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Decade of blazar OJ 287 optical data: bluer-when-brighter holds, black hole at least 4 billion suns

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load-bearing objection Densely sampled OJ 287 optical light curve with a shaky BH mass estimate the 2 major comments →

arxiv 2607.07201 v1 pith:VAUZSKF4 submitted 2026-07-08 astro-ph.HE

Multi-band optical photometric variability of the blazar OJ 287 from 2015 to 2025

Alok C. Gupta , Karan Dogra , Mark Kidger , Mauri J. Valtonen , Paul J. Wiita , Pankaj Kushwaha , Sergey S. Savchenko , Sofia O. Kurtanidze
show 96 more authors
Svetlana G. Jorstad Alan P. Marscher Katsura Matsumoto Lang Cui Shao Ming Hu Goran Damljanovic Rumen Bachev O. Vince Mai Liao Zhongxiang Wang A. Darriba S. Haque F. S. Alfaro J. B. Amatller J. M. F. Andujar S. Arnold T. Arranz M. Bachini C. L. Barcelo S. Boeva G. A. Borman D. Boyd D. Buczinski J. D. Casal X. Chen J. M. Cores F. C. Cucarella P. U. Devanand V. Dhiman L. T. Espasa J. H. Fan R. G. Farfan J. R. Fernandez F. Garcia R. C. Garcia H. Gaur J. C. Gomez J. L. S. Gonzalez J. L. Gonzalez-Carballo T. S. Grishina F. H. Grondona M. F. Gu H. Guo V. A. Hagen-Thorn G. Hurst S. Ibryamov R. Z. Ivanidze N. James B. Jardine S. Johnstone M. D. Jovanovic N. Kalita S. Karge S. Kishore E. N. Kopatskaya O. M. Kurtanidze A. Kurtenkov E. G. Larionova E. R. Lorenz J. Lozano E. F. Mananes F. L. Martinez M. Mobberley M. Morales-Aimar D. A. Morozova M. G. Nikolashvili Y. Nikolov R. N. Nogues P. A. Novikova L. M. Penas A. E. Perez C. Perello R. Pickard F. G. Pinilla G. Poyner F. Rahmatullaeva B. Rajkumar N. G. Ribes E. Semkov E. V. Shishkina M. Stojanovic A. Strigachev T. Tripathi Yu. V. Troitskaya I. S. Troitskiy J. Valero A. A. Vasilyev B. Villarroel A. E. Volvach L. N. Volvach S. J. Wagner Z. R. Weaver Wen-Xin Yang Z. Zhang A. V. Zhovtan W. Zuo
This is my paper
classification astro-ph.HE PACS 98.54.Cm98.62.Js98.70.Ri
keywords OJ 287blazarBL Lacertae objectoptical variabilitybluer-when-brighterbinary black holeblack hole massdiscrete correlation function
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

This paper presents the most densely sampled multi-band optical light curve of the blazar OJ 287 to date, covering 2015 to 2025 with nearly 28,000 data points across B, V, R, and I filters. The central finding is that OJ 287 consistently follows a bluer-when-brighter trend: whenever the source brightens, its shorter-wavelength (blue) emission rises faster than its longer-wavelength (red) emission, and this pattern persists across all ten observing seasons and on both long and short timescales. Cross-correlating the four optical bands using a z-transformed discrete correlation function shows that variations in all bands peak at zero time lag, meaning the different colors are emitted from the same physical region in the jet. The authors also combine eight optical spectra taken during a low-flux state in late 2017, detect a weak [O III] emission line, and use its width as a proxy for stellar velocity dispersion in the M-sigma relation to estimate the central black hole mass at log(M_BH/M_sun) = 9.59 ± 0.40, or at least 3.89 billion solar masses. Because the jet points nearly at Earth and the emitting region is likely geometrically flattened, the observed line width is narrowed by projection effects, so the authors flag this as a lower limit consistent with the dynamically inferred mass of about 18 billion solar masses from the binary black hole model.

Core claim

The paper establishes that OJ 287's optical emission is co-spatial across B, V, R, and I bands (zero-lag cross-correlation) and follows a persistent bluer-when-brighter chromatic trend across a full decade of dense monitoring, while providing a spectroscopic lower bound on the central black hole mass of at least 3.89 × 10^9 solar masses from the [O III] line width.

What carries the argument

The bluer-when-brighter trend is the central diagnostic: it is quantified via linear fits to color-magnitude diagrams (B−R and V−R versus magnitude) across ten observing segments, yielding positive slopes and Spearman correlation coefficients up to 0.717. The co-spatiality claim rests on z-transformed discrete correlation functions between all band pairs peaking at zero lag with 3.5σ significance, assessed against 50,000 simulated light curves. The black hole mass estimate uses the FWHM of the [O III] λ5007 Å narrow emission line (841 km/s, corrected for instrumental broadening of 918 km/s) as a surrogate for stellar velocity dispersion in the Kormendy & Ho (2013) M-sigma relation, with the低

Load-bearing premise

The black hole mass estimate depends on using the width of the [O III] narrow emission line as a stand-in for stellar velocity dispersion in the M-sigma relation. Because the jet of OJ 287 points almost directly at Earth, the emitting gas is viewed nearly face-on, which artificially narrows the observed line width. The authors acknowledge this could underestimate the true mass by up to a factor of ten, so the quoted value is explicitly a lower limit rather than a precise mass

What would settle it

If future spectroscopic observations during low states detect broad Hα or Hβ lines and yield a virial mass estimate significantly below 3.89 × 10^9 solar masses (after inclination correction), or if the bluer-when-brighter trend reverses in a future flaring cycle, the core claims would be undermined.

