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Multi-wavelength picture of the misaligned BL Lac object 3C 371

T0 review · 2 major / 10 minor · reviewed 2026-08-11 · deepseek-v4-flash

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Pith's one-line read Using 18 very long baseline interferometry images, the paper tracks a superluminal knot in the jet of 3C 371 and derives a viewing angle of about 10 degrees, a Doppler factor around 6, and a bulk Lorentz factor around 6.

desk verdict First superluminal-motion detection for 3C 371, well analysed; the Doppler-factor estimate has an untested decay-shape assumption that the referee should probe. read the letter →

arxiv 2412.04068 v2 pith:UGNVNRBR submitted 2024-12-05 astro-ph.HE astro-ph.GA

J. Otero-Santos , C. M. Raiteri , A. Tramacere , J. Escudero Pedrosa , J. A. Acosta-Pulido , M. I. Carnerero , M. Villata , I. Agudo
show 47 more authors
I. A. Rahimov T. S. Andreeva D. V. Ivanov N. Marchili S. Righini M. Giroletti M. A. Gurwell S. S. Savchenko D. Carosati W. P. Chen S. O. Kurtanidze M. D. Joner E. Semkov T. Pursimo E. Benítez G. Damljanovic G. Andreuzzi G. Apolonio G. A. Borman V. Bozhilov F. J. Galindo-Guil T. S. Grishina V. A. Hagen-Thorn D. Hiriart H. Y. Hsiao S. Ibryamov R. Z. Ivanidze G. N. Kimeridze E. N. Kopatskaya O. M. Kurtanidze V. M. Larionov E. G. Larionova L. V. Larionova M. Minev D. A. Morozova M. G. Nikolashvili E. Ovcharov L. A. Sigua M. Stojanovic I. S. Troitskiy Yu. V. Troitskaya A. Tsai A. Valcheva A. A. Vasilyev O. Vince E. Zaharieva A. V. Zhovtan
This is my paper · ORCID
classification astro-ph.HEastro-ph.GA
keywords BLLacertaeobjects3C371activegalacticnucleirelativisticjetssuperluminalmotionmultiwavelengthvariabilityspectralenergydistributionVLBIimaging
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

This paper tries to establish that the BL Lac object 3C 371, long suspected of being seen at an unusually large angle for a blazar, really does have its jet tilted about ten degrees away from our line of sight. The evidence comes from 18 radio images taken over eighteen months that track one bright jet knot moving at an apparent speed of about 5.9 times the speed of light. Combining this motion with the knot's exponential brightness decay, the authors derive a Doppler factor of about 6, a bulk Lorentz factor of about 6, and a viewing angle of about 9.6 degrees. If correct, this resolves the source's debated classification by showing it is a BL Lac object whose jet is misaligned enough that the radio lobes are visible, and it anchors the interpretation of the source's radio-to-gamma-ray variability as synchrotron plus synchrotron-self-Compton emission.

What carries the argument

The load-bearing object is component B4, a bright compact knot in the 15 GHz VLBI images whose centroid advances almost linearly along the jet and whose flux density decays as $F = F_0 e^{-t/t_{\rm var}}$. The identity that carries the argument is the standard relativistic-jet relation linking the fitted apparent speed $\beta_{\rm app} = 5.9 \pm 0.8$, the e-folding variability timescale $t_{\rm var}$, and the resulting Doppler factor $\delta = 6.0 \pm 1.1$, from which the Lorentz factor $\Gamma = 6.0 \pm 1.8$ and viewing angle $\theta = (9.6 \pm 1.6)^\circ$ follow through the formalism of Jorstad et al. (2005). This same kinematic set later constrains the one-zone leptonic SED model, making the radio knot the anchor for the broad-band interpretation.

What would settle it

Re-fit component B4's flux decline with power-law or Gaussian flare profiles and recompute $t_{\rm var}$; if $t_{\rm var}$ changes by more than a factor of about two, the quoted $\delta = 6.0$, $\Gamma = 6.0$, and $\theta = 9.6^\circ$ would shift beyond their $1\sigma$ errors. A direct independent check would be a brightness-temperature Doppler factor measured from the same VLBI images, or a gamma-ray flare variability timescale that contradicts $\delta \approx 6$.

