Staff View: A Study of the Radio Spectrum of Mrk 421

A Study of the Radio Spectrum of Mrk 421

We present the results of a spectral analysis using simultaneous multifrequency (22, 43, 86, and 129 GHz) very long baseline interferometry (VLBI) observations of the Korean VLBI Network on BL Lac object, Markarian 421. The data we used were obtained from 2013 January to 2018 June. The light curves...

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Main Authors:	Lee, Jee Won, Lee, Sang-Sung, Hodgson, Jeffrey, Algaba, Juan Carlos, Kim, Sanghyun, Cheong, Whee Yeon, Jeong, Hyeon-Woo, Kang, Sincheol
Format:	Article
Published:	IOP Publishing Ltd 2024
Subjects:	QC Physics
Online Access:	http://eprints.um.edu.my/45369/ https://doi.org/10.3847/1538-4357/ad2c91
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spelling	my.um.eprints.453692024-10-15T02:23:30Z http://eprints.um.edu.my/45369/ A Study of the Radio Spectrum of Mrk 421 Lee, Jee Won Lee, Sang-Sung Hodgson, Jeffrey Algaba, Juan Carlos Kim, Sanghyun Cheong, Whee Yeon Jeong, Hyeon-Woo Kang, Sincheol QC Physics We present the results of a spectral analysis using simultaneous multifrequency (22, 43, 86, and 129 GHz) very long baseline interferometry (VLBI) observations of the Korean VLBI Network on BL Lac object, Markarian 421. The data we used were obtained from 2013 January to 2018 June. The light curves showed several flux enhancements with global decreases. To separate the variable and quiescent components in the multifrequency light curves for milliarcsecond-scale emission regions, we assumed that the quiescent radiation comes from the emission regions radiating constant optically thin synchrotron emissions (i.e., a minimum flux density with an optically thin spectral index). The quiescent spectrum determined from the multifrequency light curves was subtracted from the total CLEAN flux density, yielding a variable component in the flux that produces the time-dependent spectrum. We found that the observed spectra were flat at 22-43 GHz, and relatively steep at 43-86 GHz, whereas the quiescent-corrected spectra are sometimes quite different from the observed spectra (e.g., sometimes inverted at 22-43 GHz). The quiescent-corrected spectral indices were much more variable than the observed spectral indices. This spectral investigation implies that the quiescent-spectrum correction can significantly affect the multifrequency spectral index of variable compact radio sources such as blazars. Therefore, the synchrotron self-absorption B-field strength (B SSA) can be significantly affected because B SSA is proportional to the fifth power of turnover frequency. IOP Publishing Ltd 2024-04 Article PeerReviewed Lee, Jee Won and Lee, Sang-Sung and Hodgson, Jeffrey and Algaba, Juan Carlos and Kim, Sanghyun and Cheong, Whee Yeon and Jeong, Hyeon-Woo and Kang, Sincheol (2024) A Study of the Radio Spectrum of Mrk 421. Astrophysical Journal, 964 (2). p. 176. ISSN 0004-637X, DOI https://doi.org/10.3847/1538-4357/ad2c91 <https://doi.org/10.3847/1538-4357/ad2c91>. https://doi.org/10.3847/1538-4357/ad2c91 10.3847/1538-4357/ad2c91
institution	Universiti Malaya
building	UM Library
collection	Institutional Repository
continent	Asia
country	Malaysia
content_provider	Universiti Malaya
content_source	UM Research Repository
url_provider	http://eprints.um.edu.my/
topic	QC Physics
spellingShingle	QC Physics Lee, Jee Won Lee, Sang-Sung Hodgson, Jeffrey Algaba, Juan Carlos Kim, Sanghyun Cheong, Whee Yeon Jeong, Hyeon-Woo Kang, Sincheol A Study of the Radio Spectrum of Mrk 421
description	We present the results of a spectral analysis using simultaneous multifrequency (22, 43, 86, and 129 GHz) very long baseline interferometry (VLBI) observations of the Korean VLBI Network on BL Lac object, Markarian 421. The data we used were obtained from 2013 January to 2018 June. The light curves showed several flux enhancements with global decreases. To separate the variable and quiescent components in the multifrequency light curves for milliarcsecond-scale emission regions, we assumed that the quiescent radiation comes from the emission regions radiating constant optically thin synchrotron emissions (i.e., a minimum flux density with an optically thin spectral index). The quiescent spectrum determined from the multifrequency light curves was subtracted from the total CLEAN flux density, yielding a variable component in the flux that produces the time-dependent spectrum. We found that the observed spectra were flat at 22-43 GHz, and relatively steep at 43-86 GHz, whereas the quiescent-corrected spectra are sometimes quite different from the observed spectra (e.g., sometimes inverted at 22-43 GHz). The quiescent-corrected spectral indices were much more variable than the observed spectral indices. This spectral investigation implies that the quiescent-spectrum correction can significantly affect the multifrequency spectral index of variable compact radio sources such as blazars. Therefore, the synchrotron self-absorption B-field strength (B SSA) can be significantly affected because B SSA is proportional to the fifth power of turnover frequency.
format	Article
author	Lee, Jee Won Lee, Sang-Sung Hodgson, Jeffrey Algaba, Juan Carlos Kim, Sanghyun Cheong, Whee Yeon Jeong, Hyeon-Woo Kang, Sincheol
author_facet	Lee, Jee Won Lee, Sang-Sung Hodgson, Jeffrey Algaba, Juan Carlos Kim, Sanghyun Cheong, Whee Yeon Jeong, Hyeon-Woo Kang, Sincheol
author_sort	Lee, Jee Won
title	A Study of the Radio Spectrum of Mrk 421
title_short	A Study of the Radio Spectrum of Mrk 421
title_full	A Study of the Radio Spectrum of Mrk 421
title_fullStr	A Study of the Radio Spectrum of Mrk 421
title_full_unstemmed	A Study of the Radio Spectrum of Mrk 421
title_sort	study of the radio spectrum of mrk 421
publisher	IOP Publishing Ltd
publishDate	2024
url	http://eprints.um.edu.my/45369/ https://doi.org/10.3847/1538-4357/ad2c91
_version_	1814047548559589376
score	13.211869

A Study of the Radio Spectrum of Mrk 421

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