分类： 天文学 >> 天文学 提交时间： 2023-02-19
Leonid I. Gurvits
Sándor Frey
Máté Krezinger
Oleg Titov
Tao An
Yingkang Zhang
Alexander G. Polnarev
Krisztina É. Gabányi
Krisztina Perger
Alexey Melnikov
摘要： We present and briefly discuss results of several studies of the source J2102+6015 with tentatively defined redshift z=4:575 which demonstrates unusual properties in imaging and astrometric VLBI observations. Its properties might be considered as indications on the supermassive black hole binary which can be considered as a so far rare example of a high-redshift source of known electromagnetic and, possibly, predictable gravitational wave emissions.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Oleg Titov
Sandor Frey
Alexei Melnikov
Fengchun Shu
Bo Xia
Javier Gonzalez
Belen Tercero
Leonid Gurvits
Aletha de Witt
Jamie McCallum
Mikhail Kharinov
Vladimir Zimovsky
Mate Krezinger
摘要： Radio-loud quasars at high redshift (z > 4) are rare objects in the Universe and rarely observed with Very Long Baseline Interferometry (VLBI). But some of them have flux density sufficiently high for monitoring of their apparent position. The instability of the astrometric positions could be linked to the astrophysical process in the jetted active galactic nuclei in the early Universe. Regular observations of the high-redshift quasars are used for estimating their apparent proper motion over several years. We have undertaken regular VLBI observations of several high-redshift quasars at 2.3 GHz (S band) and 8.4 GHz (X band) with a network of five radio telescopes: 40-m Yebes (Spain), 25-m Sheshan (China), and three 32-m telescopes of the Quasar VLBI Network (Russia) -- Svetloe, Zelenchukskaya, and Badary. Additional facilities joined this network occasionally. The sources have also been observed in three sessions with the European VLBI Network (EVN) in 2018--2019 and one Long Baseline Array (LBA) experiment in 2018. In addition, several experiments conducted with the Very Long Baseline Array (VLBA) in 2017--2018were used to improve the time sampling and the statistics. Based on these 37 astrometric VLBI experiments between 2017 and 2021, we estimated the apparent proper motions of four quasars: 0901+697, 1428+422, 1508+572, and 2101+600.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yingkang Zhang
Tao An
Sándor Frey
Xiaolong Yang
Máté Krezinger
Oleg Titov
Alexey Melnikov
Pablo de Vicente
Fengchun Shu
Ailing Wang
摘要： Jets of high-redshift active galactic nuclei (AGNs) can be used to directly probe the activity of the black holes in the early Universe. Radio sources with jets misaligned with respect to the line of sight are expected to dominate the high-redshift AGN population. In this paper, we present the high-resolution imaging results of a z=4.57 AGN J2102+6015 by analyzing its multi-epoch dual-frequency very long baseline interferometry (VLBI) data. The 8.4-GHz VLBI images reveal two major features along the east-west direction separated by $\sim$ 10 milli-arcsec (mas). From the spectral index map, both features show flat/inverted spectra. The separation between the two features remains almost unchanged over an observation period of $\sim$ 13 years, placing an upper limit of the separation speed as about 0.04 mas year$^{-1}$. Previous studies have classified the source as a GHz-peaked spectrum quasar. Our results indicate that J2102+6015 is most likely a young, compact symmetric object rather than a blazar-type core-jet source.
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