaboration reported the first-ever event-horizon-scale images of a black hole, resolving the central compact radio source in the giant elliptical galaxy M 87. These images reveal a ring with a southerly brightness distribution and a diameter of ∼42 μas, consistent with the predicted size and shape of a shadow produced by the gravitationally lensed emission around a supermassive black hole. These results were obtained as part of the April 2017 EHT observation campaign, using a global very long baseline interferometric radio array operating at a wavelength of 1.3 mm. Here, we present results based on the second EHT observing campaign, taking place in April 2018 with an improved array, wider frequency coverage, and increased bandwidth. In particular, the additional baselines provided by the Greenland telescope improved the coverage of the array. Multiyear EHT observations provide independent snapshots of the horizon-scale emission, allowing us to confirm the persistence, size, and shape of the black hole shadow, and constrain the intrinsic structural variability of the accretion flow. We have confirmed the presence of an asymmetric ring structure, brighter in the southwest, with a median diameter of 43.3-3.1+1.5 μas. The diameter of the 2018 ring is remarkably consistent with the diameter obtained from the previous 2017 observations. On the other hand, the position angle of the brightness asymmetry in 2018 is shifted by about 30 relative to 2017. The perennial persistence of the ring and its diameter robustly support the interpretation that the ring is formed by lensed emission surrounding a Kerr black hole with a mass ∼6.5× 109M. The significant change in the ring brightness asymmetry implies a spin axis that is more consistent with the position angle of the large-scale jet.
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3.
  • Kim, Jae-Young, et al. (author)
  • Event Horizon Telescope imaging of the archetypal blazar 3C 279 at an extreme 20 microarcsecond resolution
  • 2020
  • In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 640
  • Journal article (peer-reviewed)abstract
    • 3C 279 is an archetypal blazar with a prominent radio jet that show broadband flux density variability across the entire electromagnetic spectrum. We use an ultra-high angular resolution technique - global Very Long Baseline Interferometry (VLBI) at 1.3mm (230 GHz) - to resolve the innermost jet of 3C 279 in order to study its fine-scale morphology close to the jet base where highly variable-ray emission is thought to originate, according to various models. The source was observed during four days in April 2017 with the Event Horizon Telescope at 230 GHz, including the phased Atacama Large Millimeter/submillimeter Array, at an angular resolution of ∼20 μas (at a redshift of z = 0:536 this corresponds to ∼0:13 pc ∼ 1700 Schwarzschild radii with a black hole mass MBH = 8 × 108 M⊙). Imaging and model-fitting techniques were applied to the data to parameterize the fine-scale source structure and its variation.We find a multicomponent inner jet morphology with the northernmost component elongated perpendicular to the direction of the jet, as imaged at longer wavelengths. The elongated nuclear structure is consistent on all four observing days and across diffierent imaging methods and model-fitting techniques, and therefore appears robust. Owing to its compactness and brightness, we associate the northern nuclear structure as the VLBI "core". This morphology can be interpreted as either a broad resolved jet base or a spatially bent jet.We also find significant day-to-day variations in the closure phases, which appear most pronounced on the triangles with the longest baselines. Our analysis shows that this variation is related to a systematic change of the source structure. Two inner jet components move non-radially at apparent speeds of ∼15 c and ∼20 c (∼1:3 and ∼1:7 μas day-1, respectively), which more strongly supports the scenario of traveling shocks or instabilities in a bent, possibly rotating jet. The observed apparent speeds are also coincident with the 3C 279 large-scale jet kinematics observed at longer (cm) wavelengths, suggesting no significant jet acceleration between the 1.3mm core and the outer jet. The intrinsic brightness temperature of the jet components are ≤1010 K, a magnitude or more lower than typical values seen at ≥7mm wavelengths. The low brightness temperature and morphological complexity suggest that the core region of 3C 279 becomes optically thin at short (mm) wavelengths.
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4.
