Magnetic field strengths of the synchrotron self-absorption region in the jet of CTA 102 during radio flares

Creators: Kim, Sang-Hyun; Lee, Sang-Sung; Lee, Jee Won; Hodgson, Jeffrey A.; Kang, Sincheol; Algaba, Juan-Carlos; Kim, Jae-Young; Hodges, Mark; Agudo, Ivan; Fuentes, Antonio; Escudero, Juan; Myserlis, Ioannis; Traianou, Efthalia; Lähteenmäki, Anne; Tornikoski, Merja; Tammi, Joni; Ramakrishnan, Venkatessh; Järvelä, Emilia

Abstract

CTA 102 is a blazar implying that its relativistic jet points towards Earth and emits synchrotron radiation produced by energetic particles gyrating in the magnetic field. This study aims to figure out the physical origins of radio flares in the jet, including the connection between the magnetic field and the radio flares. The data set in the range of 2.6–343.5 GHz was collected over a period of ∼5.5 yr (2012 November 20–2018 September 23). During the data collection period, seven flares at 15 GHz with a range of the variability time-scale of roughly 76–227 d were detected. The quasi-simultaneous radio data were used to investigate the synchrotron spectrum of the source. We found that the synchrotron radiation is self-absorbed. The turnover frequency and the peak flux density of the synchrotron self-absorption (SSA) spectra are in the ranges of ∼42–172 GHz and ∼0.9–10.2 Jy, respectively. From the SSA spectra, we derived the SSA magnetic field strengths to be ∼9.20, ∼12.28, and ∼50.97 mG on 2013 December 24, 2014 February 28, and 2018 January 13, respectively. We also derived the equipartition magnetic field strengths to be in the range of ∼24–109 mG. The equipartition magnetic field strengths are larger than the SSA magnetic field strengths in most cases, which indicates that particle energy mainly dominates in the jet. Our results suggest that the flares in the jet of CTA 102 originated due to particle acceleration. We propose the possible mechanisms of particle acceleration.

Additional Information

© 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model) Accepted 2021 November 25. Received 2021 November 25; in original form 2021 May 12. We thank the anonymous referee for valuable comments and suggestions that helped to improve the paper. We are grateful to the staff of the KVN who helped to operate the array and to correlate the data. The KVN is a facility operated by the KASI (Korea Astronomy and Space Science Institute). The KVN observations and correlations are supported through the high-speed network connections among the KVN sites provided by the KREONET (Korea Research Environment Open NETwork), which is managed and operated by the KISTI (Korea Institute of Science and Technology Information). This research has made use of data from the OVRO 40-m monitoring programme that was supported in part by NASA grants NNX08AW31G, NNX11A043G, and NNX14AQ89G, and NSF grants AST-0808050 and AST-1109911, and private funding from Caltech and the MPIfR. This publication makes use of data obtained at the Metsähovi Radio Observatory, operated by Aalto University in Finland. IA acknowledges financial support from the Spanish 'Ministerio de Ciencia e Innovación' (MCINN) through the 'Center of Excellence Severo Ochoa' award for the Instituto de Astrofísica de Andalucía-CSIC (SEV-2017-0709). Acquisition and reduction of the MAPCAT data was supported in part by MICINN through grants AYA2016-80889-P and PID2019-107847RB-C44. The POLAMI observations were carried out at the IRAM 30m Telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). The Submillimetre Array is a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics and is funded by the Smithsonian Institution and the Academia Sinica. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2011.0.00001.CAL. ALMA is a partnership of ESO (representing its member states), NSF (USA), and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI(Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. This research has made use of data from the MOJAVE data base that is maintained by the MOJAVE team (Lister et al. 2018). This study makes use of VLBA data from the VLBA-BU Blazar Monitoring Program (BEAM-ME and VLBA-BU-BLAZAR; http://www.bu.edu/blazars/BEAM-ME.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 work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MIST) (2020R1A2C2009003). DATA AVAILABILITY. The data underlying this article will be shared on reasonable request to the corresponding author. And the SMA data are available in Submillimeter Calibrator List at http://sma1.sma.hawaii.edu/callist/callist.html; for questions regarding their availability, please contact Mark Gurwell (mgurwell@cfa.harvard.edu). The ALMA data are available in ALMA Calibrator Source Catalogue at https://almascience.eso.org/sc/. The VLBA 15 GHz data collected by the MOJAVE programme are available at https://www.physics.purdue.edu/MOJAVE/. The VLBA 43 GHz data collected by the VLBA-BU-BLAZAR monitoring programme are available at https://www.bu.edu/blazars/VLBAproject.html.

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