Browsing by Author "Nakamura, M."

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  • The complex variability of blazars: Time-scales and periodicity analysis in S4 0954+65
    (2021-07-01) Raiteri, C. M.; Villata, M.; Larionov, V. M.; Jorstad, S. G.; Marscher, A. P.; Weaver, Z. R.; Acosta-Pulido, J. A.; Agudo, I.; Andreeva, T.; Arkharov, A.; Bachev, R.; Benítez, E.; Berton, M.; Björklund, I.; Borman, G. A.; Bozhilov, V.; Carnerero, M. I.; Carosati, D.; Casadio, C.; Chen, W. P.; Damljanovic, G.; D'Ammando, F.; Escudero, J.; Fuentes, A.; Giroletti, M.; Grishina, T. S.; Gupta, A. C.; Hagen-Thorn, V. A.; Hart, M.; Hiriart, D.; Hou, W. J.; Ivanov, D.; Kim, J. Y.; Kimeridze, G. N.; Konstantopoulou, C.; Kopatskaya, E. N.; Kurtanidze, O. M.; Kurtanidze, S. O.; Lähteenmäki, A.; Larionova, E. G.; Larionova, L. V.; Marchili, N.; Markovic, G.; Minev, M.; Morozova, D. A.; Myserlis, I.; Nakamura, M.; Nikiforova, A. A.; Nikolashvili, M. G.; Otero-Santos, J.; Ovcharov, E.; Pursimo, T.; Rahimov, I.; Righini, S.; Sakamoto, T.; Savchenko, S. S.; Semkov, E. H.; Shakhovskoy, D.; Sigua, L. A.; Stojanovic, M.; Strigachev, A.; Thum, C.; Tornikoski, M.; Traianou, E.; Troitskaya, Y. V.; Troitskiy, I. S.; Tsai, A.; Valcheva, A.; Vasilyev, A. A.; Vince, O.; Zaharieva, E.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Among active galactic nuclei, blazars show extreme variability properties. We here investigate the case of the BL Lac object S4 0954+65 with data acquired in 2019-2020 by the Transiting Exoplanet Survey Satellite (TESS) and by the Whole Earth Blazar Telescope (WEBT) Collaboration. The 2-min cadence optical light curves provided by TESS during three observing sectors of nearly 1 month each allow us to study the fast variability in great detail. We identify several characteristic short-term time-scales, ranging from a few hours to a few days. However, these are not persistent, as they differ in the various TESS sectors. The long-term photometric and polarimetric optical and radio monitoring undertaken by the WEBT brings significant additional information, revealing that (i) in the optical, long-term flux changes are almost achromatic, while the short-term ones are strongly chromatic; (ii) the radio flux variations at 37 GHz follow those in the optical with a delay of about 3 weeks; (iii) the range of variation of the polarization degree and angle is much larger in the optical than in the radio band, but the mean polarization angles are similar; (iv) the optical long-term variability is characterized by a quasi-periodicity of about 1 month. We explain the source behaviour in terms of a rotating inhomogeneous helical jet, whose pitch angle can change in time.
  • Ordered magnetic fields around the 3C 84 central black hole
    (2024-02-01) Paraschos, G. F.; Kim, J. Y.; Wielgus, M.; Röder, J.; Krichbaum, T. P.; Ros, E.; Agudo, I.; Myserlis, I.; Moscibrodzka, M.; Traianou, E.; Zensus, J. A.; Blackburn, L.; Chan, C. K.; Issaoun, S.; Janssen, M.; Johnson, M. D.; Fish, V. L.; Akiyama, K.; Alberdi, A.; Alef, W.; Algaba, J. C.; Anantua, R.; Asada, K.; Azulay, R.; Bach, U.; Baczko, A. K.; Ball, D.; Baloković, M.; Barrett, J.; Bauböck, M.; Benson, B. A.; Bintley, D.; Blundell, R.; Bouman, K. L.; Bower, G. C.; Boyce, H.; Bremer, M.; Brinkerink, C. D.; Brissenden, R.; Britzen, S.; Broderick, A. E.; Broguiere, D.; Bronzwaer, T.; Bustamante, S.; Byun, D. Y.; Carlstrom, J. E.; Ceccobello, C.; Chael, A.; Chang, D. O.; Chatterjee, K.; Chatterjee, S.; Chen, M. T.; Chen, Y.; Cheng, X.; Cho, I.; Christian, P.; Conroy, N. S.; Conway, J. E.; Cordes, J. M.; Crawford, T. M.; Crew, G. B.; Cruz-Osorio, A.; Cui, Y.; Dahale, R.; Davelaar, J.; De