  • Lu, R.S., et al. (author)
  • A ring-like accretion structure in M87 connecting its black hole and jet
  • 2023
  • In: Nature. - 0028-0836 .- 1476-4687. ; 616:7958, s. 686-690
  • Journal article (peer-reviewed)abstract
    • The nearby radio galaxy M87 is a prime target for studying black hole accretion and jet formation1,2. Event Horizon Telescope observations of M87 in 2017, at a wavelength of 1.3 mm, revealed a ring-like structure, which was interpreted as gravitationally lensed emission around a central black hole3. Here we report images of M87 obtained in 2018, at a wavelength of 3.5 mm, showing that the compact radio core is spatially resolved. High-resolution imaging shows a ring-like structure of [Formula: see text] Schwarzschild radii in diameter, approximately 50% larger than that seen at 1.3 mm. The outer edge at 3.5 mm is also larger than that at 1.3 mm. This larger and thicker ring indicates a substantial contribution from the accretion flow with absorption effects, in addition to the gravitationally lensed ring-like emission. The images show that the edge-brightened jet connects to the accretion flow of the black hole. Close to the black hole, the emission profile of the jet-launching region is wider than the expected profile of a black-hole-driven jet, suggesting the possible presence of a wind associated with the accretion flow.
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5.
  • Aad, G, et al. (author)
  • 2015
  • swepub:Mat__t
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  • Schuettpelz, Eric, et al. (author)
  • A community-derived classification for extant lycophytes and ferns
  • 2016
  • In: Journal of Systematics and Evolution. - : Wiley. - 1674-4918 .- 1759-6831. ; 54:6, s. 563-603
  • Journal article (peer-reviewed)abstract
    • Phylogeny has long informed pteridophyte classification. As our ability to infer evolutionary trees has improved, classifications aimed at recognizing natural groups have become increasingly predictive and stable. Here, we provide a modern, comprehensive classification for lycophytes and ferns, down to the genus level, utilizing a community-based approach. We use monophyly as the primary criterion for the recognition of taxa, but also aim to preserve existing taxa and circumscriptions that are both widely accepted and consistent with our understanding of pteridophyte phylogeny. In total, this classification treats an estimated 11 916 species in 337 genera, 51 families, 14 orders, and two classes. This classification is not intended as the final word on lycophyte and fern taxonomy, but rather a summary statement of current hypotheses, derived from the best available data and shaped by those most familiar with the plants in question. We hope that it will serve as a resource for those wanting references to the recent literature on pteridophyte phylogeny and classification, a framework for guiding future investigations, and a stimulus to further discourse.
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  • Result 1-7 of 7
Type of publication
journal article (6)
Type of content
peer-reviewed (6)
Author/Editor
Lu, R.S. (4)
Bach, U. (3)
Krichbaum, T. P. (3)
Savolainen, T. (3)
Roy, A. (3)
Marti-Vidal, Ivan, 1 ... (3)
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Hada, K. (3)
Crew, G. (3)
Kim, Jae-Young (3)
Akiyama, Kazunori (3)
Alef, Walter (3)
Bintley, Dan (3)
Britzen, Silke (3)
Broderick, Avery E. (3)
Byun, Do Young (3)
Chen, Ming Tang (3)
Conway, John, 1963 (3)
Huang, Chih Wei L. (3)
Inoue, Makoto (3)
Jung, Taehyun (3)
Kawashima, Tomohisa (3)
Koay, Jun Yi (3)
Koyama, Shoko (3)
Lindqvist, Michael, ... (3)
Lo, Wen-Ping (3)
Ros, Eduardo (3)
Tazaki, Fumie (3)
Nishioka, Hiroaki (3)
Algaba, Juan-Carlos (3)
Lobanov, A. P. (3)
Macdonald, N. R. (3)
Marscher, A. (3)
Park, Jongho (3)
Rottmann, H. (3)
Shen, Zhi Qiang (3)
Zensus, A.J. (3)
Han, Chih-Chiang (3)
Huang, Yau-De (3)
Jiang, Homin (3)
Kubo, Derek (3)
Liu, Ching-Tang (3)
Liu, Kuan-Yu (3)
Allardi, Alexander (3)
Chang, Shu-Hao (3)
Chang, Chih-Cheng (3)
Chang, Song-Chu (3)
Chen, Chung-Chen (3)
Chilson, R. (3)
Faber, Aaron (3)
Han, Kuo-Chang (3)
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University
Chalmers University of Technology (3)
Uppsala University (2)
Umeå University (1)
Stockholm University (1)
Linköping University (1)
Lund University (1)
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Karolinska Institutet (1)
Swedish University of Agricultural Sciences (1)
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Language
English (7)
Research subject (UKÄ/SCB)
Natural sciences (5)
Engineering and Technology (1)
Medical and Health Sciences (1)

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