Optical Flux and Spectral Variability of BL Lacertae during Its Historical High Outburst in 2020
BL Lacertae underwent a series of historical high flux activity over a year from 2020 August in the optical to VHE γ -rays. In this paper, we report on optical flux and spectral variability of the first historical maxima outburst event during October–November in the g , r , and i bands with the 1.26...
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| Format: | Article |
| Language: | English |
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IOP Publishing
2023-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/aca801 |
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| author | Nibedita Kalita Yuhai Yuan Minfeng Gu Junhui Fan Yosuke Mizuno Peng Jiang Alok C. Gupta Hongyan Zhou Xiang Pan Anton A. Strigachev Rumen S. Bachev Lang Cui |
| author_facet | Nibedita Kalita Yuhai Yuan Minfeng Gu Junhui Fan Yosuke Mizuno Peng Jiang Alok C. Gupta Hongyan Zhou Xiang Pan Anton A. Strigachev Rumen S. Bachev Lang Cui |
| author_sort | Nibedita Kalita |
| collection | DOAJ |
| description | BL Lacertae underwent a series of historical high flux activity over a year from 2020 August in the optical to VHE γ -rays. In this paper, we report on optical flux and spectral variability of the first historical maxima outburst event during October–November in the g , r , and i bands with the 1.26 m telescope at the Xinglong Observatory, China. We detected significant intranight variations with amplitude rising up to ∼30%, where the fastest variability timescale was found to be a few tens of minutes, giving an emitting region size of the order 10 ^−3 pc, which corresponds to ∼100 Schwarzschild radius of the central black hole, likely coming from some jet mini-structures. Unlike on the intranight timescale, a clear frequency-dependent pattern along symmetric timescales (∼11 days) of flux variation is detected on a long timescale. The spectral evolution was predominated by flattening of the spectra with increasing brightness i.e., a bluer-when-brighter trend in 96% of the cases. On the night before the outburst peak, the color indices shown in a color–magnitude diagram, clustered into two distinct branches, within a period of ∼6 hr, which is connected to a hard-soft-hard spectral evolution trend extracted from time-resolved spectra. To the best of our knowledge, such a trend has never been seen in BL Lac or any other blazars before. The results obtained in this study can be explained in the context of shock-induced particle acceleration or magnetic reconnection in the jet where turbulent processes most likely resulted in the asymmetric flux variation on a nightly timescale. |
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| id | doaj.art-46a3e90b89854ad79df0b8c0399682e7 |
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| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-12T04:44:49Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
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| series | The Astrophysical Journal |
| spelling | doaj.art-46a3e90b89854ad79df0b8c0399682e72023-09-03T09:29:26ZengIOP PublishingThe Astrophysical Journal1538-43572023-01-01943213510.3847/1538-4357/aca801Optical Flux and Spectral Variability of BL Lacertae during Its Historical High Outburst in 2020Nibedita Kalita0https://orcid.org/0000-0002-9323-4150Yuhai Yuan1https://orcid.org/0000-0001-7833-2468Minfeng Gu2https://orcid.org/0000-0002-4455-6946Junhui Fan3https://orcid.org/0000-0002-5929-0968Yosuke Mizuno4https://orcid.org/0000-0002-8131-6730Peng Jiang5Alok C. Gupta6https://orcid.org/0000-0002-9331-4388Hongyan Zhou7Xiang Pan8https://orcid.org/0000-0002-6565-2339Anton A. Strigachev9Rumen S. Bachev10https://orcid.org/0000-0002-0766-864XLang Cui11https://orcid.org/0000-0003-0721-5509Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences , 80 Nandan Road, Shanghai 200030, People’s Republic of China ; nibeditaklt1@gmail.com; Key Laboratory for Polar Science, MNR, Polar Research Institute of China , 451 Jinqiao Road, Shanghai 200135, People’s Republic of ChinaCenter for Astrophysics, Guangzhou University , Guangzhou 510006, People’s Republic of China; Astronomy Science and Technology Research Laboratory, Department of Education of Guangdong Province , Guangzhou 510006, People’s Republic of ChinaKey Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences , 80 Nandan Road, Shanghai 