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...
| Main Authors: | , , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2024-01-01
|
| Series: | The Astrophysical Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/1538-4357/ad2c91 |
| _version_ | 1827302046013849600 |
|---|---|
| author | Jee Won Lee Sang-Sung Lee Jeffrey Hodgson Juan-Carlos Algaba Sanghyun Kim Whee Yeon Cheong Hyeon-Woo Jeong Sincheol Kang |
| author_facet | Jee Won Lee Sang-Sung Lee Jeffrey Hodgson Juan-Carlos Algaba Sanghyun Kim Whee Yeon Cheong Hyeon-Woo Jeong Sincheol Kang |
| author_sort | Jee Won Lee |
| collection | DOAJ |
| 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. |
| first_indexed | 2024-04-24T16:36:29Z |
| format | Article |
| id | doaj.art-e2862ac6e4264347a76c70c75aa67ba1 |
| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-04-24T16:36:29Z |
| publishDate | 2024-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-e2862ac6e4264347a76c70c75aa67ba12024-03-29T15:26:31ZengIOP PublishingThe Astrophysical Journal1538-43572024-01-01964217610.3847/1538-4357/ad2c91A Study of the Radio Spectrum of Mrk 421Jee Won Lee0https://orcid.org/0000-0003-2147-0290Sang-Sung Lee1https://orcid.org/0000-0002-6269-594XJeffrey Hodgson2https://orcid.org/0000-0001-6094-9291Juan-Carlos Algaba3https://orcid.org/0000-0001-6993-1696Sanghyun Kim4https://orcid.org/0000-0001-7556-8504Whee Yeon Cheong5https://orcid.org/0009-0002-1871-5824Hyeon-Woo Jeong6https://orcid.org/0009-0005-7629-8450Sincheol Kang7https://orcid.org/0000-0002-0112-4836Korea Astronomy and Space Science Institute , 776 Daedeok-daero, Yuseong-gu, Daejeon 34055, Republic of Korea ; sslee@kasi.re.krKorea Astronomy and Space Science Institute , 776 Daedeok-daero, Yuseong-gu, Daejeon 34055, Republic of Korea ; sslee@kasi.re.kr; University of Science and Technology , 217 Gajeong-ro, Yuseong-gu, Daejeon 34113, Republic of KoreaDepartment of Physics and Astronomy, Sejong University , 209 Neungdong-ro, Gwangjin-gu, Seoul, Republic of KoreaDepartment of Physics, Faculty of Science, Universiti Malaya , 50603 Kuala Lumpur, MalaysiaKorea Astronomy and Space Science Institute , 776 Daedeok-daero, Yuseong-gu, Daejeon 34055, Republic of Korea ; sslee@kasi.re.kr; University of Science and Technology , 217 Gajeong-ro, Yuseong-gu, Daejeon 34113, Republic of KoreaKorea Astronomy and Space Science Institute , 776 Daedeok-daero, Yuseong-gu, Daejeon 34055, Republic of Korea ; sslee@kasi.re.kr; University of Science and Technology , 217 Gajeong-ro, Yuseong-gu, Daejeon 34113, Republic of KoreaKorea Astronomy and Space Science Institute , 776 Daedeok-daero, Yuseong-gu, Daejeon 34055, Republic of Korea ; sslee@kasi.re.kr; University of Science and Technology , 217 Gajeong-ro, Yuseong-gu, Daejeon 34113, Republic of KoreaKorea Astronomy and Space Science Institute , 776 Daedeok-daero, Yuseong-gu, Daejeon 34055, Republic of Korea ; sslee@kasi.re.krWe 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.https://doi.org/10.3847/1538-4357/ad2c91Markarian galaxiesBlazarsBL Lacertae objectsActive galaxiesRelativistic jets |
| spellingShingle | Jee Won Lee Sang-Sung Lee Jeffrey Hodgson Juan-Carlos Algaba Sanghyun Kim Whee Yeon Cheong Hyeon-Woo Jeong Sincheol Kang A Study of the Radio Spectrum of Mrk 421 The Astrophysical Journal Markarian galaxies Blazars BL Lacertae objects Active galaxies Relativistic jets |
| title | 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_short | A Study of the Radio Spectrum of Mrk 421 |
| title_sort | study of the radio spectrum of mrk 421 |
| topic | Markarian galaxies Blazars BL Lacertae objects Active galaxies Relativistic jets |
| url | https://doi.org/10.3847/1538-4357/ad2c91 |
| work_keys_str_mv | AT jeewonlee astudyoftheradiospectrumofmrk421 AT sangsunglee astudyoftheradiospectrumofmrk421 AT jeffreyhodgson astudyoftheradiospectrumofmrk421 AT juancarlosalgaba astudyoftheradiospectrumofmrk421 AT sanghyunkim astudyoftheradiospectrumofmrk421 AT wheeyeoncheong astudyoftheradiospectrumofmrk421 AT hyeonwoojeong astudyoftheradiospectrumofmrk421 AT sincheolkang astudyoftheradiospectrumofmrk421 AT jeewonlee studyoftheradiospectrumofmrk421 AT sangsunglee studyoftheradiospectrumofmrk421 AT jeffreyhodgson studyoftheradiospectrumofmrk421 AT juancarlosalgaba studyoftheradiospectrumofmrk421 AT sanghyunkim studyoftheradiospectrumofmrk421 AT wheeyeoncheong studyoftheradiospectrumofmrk421 AT hyeonwoojeong studyoftheradiospectrumofmrk421 AT sincheolkang studyoftheradiospectrumofmrk421 |