Watch this falsifier — get emailed when new claim-graph text bears on it.

If this is right

  • If the bluer-when-brighter trend and zero-lag cross-correlation hold for future flaring cycles, it constrains emission-region models to single-zone synchrotron scenarios where harder-spectrum electrons dominate during bright states.
  • The spectroscopic mass lower limit of ~4 billion solar masses, combined with the acknowledged inclination correction of up to 10×, narrows the allowed parameter space for the binary black hole orbital model and its predicted gravitational wave signal.
  • The decade-long baseline with dense sampling provides a template for what temporal coverage is needed to distinguish periodic binary-impact flares from stochastic jet variability in other candidate binary SMBH systems.
  • Future spectroscopic monitoring during low states could detect Hα or Hβ broad lines, enabling a direct virial mass estimate that would bypass the [O III] surrogate and the large inclination uncertainty.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • If the bluer-when-brighter trend is driven by fresh electron injection with harder energy distributions, the degree of the color-magnitude slope could serve as a proxy for the hardness of the injected electron spectrum, testable against multi-wavelength spectral energy distribution modeling.
  • The zero-lag result across optical bands, combined with previously reported optical-gamma-ray lags of a few days, might imply a spatial offset between the synchrotron-emitting region and the inverse-Compton scattering region, which could be tested with simultaneous optical and gamma-ray monitoring during the next predicted flare.
  • The fact that the [O III] line is detected only in the averaged spectrum of eight low-state epochs suggests that jet continuum dilution in high states suppresses line visibility, meaning systematic spectroscopic monitoring during faint states is the most efficient strategy for virial mass work on BL Lac objects.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

2 major / 6 minor

Summary. This paper presents an extensive multi-band (BVRI) optical photometric monitoring campaign of the blazar OJ 287 spanning 2015–2025, comprising over 27,000 data points from a large network of ground-based observatories. The authors characterize variability amplitudes across 10 seasonal segments, demonstrate a persistent bluer-when-brighter (BWB) chromatic trend in both color–magnitude and color–time analyses, show zero-lag inter-band cross-correlations via the ZDCF method, and estimate a central black hole mass of log(M_BH/M☉) = 9.59 ± 0.40 using the [O III] λ5007 line width as a surrogate for stellar velocity dispersion in the M–σ relation. The dataset is among the most densely sampled optical light curves for any blazar and represents a valuable resource for the community.

Significance. The primary value of this work lies in the photometric dataset itself and its variability characterization. The BWB trend is quantified consistently across all ten segments with both Pearson and Spearman coefficients (Table 3), and the ZDCF analysis with simulated significance levels (3.5σ) is methodologically sound. The paper builds on the authors' prior monitoring efforts (Gupta et al. 2017, 2019, 2023) and provides a continuous record bridging the 2015 and 2019 predicted binary-SMBH impact flares. The dataset will be useful for multi-wavelength correlation studies and binary black hole model tests. The BH mass estimate, while carrying large systematic uncertainties, is presented as a lower limit and is consistent with the dynamically inferred mass from the binary model.

major comments (2)
  1. §4: The [O III] FWHM of 841 km/s is deconvolved from an instrumental resolution of ~918 km/s, meaning the measured line width is only ~1.35× the resolution—the line is marginally resolved at best. Moreover, the [O III] feature is detected only in the average of 8 spectra, not in any individual exposure. At this signal-to-noise and resolution ratio, the Gaussian FWHM fit is sensitive to continuum subtraction choices and to the assumed power-law index α. The 0.27 dex uncertainty from mock spectra captures statistical noise but not this systematic continuum-model dependence. Given that the M–σ relation exponent (β ≈ 4.38) amplifies FWHM errors by a factor of ~4.4 in log-mass, the authors should explicitly discuss how robust the deconvolved FWHM is to continuum model variations (e.g., varying α or using a different continuum window), and whether the quoted uncertainty adequately covers this.
  2. Abstract and §4: The phrase 'at least 3.89 × 10^9 M☉' is misleading. The value 3.89 × 10^9 (10^9.59) is the central estimate, not a statistical lower bound—the 1σ lower bound is ~1.5 × 10^9 (10^9.19). The 'at least' qualifier derives solely from the qualitative inclination argument (sin i correction), which is not quantified into the error budget. The abstract should either report the full estimate with its uncertainty (log M_BH = 9.59 ± 0.40) or, if the 'lower limit' framing is retained, clarify that it rests on the inclination argument rather than on the statistical error.
minor comments (6)
  1. §2: The inter-calibration between datasets from different telescopes is described qualitatively ('the great majority of the offsets were well within the measurement uncertainties'), but no quantitative summary of the offsets is provided. A table or sentence giving the typical offset magnitude and the number of data points affected would strengthen the analysis.
  2. §3.2, Figure 2: The color-magnitude diagrams would benefit from showing the typical photometric error bars, particularly for the B-band data where the number of simultaneous B–R pairs (1425) is smaller than V–R pairs (2110).
  3. §5 (Discussion): The discussion is largely a literature review and does not substantially advance physical interpretation beyond what is already known. For instance, the BWB trend is attributed to shock-accelerated electron cooling or injection of harder electron distributions, but no quantitative comparison to model predictions is attempted. While this is acceptable for an observational paper, the discussion could be tightened to focus on what the new data specifically reveal.
  4. Table 1: The 'Marker Color' column references colors used in Figure 1, but some entries (e.g., 'Lime', 'Crimson') may be difficult to distinguish in print. Consider using more distinct symbols or a legend inset.
  5. §4: The sentence 'The correction factor could be up to a factor of ten for the NLR' is stated without derivation or reference. A brief justification or citation would help the reader assess this claim.
  6. References: Several arXiv preprints are cited without journal publication information (e.g., P. Kushwaha 2025; S. M. Ressler et al. 2025). These should be updated if published versions are available.