200030, People’s Republic of China ; nibeditaklt1@gmail.comCenter for Astrophysics, Guangzhou University , Guangzhou 510006, People’s Republic of China; Astronomy Science and Technology Research Laboratory, Department of Education of Guangdong Province , Guangzhou 510006, People’s Republic of ChinaTsung-Dao Lee Institute, Shanghai Jiao Tong University , 520 Shengrong Road, Shanghai, 201210, People’s Republic of China; School of Physics and Astronomy, Shanghai Jiao Tong University , 800 Dongchuan Road, Shanghai, 200240, People’s Republic of ChinaKey Laboratory for Polar Science, MNR, Polar Research Institute of China , 451 Jinqiao Road, Shanghai 200135, People’s Republic of ChinaKey Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences , 80 Nandan Road, Shanghai 200030, People’s Republic of China ; nibeditaklt1@gmail.com; Aryabhatta Research Institute of Observational Sciences (ARIES) , Manora Peak, Nainital, 263001, IndiaKey Laboratory for Polar Science, MNR, Polar Research Institute of China , 451 Jinqiao Road, Shanghai 200135, People’s Republic of ChinaKey Laboratory for Polar Science, MNR, Polar Research Institute of China , 451 Jinqiao Road, Shanghai 200135, People’s Republic of ChinaInstitute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences , 72 Tsarigradsko shosse Boulevard, 1784 Sofia, BulgariaInstitute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences , 72 Tsarigradsko shosse Boulevard, 1784 Sofia, BulgariaXinjiang Astronomical Observatory, Chinese Academy of Sciences , 150 Science 1-Street, 830011 Urumqi, People’s Republic of ChinaBL Lacertae underwent a series of historical high flux activity over a year from 2020 August in the optical to VHE γ -rays. In this paper, we report on optical flux and spectral variability of the first historical maxima outburst event during October–November in the g , r , and i bands with the 1.26 m telescope at the Xinglong Observatory, China. We detected significant intranight variations with amplitude rising up to ∼30%, where the fastest variability timescale was found to be a few tens of minutes, giving an emitting region size of the order 10 ^−3 pc, which corresponds to ∼100 Schwarzschild radius of the central black hole, likely coming from some jet mini-structures. Unlike on the intranight timescale, a clear frequency-dependent pattern along symmetric timescales (∼11 days) of flux variation is detected on a long timescale. The spectral evolution was predominated by flattening of the spectra with increasing brightness i.e., a bluer-when-brighter trend in 96% of the cases. On the night before the outburst peak, the color indices shown in a color–magnitude diagram, clustered into two distinct branches, within a period of ∼6 hr, which is connected to a hard-soft-hard spectral evolution trend extracted from time-resolved spectra. To the best of our knowledge, such a trend has never been seen in BL Lac or any other blazars before. The results obtained in this study can be explained in the context of shock-induced particle acceleration or magnetic reconnection in the jet where turbulent processes most likely resulted in the asymmetric flux variation on a nightly timescale.https://doi.org/10.3847/1538-4357/aca801Active galactic nucleiBlazars |
| spellingShingle | Nibedita Kalita Yuhai Yuan Minfeng Gu Junhui Fan Yosuke Mizuno Peng Jiang Alok C. Gupta Hongyan Zhou Xiang Pan Anton A. Strigachev Rumen S. Bachev Lang Cui Optical Flux and Spectral Variability of BL Lacertae during Its Historical High Outburst in 2020 The Astrophysical Journal Active galactic nuclei Blazars |
| title | Optical Flux and Spectral Variability of BL Lacertae during Its Historical High Outburst in 2020 |
| title_full | Optical Flux and Spectral Variability of BL Lacertae during Its Historical High Outburst in 2020 |
| title_fullStr | Optical Flux and Spectral Variability of BL Lacertae during Its Historical High Outburst in 2020 |
| title_full_unstemmed | Optical Flux and Spectral Variability of BL Lacertae during Its Historical High Outburst in 2020 |
| title_short | Optical Flux and Spectral Variability of BL Lacertae during Its Historical High Outburst in 2020 |
| title_sort | optical flux and spectral variability of bl lacertae during its historical high outburst in 2020 |
| topic | Active galactic nuclei Blazars |
| url | https://doi.org/10.3847/1538-4357/aca801 |
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