Multiband optical variability on diverse timescales of the blazar Ton 599 from 2011 to 2023

Context. We analyze the optical variability of the flat-spectrum radio quasar (FSRQ) Ton 599 using BVRI photometry from the Whole Earth Blazar Telescope (WEBT) collaboration (2011–2023), complemented by photometric and spectroscopic data from the Steward Observatory monitoring program. Aims. We aim to characterize short- and long-term optical variability – including flux distributions, intranight changes, color evolution, and spectra – to constrain physical parameters and processes in the central engine of this active galactic nucleus (AGN). Methods. We tested flux distributions in each filter against normal and log-normal models and explored the root mean square (RMS)–flux relation. We derived power spectral densities (PSDs) to assess red-noise behavior. We quantified intranight variability using a χ 2 test and fractional variability. From variability timescales, we estimated the emitting region size and magnetic field. Long-term variability was studied by segmenting the light curve into 12 intervals and analyzing flux statistics. For multi-filter flares, we computed spectral slopes, redshift-corrected fluxes, and monochromatic luminosities. Color-magnitude and color-time diagrams traced color evolution over different flux regimes and timescales. From low-flux spectra, we measured Mg II line properties (correcting for Fe II) to estimate the black hole mass via single-epoch scaling. Results. During the monitoring period, Ton 599 showed strong optical variability. Log-normal distributions fit the fluxes better than normal ones, and all bands display a positive RMS–flux relation. The PSDs follow red-noise trends. Intranight variability is detected, with derived timescales constraining the emission region and magnetic field. The R band reaches a peak flux of 23.5 mJy, corresponding to a monochromatic luminosity of log( νL ν ) = 48.48 [erg s −1 ]. Color-magnitude diagrams reveal a redder-when-brighter trend at low fluxes (thermal dominance), achromatic behavior at intermediate levels (possibly due to jet orientation changes), and a bluer-when-brighter trend at high fluxes (synchrotron dominance). While long-term color changes are modest, short-term variations are significant, with a negative correlation between the amplitude of color changes and the average flux. The estimated supermassive black hole mass is on the order of 10 8 M ⊙ , which is in agreement with previous estimates. Conclusions. Our results underscore the complexity of blazar variability, pointing to multiple emission processes at work. The joint photometric and spectroscopic approach constrains key physical parameters and deepens our understanding of the blazar central engine.

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Publication Details

Journal
Astronomy and Astrophysics
Published
2025-10-03
DOI
https://doi.org/10.1051/0004-6361/202555986
Citations
2
Primary Topic
Astrophysics and Cosmic Phenomena
Type
article
Field-Weighted Citation Impact
3.74
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article

Multiband optical variability on diverse timescales of the blazar Ton 599 from 2011 to 2023

B. Mihov, Alessandro Marchini, L. Kunkel, A. Strigachev et al.
2 citations
Astronomy and Astrophysics
Astrophysics and Cosmic Phenomena
3.74
article

Multiband optical variability on diverse timescales of the blazar Ton 599 from 2011 to 2023

B. Mihov, Alessandro Marchini, L. Kunkel, A. Strigachev, M. I. Carnerero, Ekaterina V. Shishkina, A. A. Vasilyev, Alok C. Gupta, A. Takey, Daniel Morcuende, А. С. Москвитин, A. Sota, R. Steineke, А. В. Жовтан, L. V. Larionova, M. Stojanović, V. Bozhilov, Paul S. Smith, T. Pursimo, S. O. Kurtanidze, M. G. Nikolashvili, V. M. Larionov, A. Shokry, Е. Г. Ларионова, Yu. V. Troitskaya, С. С. Савченко, W. Chen, R. Z. Ivanidze, T. S. Grishina, I. Agudo, D. O. Mirzaqulov, G. Verna, D. A. Morozova, V. V. Vlasyuk, E. Zaharieva, J.R. Webb, C. Lorey, I. S. Troitskiy, M. Villata, V. A. Hagen‐Thorn, G. Bonnoli, O. M. Kurtanidze, L. Slavcheva-Mihova, M. D. Jovanović, A. Valcheva, Г. А. Борман, D. Carosati, C. M. Raiteri, O. I. Spiridonova, D. Elsäesser, An-Li Tsai, Sh. A. Ehgamberdiev, Z. R. Weaver, Jonathan A. Ledermann, Maša Lakićević, O. Vince, Pankaj Kushwaha, V. Casanova, M. Minev, A. Scherbantin, J. A. Acosta‐Pulido, R. Bachev, David Reinhart, M. Feige, G. Damljanović, A. P. Marscher, S.G. Jorstad, Luka Č. Popović, E. N. Kopatskaya, K.F. Schoch, H. C. Lin, J. Kovǎ cević-Doǰ cinović
article en
2 citations