Circularity Check

0 steps flagged

No circularity: observational results are directly measured from data, BH mass uses external M-sigma relation

full rationale

This is an observational astronomy paper, not a derivation chain. The three main results are each independently measured from data: (1) the bluer-when-brighter (BWB) trend is a direct empirical observation from color-magnitude diagrams with linear fits (Section 3.2, Table 3), not a quantity derived from a model that was itself fitted to the same data; (2) the zero-lag cross-correlation peaks (Section 3.3, Figure 4) are computed via ZDCF from the photometric time series, and the significance is assessed by simulating 5x10^4 light curves following Emmanoulopoulos et al. (2013) — an external method; (3) the BH mass estimate of log(M_BH/M_sun) = 9.59 ± 0.40 (Section 4) uses the [O III] FWHM as a surrogate for sigma in the M-sigma relation of Kormendy & Ho (2013), an externally published relation. The self-citations (Gupta et al. 2017, 2019, 2023) provide prior observational data points that are incorporated into the light curve, but the current paper's results are derived from new and combined data, not from re-packaging prior fitted parameters as predictions. The binary SMBH model is discussed as context (Section 5) but is not used to derive any of the paper's quantitative claims. The inclination correction argument (factor of ~10 for sin i) is a qualitative physical argument, not a circular definition. While the BH mass estimate has legitimate systematic concerns (the [O III] FWHM of 841 km/s is comparable to the instrumental resolution of 918 km/s, and the 'at least' framing conflates the central value with a lower limit), these are correctness/robustness issues, not circularity. No step in the paper reduces to its inputs by construction.

Axiom & Free-Parameter Ledger

2 free parameters · 4 axioms · 0 invented entities

The paper introduces no new physical entities or parameters beyond standard observational astronomy. The binary SMBH system is a pre-existing model from the literature (Sillanpaa et al. 1988; Valtonen et al.).

free parameters (2)
  • Power-law continuum index (alpha)
    Fitted to the average spectrum continuum as f_lambda proportional to lambda^alpha before [O III] line measurement (Section 4).
  • Cubic polynomial coefficients for color vs MJD = a=-0.059, b=0.040, c=0.106, d=0.809 (B-R); a=-0.044, b=0.040, c=0.074, d=0.367 (V-R)
    Fitted to color vs MJD trends in Figure 3 (Section 3.2).
axioms (4)
  • domain assumption The M-sigma relation of Kormendy & Ho (2013) applies to BL Lac objects.
    Section 4: used to convert [O III] FWHM (as sigma surrogate) to BH mass. The relation was derived for bulge-dominated galaxies, not jet-dominated BL Lacs.
  • domain assumption [O III] line width is a valid surrogate for stellar velocity dispersion sigma.
    Section 4: sigma = FWHM_[OIII]/2.35. This assumes the narrow-line region kinematics trace bulge gravity, which may not hold for all AGN.
  • domain assumption Inter-telescope photometric offsets are within measurement uncertainties.
    Section 2: 'The great majority of the offsets were well within the measurement uncertainties' — stated without tabulated offsets or quantitative analysis.
  • domain assumption The binary SMBH impact model predicts the observed flare periodicity.
    Section 1 and 5: the paper frames observations within the binary model framework, though noting spectral inconsistencies with thermal bremsstrahlung predictions.

pith-pipeline@v1.1.0-glm · 27373 in / 2464 out tokens · 496832 ms · 2026-07-09T17:21:37.927870+00:00 · methodology

0 comments
read the original abstract

We present the most densely sampled multi-band optical photometric observations of the peculiar BL Lacertae object OJ 287 from 2015 to 2025 with a focus on its optical activity on diverse timescales. We present a total of 2296, 10927, 11484, and 2982 data points in B, V, R, and I bands, respectively. The densely sampled observations allow us to keep track of the source evolution that it has exhibited since the start of the predicted major optical flaring activity at the end of 2015. The study reveals clear and persistent bluer when brighter trends in both the long-term and short-term variations. Different bands were cross-correlated with discrete correlation functions, which peak at zero lag, implying co-spatial emission. Using eight optical spectra in the low flux states of OJ 287 taken from 2017 October 21 to 2017 November 22, from Steward Observatory, we estimate the central black hole mass to be at least 3.89 $\times \ \rm{10}^{9} \ \rm{M}_{\odot}$ from the [O III] line width. The emission mechanism of the binary black hole blazar, and its possible implication in various aspects of multi-messenger astronomy are briefly discussed.

