RadioAstron Space VLBI Imaging of the Jet in M87. I. Detection of High Brightness Temperature at 22 GHz

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A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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2023-07-01
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en
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Astrophysical Journal, Volume 952, issue 1
Abstract
We present results from the first 22 GHz space very long baseline interferometric (VLBI) imaging observations of M87 by RadioAstron. As a part of the Nearby AGN Key Science Program, the source was observed in 2014 February at 22 GHz with 21 ground stations, reaching projected (u, v) spacings up to ∼11 Gλ. The imaging experiment was complemented by snapshot RadioAstron data of M87 obtained during 2013-2016 from the AGN Survey Key Science Program. Their longest baselines extend up to ∼25 Gλ. For all of these measurements, fringes are detected only up to ∼2.8 Earth diameter or ∼3 Gλ baseline lengths, resulting in a new image with angular resolution of ∼150 μas or ∼20 Schwarzschild radii spatial resolution. The new image not only shows edge-brightened jet and counterjet structures down to submilliarcsecond scales but also clearly resolves the VLBI core region. While the overall size of the core is comparable to those reported in the literature, the ground-space fringe detection and slightly superresolved RadioAstron image suggest the presence of substructures in the nucleus, whose minimum brightness temperature exceeds T B , min ∼ 10 12 K. It is challenging to explain the origin of this record-high T B , min value for M87 by pure Doppler boosting effect with a simple conical jet geometry and known jet speed. Therefore, this can be evidence for more extreme Doppler boosting due to a blazar-like small jet viewing angle or highly efficient particle acceleration processes occurring already at the base of the outflow.
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Funding Information: We thank the anonymous referee for providing helpful comments, which improved the paper and discussions, and Eduardo Ros for a careful review of the manuscript and constructive suggestions. J.Y.K. was supported for this research by the National Research Foundation of Korea (NRF) funded by the Korean government (Ministry of Science and ICT; grant No. 2022R1C1C1005255). T.S. was funded by the Academy of Finland projects 274477 and 315721. E.V.K., Y.Y.K., and A.P.L. were supported by the Russian Science Foundation project 20-62-46021. S.-S.L. was supported by the NRF grant funded by the government of Korea (MIST) (2020R1A2C2009003). B.W.S. is grateful for the support by the NRF funded by the Ministry of Science and ICT of Korea (NRF-2020K1A3A1A78114060). The RadioAstron project was led by the Astro Space Center of the Lebedev Physical Institute of the Russian Academy of Sciences and the Lavochkin Scientific and Production Association under a contract with the Russian Federal Space Agency, in collaboration with partner organizations in Russia and other countries. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The European VLBI Network is a joint facility of independent European, African, Asian, and North American radio astronomy institutes. This research is based on observations correlated at the Bonn Correlator, jointly operated by the Max Planck Institute for Radio Astronomy (MPIfR), and the Federal Agency for Cartography and Geodesy (BKG). The Australia Telescope Compact Array and Mopra telescope are part of the Australia Telescope National Facility ( https://ror.org/05qajvd42 ), which is funded by the Australian Government for operation as a National Facility managed by CSIRO. Funding Information: We thank the anonymous referee for providing helpful comments, which improved the paper and discussions, and Eduardo Ros for a careful review of the manuscript and constructive suggestions. J.Y.K. was supported for this research by the National Research Foundation of Korea (NRF) funded by the Korean government (Ministry of Science and ICT; grant No. 2022R1C1C1005255). T.S. was funded by the Academy of Finland projects 274477 and 315721. E.V.K., Y.Y.K., and A.P.L. were supported by the Russian Science Foundation project 20-62-46021. S.-S.L. was supported by the NRF grant funded by the government of Korea (MIST) (2020R1A2C2009003). B.W.S. is grateful for the support by the NRF funded by the Ministry of Science and ICT of Korea (NRF-2020K1A3A1A78114060). The RadioAstron project was led by the Astro Space Center of the Lebedev Physical Institute of the Russian Academy of Sciences and the Lavochkin Scientific and Production Association under a contract with the Russian Federal Space Agency, in collaboration with partner organizations in Russia and other countries. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement byAssociated Universities, Inc. The European VLBI Network is a joint facility of independent European, African, Asian, and North American radio astronomy institutes. This research is based on observations correlated at the Bonn Correlator, jointly operated by the Max Planck Institute for Radio Astronomy (MPIfR), and the Federal Agency for Cartography and Geodesy (BKG). The Australia Telescope Compact Array and Mopra telescope are part of the Australia Telescope National Facility (https://ror.org/05qajvd42), which is funded by the Australian Government for operation as a National Facility managed by CSIRO. Publisher Copyright: © 2023. The Author(s). Published by the American Astronomical Society.
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Kim, J Y, Savolainen, T, Voitsik, P, Kravchenko, E V, Lisakov, M M, Kovalev, Y Y, Müller, H, Lobanov, A P, Sokolovsky, K V, Bruni, G, Edwards, P G, Reynolds, C, Bach, U, Gurvits, L I, Krichbaum, T P, Hada, K, Giroletti, M, Orienti, M, Anderson, J M, Lee, S S, Sohn, B W & Zensus, J A 2023, ' RadioAstron Space VLBI Imaging of the Jet in M87. I. Detection of High Brightness Temperature at 22 GHz ', Astrophysical Journal, vol. 952, no. 1, 34 . https://doi.org/10.3847/1538-4357/accf17