Laurentis, M.; Deane, R.; Dempsey, J.; Desvignes, G.; Dexter, J.; Dhruv, V.; Doeleman, S. S.; Dougal, S.; Dzib, S. A.; Eatough, R. P.; Emami, R.; Falcke, H.; Farah, J.; Fomalont, E.; Ford, H. A.; Foschi, M.; Fraga-Encinas, R.; Freeman, W. T.; Friberg, P.; Fromm, C. M.; Fuentes, A.; Galison, P.; Gammie, C. F.; García, R.; Gentaz, O.; Georgiev, B.; Goddi, C.; Gold, R.; Gómez-Ruiz, A. I.; Gómez, J. L.; Gu, M.; Gurwell, M.; Hada, K.; Haggard, D.; Haworth, K.; Hecht, M. H.; Hesper, R.; Heumann, D.; Ho, L. C.; Ho, P.; Honma, M.; Huang, C. L.; Huang, L.; Hughes, D. H.; Ikeda, S.; Impellizzeri, C. M.V.; Inoue, M.; James, D. J.; Jannuzi, B. T.; Jeter, B.; Jaing, W.; Jiménez-Rosales, A.; Jorstad, S.; Joshi, A. V.; Jung, T.; Karami, M.; Karuppusamy, R.; Kawashima, T.; Keating, G. K.; Kettenis, M.; Kim, D. J.; Kim, J.; Kino, M.; Koay, J. Y.; Kocherlakota, P.; Kofuji, Y.; Koch, P. M.; Koyama, S.; Kramer, C.; Kramer, J. A.; Kramer, M.; Kuo, C. Y.; La Bella, N.; Lauer, T. R.; Lee, D.; Lee, S. S.; Leung, P. K.; Levis, A.; Li, Z.; Lico, R.; Lindahl, G.; Lindqvist, M.; Lisakov, M.; Liu, J.; Liu, K.; Liuzzo, E.; Lo, W. P.; Lobanov, A. P.; Loinard, L.; Lonsdale, C. J.; Lowitz, A. E.; Lu, R. S.; MacDonald, N. R.; Mao, J.; Marchili, N.; Markoff, S.; Marrone, D. P.; Marscher, A. P.; Martí-Vidal, I.; Matsushita, S.; Matthews, L. D.; Medeiros, L.; Menten, K. M.; Michalik, D.; Mizuno, I.; Mizuno, Y.; Moran, J. M.; Moriyama, K.; Mulaudzi, W.; Müller, C.; Müller, H.; Mus, A.; Musoke, G.; Nadolski, A.; Nagai, H.; Nagar, N. M.; Nakamura, M.; Narayanan, G.; Natarajan, I.; Nathanail, A.; Navarro Fuentes, S.; Neilsen, J.; Neri, R.; Ni, C.; Noutsos, A.; Nowak, M. A.; Oh, J.; Okino, H.; Olivares, H.; Ortiz-León, G. N.; Oyama, T.; ÖZel, F.; Palumbo, D. C.M.; Park, J.; Parsons, H.; Patel, N.; Pen, U. L.; Piétu, V.; Plambeck, R.; Popstefanija, A.; Porth, O.; Pötzl, F. M.; Prather, B.; Preciado-López, J. A.; Psaltis, D.; Pu, H. Y.; Ramakrishnan, V.; Rao, R.; Rawlings, M. G.; Raymond, A. W.; Rezzolla, L.; Ricarte, A.; Ripperda, B.; Roelofs, F.; Rogers, A.; Romero-Cañizales, C.; Roshanineshat, A.; Rottmann, H.; Roy, A. L.; Ruiz, I.; Ruszczyk, C.; Rygl, K. L.J.; Sánchez, S.; Sánchez-Argüelles, D.; Sánchez-Portal, M.; Sasada, M.; Satapathy, K.; Savolainen, T.; Schloerb, F. P.; Schonfeld, J.; Schuster, K.; Shao, L.; Shen, Z.; Small, D.; Sohn, B. W.; Soohoo, J.; Sosapanta Salas, L. D.; Souccar, K.; Sun, H.; Tazaki, F.; Tetarenko, A. J.; Tiede, P.; Tilanus, R. P.J.; Titus, M.; Torne, P.; Toscano, T.; Trent, T.; Trippe, S.; Turk, M.; Van Bemmel, I.; Van Langevelde, H. J.; Van Rossum, D. R.; Vos, J.; Wagner, J.; Ward-Thompson, D.; Wardle, J.; Washington, J. E.; Weintroub, J.; Wharton, R.; Wiik, K.; Witzel, G.; Wondrak, M. F.; Wong, G. N.; Wu, Q.; Yadlapalli, N.; Yamaguchi, P.; Yfantis, A.; Yoon, D.; Young, A.; Young, K.; Younsi, Z.; Yu, W.; Yuan, F.; Yuan, Y. F.; Zhang, S.; Zhao, G. Y.; Zhao, S. S.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Context. 