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

O. Vince, C. M. Raiteri, M. Villata, A. C. Gupta, J. Kovačević-Dojčinović, M. Lakićević, L. Č. Popović, P. Kushwaha, D. O. Mirzaqulov, S. A. Ehgamberdiev, D. Carosati, S. G. Jorstad, A. P. Marscher, Z. R. Weaver, J. R. Webb, P. S. Smith, W. P. Chen, A. Tsai, H. C. Lin, G. A. Borman, T. S. Grishina, V. A. Hagen-Thorn, E. N. Kopatskaya, E. G. Larionova, V. M. Larionov, L. V. Larionova, D. A. Morozova, S. S. Savchenko, I. S. Troitskiy, Y. V. Troitskaya, A. A. Vasilyev, A. V. Zhovtan, E. V. Shishkina, O. M. Kurtanidze, M. G. Nikolashvili, S. O. Kurtanidze, R. Ivanidze, J. A. Acosta-Pulido, M. I. Carnerero, G. Damljanović, M. Stojanovic, M. D. Jovanovic, V. V. Vlasyuk, O. I. Spiridonova, A. S. Moskvitin, T. Pursimo, D. Elsässer, M. Feige, L. Kunkel, J. Ledermann, D. Reinhart, A. Scherbantin, K. Schoch, R. Steineke, C. Lorey, I. Agudo, J. Escudero Pedrosa, F. J. Aceituno, G. Bonnoli, V. Casanova, D. Morcuende, A. Sota, V. Bozhilov, A. Valcheva, E. Zaharieva, M. Minev, A. Strigachev, R. Bachev, B. Mihov, L. Slavcheva-Mihova, A. C. Sadun, A. Takey, A. Shokry, M. A. El-Sadek, A. Marchiniand G. Verna

TL;DR

This study delivers a comprehensive, multi-year, multi-band optical variability analysis of the FSRQ Ton 599 using WEBT BVRI photometry (2011–2023) and Steward spectroscopy. By testing flux distributions, RMS–flux relations, and PSDs, it demonstrates log-normal long-term flux distributions with red-noise PSDs and detects intranight variability, constraining emission-region sizes and magnetic fields. The work further reveals intricate color evolution consistent with a two-component disk+jet model, and it estimates a central black hole mass of about $10^{8} M_ ext{sun}$ from Mg II lines, situating Ton 599 among highly variable, jet-dominated AGN. The results provide robust constraints on jet emission, particle acceleration, and disk–jet coupling across timescales, and emphasize a complex, location-dependent picture of variability in this blazar.

Abstract

(Shortened)Context: We analyze the optical variability of the FSRQ Ton 599 using BVRI photometry from the WEBT collaboration (2011-2023), complemented by photometric and spectroscopic data from the Steward Observatory.\\ Aims: 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.\\ Methods: We tested flux distributions in each filter against normal and log-normal, explored the RMS-flux relation and derived PSDs. 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, monochromatic luminosities and generated Color-magnitude and color-time diagrams. From low-flux spectra, we measured Mg II line and estimated the black hole mass.\\ Results: Ton 599 showed strong optical variability. Log-normal distributions fit the fluxes better, and all bands show a positive RMS-flux relation with red-noise PSDs.Intranight variability is detected, and used in constraining the emission region and magnetic field.The R band reaches a peak flux of 23.5 mJy, corresponding to a monochromatic luminosity of $log(νLν)= 48.48 [erg/s]$. We found a redder-when-brighter trend at low fluxes (thermal), achromatic behavior at intermediate levels (possibly due to jet orientation changes), and a bluer-when-brighter trend at high fluxes (synchrotron). Long-term color changes are modest, short-term are significant, with a negative correlation between the amplitude of color changes and the average flux. The estimated SMBH mass is order of $10^8 M_\odot$.

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

TL;DR

This study delivers a comprehensive, multi-year, multi-band optical variability analysis of the FSRQ Ton 599 using WEBT BVRI photometry (2011–2023) and Steward spectroscopy. By testing flux distributions, RMS–flux relations, and PSDs, it demonstrates log-normal long-term flux distributions with red-noise PSDs and detects intranight variability, constraining emission-region sizes and magnetic fields. The work further reveals intricate color evolution consistent with a two-component disk+jet model, and it estimates a central black hole mass of about from Mg II lines, situating Ton 599 among highly variable, jet-dominated AGN. The results provide robust constraints on jet emission, particle acceleration, and disk–jet coupling across timescales, and emphasize a complex, location-dependent picture of variability in this blazar.

Abstract

(Shortened)Context: We analyze the optical variability of the FSRQ Ton 599 using BVRI photometry from the WEBT collaboration (2011-2023), complemented by photometric and spectroscopic data from the Steward Observatory.\\ Aims: 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.\\ Methods: We tested flux distributions in each filter against normal and log-normal, explored the RMS-flux relation and derived PSDs. We quantified intranight variability using a 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, monochromatic luminosities and generated Color-magnitude and color-time diagrams. From low-flux spectra, we measured Mg II line and estimated the black hole mass.\\ Results: Ton 599 showed strong optical variability. Log-normal distributions fit the fluxes better, and all bands show a positive RMS-flux relation with red-noise PSDs.Intranight variability is detected, and used in constraining the emission region and magnetic field.The R band reaches a peak flux of 23.5 mJy, corresponding to a monochromatic luminosity of . We found a redder-when-brighter trend at low fluxes (thermal), achromatic behavior at intermediate levels (possibly due to jet orientation changes), and a bluer-when-brighter trend at high fluxes (synchrotron). Long-term color changes are modest, short-term are significant, with a negative correlation between the amplitude of color changes and the average flux. The estimated SMBH mass is order of .
Paper Structure (20 sections, 13 equations, 13 figures, 10 tables)

This paper contains 20 sections, 13 equations, 13 figures, 10 tables.

Table of Contents

  1. Introduction
  2. Optical data
  3. Analysis and results
  4. Global flux properties
  5. Flux distribution.
  6. RMS-flux relation.
  7. PSD distribution.
  8. Intranight and intraday flux variations
  9. Long-term variability
  10. Color analysis
  11. Estimation of the black hole mass
  12. Discussion
  13. Flux distribution and RMS-flux relation.
  14. Power spectral density.
  15. IDV analysis.
  16. ...and 5 more sections

Figures (13)

  • Figure 1: Flux density evolution of the blazar Ton 599 from November 2011 to September 2023 in B, V, R, and I filters. Colors and symbols in the plots are explained in Table \ref{['tab: observatories']}.
  • Figure 2: Left panel: Flux distribution from $\sim$12 years of R-band observations. The histogram (blue bars) shows the flux counts. The red curve is the best-fitting normal function, and the blue curve is the best-fitting log-normal function. Right panel: RMS (i.e., the square root of the excess variance) as a function of the mean flux, computed in (1) bins containing an equal number of data points (blue markers), and (2) bins of fixed time length (red markers). The solid blue and red lines indicate the best linear fits for each binning scheme.
  • Figure 3: R-band periodogram of Ton 599.
  • Figure 4: Intranight light curves displaying statistically significant variability based on the $\chi^2$ test. The vertical axis shows the measured magnitude, the legend indicates the filter used for each observation, and the horizontal axis represents the relative time in hours.
  • Figure 5: Zoomed-in R-band light curve from JD-2455000=3050 to 3300 (Period II) and from JD-2455000=4150 to 5120 (Period III) in the R band. Complex structure of the outbursts is visible. The inset highlights the second-largest peak, well sampled in all filters.
  • ...and 8 more figures