Watch

Extended reading notes

Core claim

The central discovery is that component B4 of the parsec-scale jet moves superluminally and its flux decays exponentially, allowing the standard variability-Doppler formalism to be applied. The authors report an apparent speed of $\beta_{\rm app} = 5.9 \pm 0.8$ in units of the speed of light, a Doppler factor of $\delta = 6.0 \pm 1.1$, a bulk Lorentz factor of $\Gamma = 6.0 \pm 1.8$, and a viewing angle of $\theta = (9.6 \pm 1.6)^\circ$. These numbers place 3C 371 as a moderately relativistic jet viewed off-axis, which explains why the optical, UV, X-ray, and gamma-ray emissions vary together while the radio emission anti-correlates and lags, and why a one-zone leptonic model with a hard electron distribution and negligible external Compton reproduces the high and low emission states.

Load-bearing premise

The derived Doppler factor, Lorentz factor, and viewing angle all rest on treating component B4's radio flux decay as a single exponential $F = F_0 e^{-t/t_{\rm var}}$; if the flux decline follows a different flare profile, the variability timescale and everything built on it shifts, even though the apparent speed itself would survive.

Editorial extensions

If this is right

  • The source's jet is not pointing at us: with $\theta \approx 10^\circ$, 3C 371 occupies a middle ground between blazars and radio galaxies, matching the two visible radio lobes reported in earlier work.
  • The high observed variability amplitudes in gamma-rays and optical are consistent with changes in the particle distribution and Doppler factor rather than a fully aligned jet, and the radio/optical anti-correlation points to different emission zones along the jet.
  • The one-zone leptonic model with synchrotron self-Compton, a faint accretion disc, and negligible external Compton reproduces both high and low states, with the high state explained mainly by a harder electron distribution ($p \approx 1.85$ versus $2.46$) and slightly larger magnetic field and Lorentz factor.
  • The radio polarization degree anti-correlates with total radio flux, and the radio electric-vector position angle settles near $80^\circ$, aligning with the optical EVPA after the optical slow rotation, indicating a common magnetic-field ordering at both wavelengths.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • If the viewing angle really is about $10^\circ$, then the long-term optical variability could be driven by modest Doppler-factor changes, and the source's gamma-ray emission should be intrinsically weaker than if the jet were aligned, predicting that future gamma-ray observations will continue to show a relatively steep and faint spectrum.
  • The same exponential-decay formalism failed for the slower or fainter jet components B1-B3 and B5-L0; if deeper VLBI imaging recovers their motions, the derived $\theta$, $\delta$, and $\Gamma$ for B4 could be cross-checked independently.
  • A promising test of the misalignment picture would be to watch whether the B4 trajectory curves in later VLBI epochs: a curved path would support helical-jet models and could revise the single viewing-angle estimate.
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Editorial analysis

A structured set of objections, weighed in public.

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

Referee Report

2 major / 10 minor

Summary. The paper presents a multiwavelength study of the BL Lac object 3C 371 using WEBT optical and radio monitoring, Swift-UVOT/XRT, Fermi-LAT, and MOJAVE 15 GHz VLBI data covering 2018-2020. The authors quantify long-term variability with the amplitude parameter, interband correlations via the ZDCF with Monte Carlo significance estimates, spectral variability in the optical, X-ray, and gamma-ray bands, and radio/optical polarization behavior. A kinematic analysis of 18 VLBI epochs identifies component B4 with superluminal apparent motion beta_app = 5.9 +/- 0.8, from which the viewing angle theta = (9.6 +/- 1.6) deg, Doppler factor delta = 6.0 +/- 1.1, and Lorentz factor Gamma = 6.0 +/- 1.8 are derived assuming an exponential decay timescale. Two broadband SEDs (high and low states) are fitted with a one-zone leptonic model including SSC and EC components, and the difference between states is attributed mainly to a hardening of the electron distribution (p = 1.85 versus 2.46). The overall conclusion is that 3C 371 is a misaligned BL Lac object whose jet is viewed at about 10 degrees.

Significance. If the kinematic parameters are robust, the paper delivers the first superluminal detection for 3C 371 and places it in the context of misaligned BL Lacs, which is a genuinely useful result for jet-population studies. The strengths of the manuscript include the large coordinated dataset, the careful correlation analysis based on 10^4 simulated light curves with matched PSD and PDF, the MCMC-based uncertainty evaluation of the SED fits in Appendix C, the explicit handling of host-galaxy subtraction and UVOT recalibration, and the public release of the modelfit tables on Zenodo. The authors are also appropriately cautious in several places, explicitly caveating the sampling-limited radio anti-correlation, the non-simultaneity of some SED data, and the degeneracy of the one-zone models. The main risk is concentrated in the kinematic parameter estimation: the values of delta, Gamma, and theta all inherit the assumed exponential decay form for the flux of component B4, so the stress-test concern about this assumption does land and needs to be addressed before the headline numbers can be taken at face value.