3C 84 is a nearby radio source with a complex total intensity structure, showing linear polarisation and spectral patterns. A detailed investigation of the central engine region necessitates the use of very-long-baseline interferometry (VLBI) above the hitherto available maximum frequency of 86 GHz. Aims. Using ultrahigh resolution VLBI observations at the currently highest available frequency of 228 GHz, we aim to perform a direct detection of compact structures and understand the physical conditions in the compact region of 3C 84. Methods. We used Event Horizon Telescope (EHT) 228 GHz observations and, given the limited (u, v)-coverage, applied geometric model fitting to the data. Furthermore, we employed quasi-simultaneously observed, ancillary multi-frequency VLBI data for the source in order to carry out a comprehensive analysis of the core structure. Results. We report the detection of a highly ordered, strong magnetic field around the central, supermassive black hole of 3C 84. The brightness temperature analysis suggests that the system is in equipartition. We also determined a turnover frequency of νm = (113 ± 4) GHz, a corresponding synchrotron self-absorbed magnetic field of BSSA = (2.9 ± 1.6) G, and an equipartition magnetic field of Beq = (5.2 ± 0.6) G. Three components are resolved with the highest fractional polarisation detected for this object (mnet = (17.0 ± 3.9)%). The positions of the components are compatible with those seen in low-frequency VLBI observations since 2017-2018. We report a steeply negative slope of the spectrum at 228 GHz. We used these findings to test existing models of jet formation, propagation, and Faraday rotation in 3C 84. Conclusions. The findings of our investigation into different flow geometries and black hole spins support an advection-dominated accretion flow in a magnetically arrested state around a rapidly rotating supermassive black hole as a model of the jet-launching system in the core of 3C 84. However, systematic uncertainties due to the limited (u, v)-coverage, however, cannot be ignored. Our upcoming work using new EHT data, which offer full imaging capabilities, will shed more light on the compact region of 3C 84.
  • A wide and collimated radio jet in 3C84 on the scale of a few hundred gravitational radii
    (2018-06-01) Giovannini, G.; Savolainen, T.; Orienti, M.; Nakamura, M.; Nagai, H.; Kino, M.; Giroletti, M.; Hada, K.; Bruni, G.; Kovalev, Y. Y.; Anderson, J. M.; D'Ammando, F.; Hodgson, J.; Honma, M.; Krichbaum, T. P.; Lee, S. S.; Lico, R.; Lisakov, M. M.; Lobanov, A. P.; Petrov, L.; Sohn, B. W.; Sokolovsky, K. V.; Voitsik, P. A.; Zensus, J. A.; Tingay, S.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Understanding the formation of relativistic jets in active galactic nuclei remains an elusive problem 1 .This is partly because observational tests of jet formation models suffer from the limited angular resolution of ground-based very-long-baseline interferometry that has thus far been able to probe the structure of the jet acceleration and collimation region in only two sources 2,3 . Here, we report observations of 3C84 (NGC 1275)-the central galaxy of the Perseus cluster-made with an interferometric array including the orbiting radio telescope of the RadioAstron 4 mission. The data transversely resolve the edge-brightened jet in 3C84 only 30 μas from the core, which is ten times closer to the central engine than was possible in previous ground-based observations 5 and allows us to measure the jet collimation profile from ~102 to ~104 gravitational radii (r g) from the black hole. The previously found 5, almost cylindrical jet profile on scales larger than a few thousand r g is seen to continue at least down to a few hundred r g from the black hole, and we find a broad jet with a transverse radius of â‰250 r g at only 350 r g from the core. This implies that either the bright outer jet layer goes through a very rapid lateral expansion on scales â‰102 r g or it is launched from the accretion disk.