Figures

Figures reproduced from arXiv: 2607.07201 by A. A. Vasilyev, A. Darriba, A. E. Perez, A. E. Volvach, A. Kurtenkov, Alan P. Marscher, Alok C. Gupta, A. Strigachev, A. V. Zhovtan, B. Jardine, B. Rajkumar, B. Villarroel, C. L. Barcelo, C. Perello, D. A. Morozova, D. Boyd, D. Buczinski, E. F. Mananes, E. G. Larionova, E. N. Kopatskaya, E. R. Lorenz, E. Semkov, E. V. Shishkina, F. C. Cucarella, F. Garcia, F. G. Pinilla, F. H. Grondona, F. L. Martinez, F. Rahmatullaeva, F. S. Alfaro, G. A. Borman, G. Hurst, Goran Damljanovic, G. Poyner, H. Gaur, H. Guo, I. S. Troitskiy, J. B. Amatller, J. C. Gomez, J. D. Casal, J. H. Fan, J. L. Gonzalez-Carballo, J. Lozano, J. L. S. Gonzalez, J. M. Cores, J. M. F. Andujar, J. R. Fernandez, J. Valero, Karan Dogra, Katsura Matsumoto, Lang Cui, L. M. Penas, L. N. Volvach, L. T. Espasa, Mai Liao, Mark Kidger, Mauri J. Valtonen, M. Bachini, M. D. Jovanovic, M. F. Gu, M. G. Nikolashvili, M. Mobberley, M. Morales-Aimar, M. Stojanovic, N. G. Ribes, N. James, N. Kalita, O. M. Kurtanidze, O. Vince, Pankaj Kushwaha, P. A. Novikova, Paul J. Wiita, P. U. Devanand, R. C. Garcia, R. G. Farfan, R. N. Nogues, R. Pickard, Rumen Bachev, R. Z. Ivanidze, S. Arnold, S. Boeva, Sergey S. Savchenko, Shao Ming Hu, S. Haque, S. Ibryamov, S. Johnstone, S. J. Wagner, S. Karge, S. Kishore, Sofia O. Kurtanidze, Svetlana G. Jorstad, T. Arranz, T. S. Grishina, T. Tripathi, V. A. Hagen-Thorn, V. Dhiman, Wen-Xin Yang, W. Zuo, X. Chen, Y. Nikolov, Yu. V. Troitskaya, Zhongxiang Wang, Z. R. Weaver, Z. Zhang.

Figure 1
Figure 1. Figure 1: Multi-band optical light curve of OJ 287 from 2015 to 2025. The x-axis and y-axis represent modified Julian date (MJD) and optical magnitudes, respectively. All four light curves are divided into 10 segments due to seasonal gaps. The observatories providing the data are indicated by the shapes and colors of the points as defined in [PITH_FULL_IMAGE:figures/full_fig_p005_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: The left panels in the figure show the color-magnitude diagrams with a linear fit to all data points, whereas the right panels show the fit to all ten segments. 3.3. Z-transformed discrete correlation function To estimate the cross-correlation between these un￾evenly sampled time series, we employ the z-transformed discrete correlation function (ZDCF), originally intro￾duced by T. Alexander (1997). The ZDC… view at source ↗
Figure 3
Figure 3. Figure 3: Color vs MJD plots for OJ 287. The plots show a slowly varying component, fitted with a cubic polynomial (in black). aligned, with any lag mostly consistent with being zero or sometimes a few days (S. Vercellone et al. 2009; B. Rajput et al. 2019; G. Bhatta 2021). Such behav￾ior tends to favor leptonic models where synchrotron emission and inverse-Compton scattering (γ-rays) come from the same lepton popul… view at source ↗
Figure 4
Figure 4. Figure 4: Cross correlation results between different optical bands. With all ZDCFs peaking at zero lag, one can infer essentially co-spatial emission, with the red dashed line representing 3.5σ significance level. emission line is from the AGN narrow line emission region at the kpc scale, which is generally believed to be a cone structure rather than a disk; therefore, the projection effect may not be as important … view at source ↗
Figure 5
Figure 5. Figure 5: The eight spectra observed in the period of 2017.10.21-2017.11.22 and the flux average spectrum (left). All spectra were corrected for Galactic extinction and shifted to source rest-frame, with the position of emission lines of Hβ and [O III] λ5007˚A indicated as the vertical red dotted and green dotted lines; the spectral fitting of OJ 287 (right), where the continuum is fitted with a single power law sho… view at source ↗

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Works this paper leans on

103 extracted references · 103 canonical work pages · 5 internal anchors

  1. [1]

    A., Ackermann, M., Agudo, I., et al

    Abdo, A. A., Ackermann, M., Agudo, I., et al. 2010, ApJ, 716, 30, doi: 10.1088/0004-637X/716/1/30

    work page doi:10.1088/0004-637x/716/1/30 2010

  2. [2]

    M., et al

    Agazie, G., Anumarlapudi, A., Archibald, A. M., et al. 2023, ApJL, 951, L8, doi: 10.3847/2041-8213/acdac6

    work page doi:10.3847/2041-8213/acdac6 2023

  3. [3]

    1997, in Astrophysics and Space Science

    Alexander, T. 1997, in Astrophysics and Space Science

    work page 1997

  4. [4]

    218, Astronomical Time Series, ed

    Library, Vol. 218, Astronomical Time Series, ed. D. Maoz, A. Sternberg, & E. M. Leibowitz, 163, doi: 10.1007/978-94-015-8941-3 14 Ar´ evalo, P., & Uttley, P. 2006, MNRAS, 367, 801, doi: 10.1111/j.1365-2966.2006.09989.x

    work page doi:10.1007/978-94-015-8941-3 2006

  5. [5]

    A., & Hawley, J

    Balbus, S. A., & Hawley, J. F. 1991, ApJ, 376, 214, doi: 10.1086/170270

    work page doi:10.1086/170270 1991

  6. [6]

