Identifying changing jets through their radio variability
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A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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en
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12
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Astronomy & Astrophysics, Volume 654
Abstract
Context. Supermassive black holes can launch highly relativistic jets with velocities reaching Lorentz factors of as high as Gamma > 50. How the jets accelerate to such high velocities and where along the jet they reach terminal velocity are open questions that are tightly linked to their structure as well as their launching and dissipation mechanisms. Aims. Changes in the beaming factor along the jets could potentially reveal jet acceleration, deceleration, or bending. We aim to (1) quantify the relativistic effects in multiple radio frequencies and (2) study possible jet velocity-viewing angle variations at parsec scales. Methods. We used the state-of-the-art code Magnetron to model light curves from the University of Michigan Radio Observatory and the Metsahovi Radio Observatory's monitoring programs in five frequencies covering about 25 years of observations in the 4.8 to 37 GHz range for 61 sources. We supplement our data set with high-frequency radio observations in the 100-340 GHz range from ALMA, CARMA, and SMA. For each frequency we estimate the Doppler factor which we use to quantify possible changes in the relativistic effects along the jets. Results. The majority of our sources do not show any statistically significant difference in their Doppler factor across frequencies. This is consistent with constant velocity in a conical jet structure, as expected at parsec scales. However, our analysis reveals 17 sources where relativistic beaming changes as a function of frequency. In the majority of cases, the Doppler factor increases towards lower frequencies. Only 1253-053 shows the opposite behavior. By exploring their jet properties we find that the jet of 0420-014 is likely bent across the 4.8-340 GHz range. For 0212+735, the jet is likely parabolic, and still accelerating in the 4.8-37 GHz range. We discuss possible interpretations for the trends found in the remaining sources.Description
Funding Information: Acknowledgements. The authors would like to thank Carolina Casadio, Dan Homan, and the anonymous referee for useful comments and discussions that helped improve this work. I.L. thanks the University of Crete for their hospitality during which the paper was written. T.H. was supported by the Academy of Finland projects 317383, 320085, and 322535. This research has made use of data from the MOJAVE database that is maintained by the MOJAVE team (Lister et al. 2018). This study makes use of 43 GHz VLBA data from the VLBA-BU Blazar Monitoring Program (VLBA-BU-BLAZAR; http://www. bu.edu/blazars/VLBAproject.html), funded by NASA through the Fermi Guest Investigator Program. The VLBA is an instrument of the National Radio Astronomy Observatory. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated by Associated Universities, Inc. This research has made use of data from the University of Michigan Radio Astronomy Observatory which has been supported by the University of Michigan and by a series of grants from the National Science Foundation, most recently AST-0607523, and from NASA Fermi G.I. grants NNX09AU16G, NNX10AP16G, NNX13AP18G, and NNX11AO13G. This publication makes use of data obtained at Metsähovi Radio Observatory, operated by Aalto University in Finland. The Submillimeter Array is a joint project between the Smithso-nian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics and is funded by the Smithsonian Institution and the Academia Sinica. Publisher Copyright: © 2021 EDP Sciences. All rights reserved.
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Liodakis, I, Hovatta, T, Aller, M F, Aller, H D, Gurwell, M A, Lähteenmäki, A & Tornikoski, M 2021, 'Identifying changing jets through their radio variability', Astronomy & Astrophysics, vol. 654, 169. https://doi.org/10.1051/0004-6361/202141053