Abstract

Context. We analyze the optical variability of the flat-spectrum radio quasar (FSRQ) Ton 599 using BVRI photometry from the Whole Earth Blazar Telescope (WEBT) collaboration (2011–2023), complemented by photometric and spectroscopic data from the Steward Observatory monitoring program. Aims. We aim to characterize short- and long-term optical variability – including flux distributions, intranight changes, color evolution, and spectra – to constrain physical parameters and processes in the central engine of this active galactic nucleus (AGN). Methods. We tested flux distributions in each filter against normal and log-normal models and explored the root mean square (RMS)–flux relation. We derived power spectral densities (PSDs) to assess red-noise behavior. We quantified intranight variability using a χ 2 test and fractional variability. From variability timescales, we estimated the emitting region size and magnetic field. Long-term variability was studied by segmenting the light curve into 12 intervals and analyzing flux statistics. For multi-filter flares, we computed spectral slopes, redshift-corrected fluxes, and monochromatic luminosities. Color-magnitude and color-time diagrams traced color evolution over different flux regimes and timescales. From low-flux spectra, we measured Mg II line properties (correcting for Fe II) to estimate the black hole mass via single-epoch scaling. Results. During the monitoring period, Ton 599 showed strong optical variability. Log-normal distributions fit the fluxes better than normal ones, and all bands display a positive RMS–flux relation. The PSDs follow red-noise trends. Intranight variability is detected, with derived timescales constraining the emission region and magnetic field. The R band reaches a peak flux of 23.5 mJy, corresponding to a monochromatic luminosity of log( νL ν ) = 48.48 [erg s −1 ]. Color-magnitude diagrams reveal a redder-when-brighter trend at low fluxes (thermal dominance), achromatic behavior at intermediate levels (possibly due to jet orientation changes), and a bluer-when-brighter trend at high fluxes (synchrotron dominance). While long-term color changes are modest, short-term variations are significant, with a negative correlation between the amplitude of color changes and the average flux. The estimated supermassive black hole mass is on the order of 10 8 M ⊙ , which is in agreement with previous estimates. Conclusions. Our results underscore the complexity of blazar variability, pointing to multiple emission processes at work. The joint photometric and spectroscopic approach constrains key physical parameters and deepens our understanding of the blazar central engine.

Astronomy and AstrophysicsVol. 703
Boston University (US), Federal Foreign Office (DE), University of Arizona (US), Universidad de La Laguna (ES), Indian Institute of Science Education and Research Mohali (IN), St Petersburg University (RU), Florida International University (US), TU Dortmund University (DE), National Central University (TW), Heidelberg University (DE), Shanghai Astronomical Observatory (CN), Special Astrophysical Observatory (RU), Istituto Nazionale di Fisica Nucleare, Galileo Galilei Institute for Theoretical Physics (IT), Xinjiang Astronomical Observatory (CN), Pulkovo Observatory (RU), Brera Astronomical Observatory (IT), Evgeni Kharadze Georgian National Astrophysical Observatory (GE), Aryabhatta Research Institute of Observational Sciences (IN), Guangzhou University (CN), University of Belgrade (RS), Ulugh Beg Astronomical Institute (UZ), Osservatorio Astrofisico di Torino (IT), National Research Institute of Astronomy and Geophysics (EG), NIU Observatory (US), Institute of Astronomy and National Astronomical Observatory (BG), Institute of Astronomy (RU), Center for Astrophysics Harvard & Smithsonian (US), Nordic Optical Telescope (ES), Instituto de Astrofísica de Canarias (ES), Astronomical Institute of the Slovak Academy of Sciences (SK), École Polytechnique de Thiès (SN), Astronomical Observatory (RS), Max Planck Institute for Radio Astronomy (DE), Instituto de Astrofísica de Andalucía (ES), Telescopio Nazionale Galileo (ES), Crimean Astrophysical Observatory (UA), National University of Uzbekistan (UZ), Sofia University "St. Kliment Ohridski" (BG), University of Colorado Denver (US)
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Astrophysics and Cosmic Phenomena
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