    2021, ApJ, 923, 7, doi: 10.3847/1538-4357/ac2819

    Bhatta, G. 2021, ApJ, 923, 7, doi: 10.3847/1538-4357/ac2819

    work page doi:10.3847/1538-4357/ac2819 2021

  7. [7]

    2016, ApJ, 832, 47, doi: 10.3847/0004-637X/832/1/47

    Bhatta, G., Zola, S., Stawarz, L., et al. 2016, ApJ, 832, 47, doi: 10.3847/0004-637X/832/1/47

    work page doi:10.3847/0004-637x/832/1/47 2016

  8. [8]

    2024, in SF2A-2024: Proceedings of the Annual meeting of the French Society of Astronomy and Astrophysics, ed

    Bonnassieux, E., Shetgaonkar, H., & Kadler, M. 2024, in SF2A-2024: Proceedings of the Annual meeting of the French Society of Astronomy and Astrophysics, ed. M. B´ ethermin, K. Bailli´ e, N. Lagarde, J. Malzac, R. M

    work page 2024

  9. [9]

    M., Bailyn, C., et al

    Bonning, E., Urry, C. M., Bailyn, C., et al. 2012, ApJ, 756, 13, doi: 10.1088/0004-637X/756/1/13

    work page doi:10.1088/0004-637x/756/1/13 2012

  10. [10]

    W., Bailyn, C., Urry, C

    Bonning, E. W., Bailyn, C., Urry, C. M., et al. 2009, ApJL, 697, L81, doi: 10.1088/0004-637X/697/2/L81

    work page doi:10.1088/0004-637x/697/2/l81 2009

  11. [11]

    O., & VERITAS Collaboration

    Brien, S. O., & VERITAS Collaboration. 2017, in International Cosmic Ray Conference, Vol. 301, 35th International Cosmic Ray Conference (ICRC2017), 650

    work page 2017

  12. [12]

    2023, ApJ, 951, 106, doi: 10.3847/1538-4357/accbbc

    Britzen, S., Zajaˇ cek, M., Gopal-Krishna, et al. 2023, ApJ, 951, 106, doi: 10.3847/1538-4357/accbbc

    work page doi:10.3847/1538-4357/accbbc 2023

  13. [13]

    2018, MNRAS, 478, 3199, doi: 10.1093/mnras/sty1026

    Britzen, S., Fendt, C., Witzel, G., et al. 2018, MNRAS, 478, 3199, doi: 10.1093/mnras/sty1026

    work page doi:10.1093/mnras/sty1026 2018

  14. [14]

    S., & Pushkarev, A

    Butuzova, M. S., & Pushkarev, A. B. 2020, Universe, 6, 191, doi: 10.3390/universe6110191

    work page doi:10.3390/universe6110191 2020

  15. [15]

    H., & Lee, C

    Chan, M. H., & Lee, C. M. 2024, ApJL, 962, L40, doi: 10.3847/2041-8213/ad2465

    work page doi:10.3847/2041-8213/ad2465 2024

  16. [16]

    2018, MNRAS, 481, 2249, doi: 10.1093/mnras/sty2268

    Chen, J.-W., & Zhang, Y. 2018, MNRAS, 481, 2249, doi: 10.1093/mnras/sty2268

    work page doi:10.1093/mnras/sty2268 2018

  17. [17]

    , keywords =

    Chen, X., Fossati, G., Liang, E. P., & B¨ ottcher, M. 2011, MNRAS, 416, 2368, doi: 10.1111/j.1365-2966.2011.19215.x

    work page doi:10.1111/j.1365-2966.2011.19215.x 2011

  18. [18]

    L., Lico, R., et al

    Cho, I., G´ omez, J. L., Lico, R., et al. 2024, A&A, 683, A248, doi: 10.1051/0004-6361/202347157

    work page doi:10.1051/0004-6361/202347157 2024

  19. [19]

    H., Aller, H

    Cohen, M. H., Aller, H. D., Aller, M. F., et al. 2018, ApJ, 862, 1, doi: 10.3847/1538-4357/aacb31 de Naurois, M. 2021, Universe, 7, 421, doi: 10.3390/universe7110421 2015-2025 Optical Variability of OJ 28715

    work page doi:10.3847/1538-4357/aacb31 2018

  20. [20]

    Deb, D., Gopakumar, A., & Valtonen, M. J. 2025, ApJL, 984, L66, doi: 10.3847/2041-8213/adcee3 Di Gesu, L., Marshall, H. L., Ehlert, S. R., et al. 2023, Nature Astronomy, 7, 1245, doi: 10.1038/s41550-023-02032-7

    work page doi:10.3847/2041-8213/adcee3 2025

  21. [21]

    C., Raiteri, C

    Dogra, K., Gupta, A. C., Raiteri, C. M., et al. 2025, ApJS, 276, 1, doi: 10.3847/1538-4365/ad8e3d

    work page doi:10.3847/1538-4365/ad8e3d 2025

  22. [22]

    A., & Krolik, J

    Edelson, R. A., & Krolik, J. H. 1988, ApJ, 333, 646, doi: 10.1086/166773

    work page doi:10.1086/166773 1988

  23. [23]

    M., & Papadakis, I

    Emmanoulopoulos, D., McHardy, I. M., & Papadakis, I. E. 2013, MNRAS, 433, 907, doi: 10.1093/mnras/stt764

    work page doi:10.1093/mnras/stt764 2013

  24. [24]

    doi:10.1046/j.1365-8711.1998.01589.x , keywords =

    Ghisellini, G. 1998, MNRAS, 299, 433, doi: 10.1046/j.1365-8711.1998.01828.x

    work page doi:10.1046/j.1365-8711.1998.01828.x 1998

  25. [25]

    2019, Nature Astronomy, 3, 88, doi: 10.1038/s41550-018-0610-1

    Gao, S., Fedynitch, A., Winter, W., & Pohl, M. 2019, Nature Astronomy, 3, 88, doi: 10.1038/s41550-018-0610-1

    work page doi:10.1038/s41550-018-0610-1 2019

  26. [26]

    doi:10.1046/j.1365-8711.1998.01589.x , keywords =

    Comastri, A. 1998, MNRAS, 301, 451, doi: 10.1046/j.1365-8711.1998.02032.x

    work page doi:10.1046/j.1365-8711.1998.02032.x 1998

  27. [27]

    2018, MNRAS, 475, L15, doi: 10.1093/mnrasl/slx203 Gonz´ alez-P´ erez, J

    Giesers, B., Dreizler, S., Husser, T.-O., et al. 2018, MNRAS, 475, L15, doi: 10.1093/mnrasl/slx203 Gonz´ alez-P´ erez, J. N., Kidger, M. R., & Mart´ ın-Luis, F. 2001, AJ, 122, 2055, doi: 10.1086/322129 Gopal-Krishna. 2024, A&A, 688, L16, doi: 10.1051/0004-6361/202449409

    work page doi:10.1093/mnrasl/slx203 2018

  28. [28]

    2018, ApJ, 863, 175, doi: 10.3847/1538-4357/aad2de

    Goyal, A., Stawarz, L., Zola, S., et al. 2018, ApJ, 863, 175, doi: 10.3847/1538-4357/aad2de

    work page doi:10.3847/1538-4357/aad2de 2018

  29. [29]

    F., & Ai, Y

    Gu, M. F., & Ai, Y. L. 2011, A&A, 528, A95, doi: 10.1051/0004-6361/201016280

    work page doi:10.1051/0004-6361/201016280 2011

  30. [30]

    F., Lee, C

    Gu, M. F., Lee, C. U., Pak, S., Yim, H. S., & Fletcher, A. B. 2006, A&A, 450, 39, doi: 10.1051/0004-6361:20054271

    work page doi:10.1051/0004-6361:20054271 2006

  31. [31]

    C., Agarwal, A., Mishra, A., et al

    Gupta, A. C., Agarwal, A., Mishra, A., et al. 2017, MNRAS, 465, 4423, doi: 10.1093/mnras/stw3045

    work page doi:10.1093/mnras/stw3045 2017

  32. [32]

    C., Gaur, H., Wiita, P

    Gupta, A. C., Gaur, H., Wiita, P. J., et al. 2019, AJ, 157, 95, doi: 10.3847/1538-3881/aafe7d

    work page doi:10.3847/1538-3881/aafe7d 2019

  33. [33]

    C., Kushwaha, P., Carrasco, L., et al

    Gupta, A. C., Kushwaha, P., Carrasco, L., et al. 2022, ApJS, 260, 39, doi: 10.3847/1538-4365/ac6c2c

    work page doi:10.3847/1538-4365/ac6c2c 2022

  34. [34]

    C., Kushwaha, P., Valtonen, M

    Gupta, A. C., Kushwaha, P., Valtonen, M. J., et al. 2023, ApJL, 957, L11, doi: 10.3847/2041-8213/acfd2e

    work page doi:10.3847/2041-8213/acfd2e 2023

  35. [35]

    2025, MNRAS, 540, 582, doi: 10.1093/mnras/staf713

    Harutyunyan, G., Sahakyan, N., & B´ egu´ e, D. 2025, MNRAS, 540, 582, doi: 10.1093/mnras/staf713

    work page doi:10.1093/mnras/staf713 2025

  36. [36]

    2021, ApJ, 920, 12, doi: 10.3847/1538-4357/ac0eff

    Huang, S., Hu, S., Yin, H., et al. 2021, ApJ, 920, 12, doi: 10.3847/1538-4357/ac0eff

    work page doi:10.3847/1538-4357/ac0eff 2021

  37. [37]

    2023, PASJ, 75, 1, doi: 10.1093/pasj/psac084

    Imazawa, R., Sasada, M., Hazama, N., et al. 2023, PASJ, 75, 1, doi: 10.1093/pasj/psac084

    work page doi:10.1093/pasj/psac084 2023

  38. [38]

    2001, PASJ, 53, 79, doi: 10.1093/pasj/53.1.79

    Isobe, N., Tashiro, M., Sugiho, M., & Makishima, K. 2001, PASJ, 53, 79, doi: 10.1093/pasj/53.1.79

    work page doi:10.1093/pasj/53.1.79 2001

  39. [39]

    2022, pyZDCF: Initial Release, v1.0.0 Zenodo, doi: 10.5281/zenodo.7253034

    Nikutta, R. 2022, pyZDCF: Initial Release, v1.0.0 Zenodo, doi: 10.5281/zenodo.7253034

    work page doi:10.5281/zenodo.7253034 2022

  40. [40]

    2018, MNRAS, 480, 407, doi: 10.1093/mnras/sty1803

    Kapanadze, B., Vercellone, S., Romano, P., et al. 2018, MNRAS, 480, 407, doi: 10.1093/mnras/sty1803

    work page doi:10.1093/mnras/sty1803 2018

  41. [41]

    C., & Wiita, P

    Kishore, S., Gupta, A. C., & Wiita, P. J. 2024, ApJ, 960, 11, doi: 10.3847/1538-4357/ad0b80

    work page doi:10.3847/1538-4357/ad0b80 2024

  42. [42]

    C., et al

    Komossa, S., Grupe, D., Gallo, L. C., et al. 2021a, ApJ, 923, 51, doi: 10.3847/1538-4357/ac1442

    work page doi:10.3847/1538-4357/ac1442

  43. [43]

    L., et al

    Komossa, S., Grupe, D., Parker, M. L., et al. 2020, MNRAS, 498, L35, doi: 10.1093/mnrasl/slaa125

    work page doi:10.1093/mnrasl/slaa125 2020

  44. [44]

    2007, ApJL, 667, L33, doi: 10.1086/522002

    Komossa, S., & Xu, D. 2007, ApJL, 667, L33, doi: 10.1086/522002

    work page doi:10.1086/522002 2007

  45. [45]

    2017, in New Frontiers in Black Hole Astrophysics, ed

    Komossa, S., Grupe, D., Schartel, N., et al. 2017, in New Frontiers in Black Hole Astrophysics, ed. A. Gomboc, Vol. 324, 168–171, doi: 10.1017/S1743921317001648

    work page doi:10.1017/s1743921317001648 2017

  46. [46]

    L., et al

    Komossa, S., Grupe, D., Parker, M. L., et al. 2021b, MNRAS, 504, 5575, doi: 10.1093/mnras/stab1223

    work page doi:10.1093/mnras/stab1223

  47. [47]

    2021c, Universe, 7, 261, doi: 10.3390/universe7080261

    Komossa, S., Grupe, D., Kraus, A., et al. 2021c, Universe, 7, 261, doi: 10.3390/universe7080261

    work page doi:10.3390/universe7080261

  48. [48]

    2023a, ApJ, 944, 177, doi: 10.3847/1538-4357/acaf71

    Komossa, S., Kraus, A., Grupe, D., et al. 2023a, ApJ, 944, 177, doi: 10.3847/1538-4357/acaf71

    work page doi:10.3847/1538-4357/acaf71

  49. [49]

    2023b, MNRAS, 522, L84, doi: 10.1093/mnrasl/slad016

    Komossa, S., Grupe, D., Kraus, A., et al. 2023b, MNRAS, 522, L84, doi: 10.1093/mnrasl/slad016

    work page doi:10.1093/mnrasl/slad016

  50. [50]

    Kormendy, J., & Ho, L. C. 2013, ARA&A, 51, 511, doi: 10.1146/annurev-astro-082708-101811

    work page internal anchor Pith review doi:10.1146/annurev-astro-082708-101811 2013

  51. [51]

    2020, Galaxies, 8, 15, doi: 10.3390/galaxies8010015

    Kushwaha, P. 2020, Galaxies, 8, 15, doi: 10.3390/galaxies8010015

    work page doi:10.3390/galaxies8010015 2020

  52. [52]

    2022, Journal of Astrophysics and Astronomy, 43, 79, doi: 10.1007/s12036-022-09872-1

    Kushwaha, P. 2022, Journal of Astrophysics and Astronomy, 43, 79, doi: 10.1007/s12036-022-09872-1

    work page doi:10.1007/s12036-022-09872-1 2022

  53. [53]

    2025, Universe, 11, 84, doi: 10.3390/universe11030084

    Kushwaha, P. 2025, Universe, 11, 84, doi: 10.3390/universe11030084

    work page doi:10.3390/universe11030084 2025

  54. [54]

    2021, ApJ, 921, 18, doi: 10.3847/1538-4357/ac19b8

    Kushwaha, P., Pal, M., Kalita, N., et al. 2021, ApJ, 921, 18, doi: 10.3847/1538-4357/ac19b8

    work page doi:10.3847/1538-4357/ac19b8 2021

  55. [55]

    Kushwaha, P., Sahayanathan, S., & Singh, K. P. 2013, MNRAS, 433, 2380, doi: 10.1093/mnras/stt904

    work page doi:10.1093/mnras/stt904 2013

  56. [56]

    C., Wiita, P

    Kushwaha, P., Gupta, A. C., Wiita, P. J., et al. 2018a, MNRAS, 479, 1672, doi: 10.1093/mnras/sty1499

    work page doi:10.1093/mnras/sty1499

  57. [57]

    C., Wiita, P

    Kushwaha, P., Gupta, A. C., Wiita, P. J., et al. 2018b, MNRAS, 473, 1145, doi: 10.1093/mnras/stx2394

    work page doi:10.1093/mnras/stx2394

  58. [58]

    2020, ApJL, 894, L1, doi: 10.3847/2041-8213/ab79a4

    Laine, S., Dey, L., Valtonen, M., et al. 2020, ApJL, 894, L1, doi: 10.3847/2041-8213/ab79a4

    work page doi:10.3847/2041-8213/ab79a4 2020

  59. [59]

    J., & Valtonen, M

    Lehto, H. J., & Valtonen, M. J. 1996, ApJ, 460, 207, doi: 10.1086/176962

    work page doi:10.1086/176962 1996

  60. [60]

    2020, MNRAS, 491, 92, doi: 10.1093/mnras/stz2981

    Liao, M., & Gu, M. 2020, MNRAS, 491, 92, doi: 10.1093/mnras/stz2981

    work page doi:10.1093/mnras/stz2981 2020

  61. [61]

    H., Bai, J

    Liao, N. H., Bai, J. M., Liu, H. T., et al. 2014, ApJ, 783, 83, doi: 10.1088/0004-637X/783/2/83

    work page doi:10.1088/0004-637x/783/2/83 2014

  62. [62]

    Lyubarskii, Y. E. 1997, MNRAS, 292, 679, doi: 10.1093/mnras/292.3.679 16Gupta et al. MAGIC Collaboration, Abe, H., Abe, S., et al. 2024, A&A, 682, A114, doi: 10.1051/0004-6361/202347845

    work page doi:10.1093/mnras/292.3.679 1997

  63. [63]

    2019, MNRAS, 490, 124, doi: 10.1093/mnras/stz2557

    Majumder, A., Mitra, K., Chatterjee, R., et al. 2019, MNRAS, 490, 124, doi: 10.1093/mnras/stz2557

    work page doi:10.1093/mnras/stz2557 2019

  64. [64]

    Marscher, A. P. 2014, ApJ, 780, 87, doi: 10.1088/0004-637X/780/1/87

    work page doi:10.1088/0004-637x/780/1/87 2014

  65. [65]

    P., & Gear, W

    Marscher, A. P., & Gear, W. K. 1985, ApJ, 298, 114, doi: 10.1086/163592

    work page doi:10.1086/163592 1985

  66. [66]

    Mastichiadis, A., & Kirk, J. G. 2002, PASA, 19, 138, doi: 10.1071/AS01108

    work page doi:10.1071/as01108 2002

  67. [67]

    K., Bhatta, G., & Kizhakkekalam, S

    Navaneeth, P. K., Bhatta, G., & Kizhakkekalam, S. 2025, MNRAS, 544, 2455, doi: 10.1093/mnras/staf1781

    work page doi:10.1093/mnras/staf1781 2025

  68. [68]

    O., Lehto, H

    Nilsson, K., Takalo, L. O., Lehto, H. J., & Sillanp¨ a¨ a, A. 2010, A&A, 516, A60, doi: 10.1051/0004-6361/201014198

    work page doi:10.1051/0004-6361/201014198 2010

  69. [69]

    C., & Pawar, P

    Pal, M., Kushwaha, P., Dewangan, G. C., & Pawar, P. K. 2020, ApJ, 890, 47, doi: 10.3847/1538-4357/ab65ee

    work page doi:10.3847/1538-4357/ab65ee 2020

  70. [70]

    2022, Galaxies, 10, 35, doi: 10.3390/galaxies10010035

    Prandini, E., & Ghisellini, G. 2022, Galaxies, 10, 35, doi: 10.3390/galaxies10010035

    work page doi:10.3390/galaxies10010035 2022

  71. [71]

    2021, A&A, 654, A38, doi: 10.1051/0004-6361/202140708

    Prince, R., Agarwal, A., Gupta, N., et al. 2021, A&A, 654, A38, doi: 10.1051/0004-6361/202140708

    work page doi:10.1051/0004-6361/202140708 2021

  72. [72]

    M., Villata, M., Larionov, V

    Raiteri, C. M., Villata, M., Larionov, V. M., et al. 2008, A&A, 491, 755, doi: 10.1051/0004-6361:200810869

    work page doi:10.1051/0004-6361:200810869 2008

  73. [73]

    M., Nicastro, F., Stamerra, A., et al

    Raiteri, C. M., Nicastro, F., Stamerra, A., et al. 2017a, MNRAS, 466, 3762, doi: 10.1093/mnras/stw3333

    work page doi:10.1093/mnras/stw3333

  74. [74]

    M., Villata, M., Acosta-Pulido, J

    Raiteri, C. M., Villata, M., Acosta-Pulido, J. A., et al. 2017b, Nature, 552, 374, doi: 10.1038/nature24623

    work page doi:10.1038/nature24623

  75. [75]

    M., Villata, M., Jorstad, S

    Raiteri, C. M., Villata, M., Jorstad, S. G., et al. 2023, MNRAS, 522, 102, doi: 10.1093/mnras/stad942

    work page doi:10.1093/mnras/stad942 2023

  76. [76]

    Mandal, A. K. 2019, MNRAS, 486, 1781, doi: 10.1093/mnras/stz941

    work page doi:10.1093/mnras/stz941 2019

  77. [77]

    M., Combi, L., Ripperda, B., & Li, X

    Ressler, S. M., Combi, L., Ripperda, B., & Li, X. 2025, ApJL, 993, L22, doi: 10.3847/2041-8213/ae11ab Rodr´ ıguez-Ram´ ırez, J. C., Kushwaha, P., de Gouveia Dal

    work page doi:10.3847/2041-8213/ae11ab 2025

  78. [78]

    M., & Santos-Lima, R

    Pino, E. M., & Santos-Lima, R. 2020, MNRAS, 498, 5424, doi: 10.1093/mnras/staa2664

    work page doi:10.1093/mnras/staa2664 2020

  79. [79]

    R., Gupta, A

    Sarkar, A., Chitnis, V. R., Gupta, A. C., et al. 2019, ApJ, 887, 185, doi: 10.3847/1538-4357/ab5281

    work page doi:10.3847/1538-4357/ab5281 2019

  80. [80]

    J., Finkbeiner, D

    Schlegel, D. J., Finkbeiner, D. P., & Davis, M. 1998, ApJ, 500, 525, doi: 10.1086/305772

    work page internal anchor Pith review doi:10.1086/305772 1998

Showing first 80 references.