major comments (2)
  1. [Section 4, Figs. 9-10] The quoted kinematic parameters delta = 6.0 +/- 1.1, Gamma = 6.0 +/- 1.8, and theta = (9.6 +/- 1.6) deg all depend on the variability timescale t_var obtained from fitting component B4's flux to a single exponential decay F = F0 e^{-t/t_var}, following Weaver et al. (2022). The paper states that among the nine identified components only B4 was adequately fitted by this form; no alternative decay profiles (e.g., linear, power-law, or one-sided flare) are tested, so the exponential is assumed a priori rather than validated. Because the Jorstad et al. (2005) formula propagates t_var directly into delta, with Gamma and theta then derived from beta_app and delta, a different but equally plausible decay shape would shift all three parameters beyond the quoted statistical errors, which do not include the decay-model systematic. With beta_app about 5.9 and delta about 6.0, the solution sits near the geometric limit, so this matters quantitatively. I request a robustness analysis (for instance, fitting linear or power-law decays, estimating t_var from the 15 GHz total-flux light curve, or adopting a conservative systematic term) and a discussion of how delta, Gamma, and theta change under those alternatives; the superluminal result beta_app = 5.9 +/- 0.8 will stand regardless, but the derived angles and Doppler factor are the headline numbers.
  2. [Section 7, Table 7, and Section 8] The abstract and Section 8 state that the difference between the high and low emission states can be ascribed mainly to a hardening of the distribution of particles; as presented, this is a restatement of the fitted index p (1.85 versus 2.46) rather than an independent inference, since p is a free parameter of the JetSeT fit. The degeneracy warning in Appendix C is welcome, but it does not establish that the p difference is robust: the same SEDs could plausibly be reproduced by compensating changes in B, N, gamma_cut, or in the partly constrained values of Gamma and theta, and the MCMC corner plots in Figs. C.2-C.3 do not by themselves show that the high- and low-state p distributions are separated at a significant level. The authors should either demonstrate the robustness of the p difference (e.g., with a joint fit or a parameter scan showing it cannot be absorbed by other parameters) or explicitly soften the claim to one of a model-consistent interpretation, as they already do in Appendix C.
minor comments (10)
  1. [Section 2.5] The final paragraph contains a duplicated word: 'further in in Sect. 3' should read 'further in Sect. 3'.
  2. [Section 2.6 / Appendix B] The text and Appendix A state that 18 VLBI epochs spanning 2019 Aug 15 to 2021 Feb 5 were analysed, but Table B.1 lists 21 observation dates, including 2021 Feb 21, Mar 21, and Apr 9; the discrepancy should be clarified.
  3. [Section 5.3] The reported chi-squared per degree of freedom of 0.01 for the fit of the X-ray photon-index light curve to a constant is implausibly low and suggests either a typo or overestimated uncertainties; please verify the value and the statement that this supports no significant variation.
  4. [Section 5.4 and Table 6] The high-state gamma-ray photon index (2.42 +/- 0.12) is numerically steeper than the low-state value (2.14 +/- 0.18), which at face value runs opposite to the claimed hardening of the electron distribution in the high state; although the difference is not formally significant, a sentence explaining why this is compatible with the model would avoid confusion.
  5. [Section 7, Table 7] The SED-derived theta and Gamma are free parameters with ranges constrained by the VLBI analysis (Table 7, note 2); the agreement between the SED theta (about 10.5-11 deg) and the VLBI theta (9.6 +/- 1.6 deg) highlighted in Sections 7 and 8 should therefore be framed as consistency with the VLBI result rather than as an independent confirmation.
  6. [Section 4] The supporting statement that an independent MOJAVE kinematics analysis finds beta > 4 is attributed to a private communication (Kovalev and Homan); since this cannot be verified by readers, please provide a citable public reference or describe the source of this information in a reproducible way.
  7. [Section 7] The reported SED parameters inherit the fixed assumptions theta_open = 5 deg and R_H = 10^18 cm (Eq. 8), the 20% systematic added to the radio, optical, and UV points, and the imposed gamma_cut/gamma_max range; since these choices directly set R and hence the energy densities in Table 8, a brief statement on their influence, or on the lack of a dedicated test of these assumptions, would be useful.
  8. [Section 5.2] Typo: 'milliJanksys' should be 'millijanskys'.
  9. [Equation (2)] In the typeset equation for Delta Amp, the term 'A4mp' appears to be a formatting error for Amp^4; please correct.
  10. [Section 6, Fig. 14] Figure 14 shows optical EVPA values on an axis that reaches only 400 deg, while the text quotes a value of 430 deg; the 360 deg wrap and the axis range should be made consistent for the reader.

Circularity Check

2 steps flagged · score 4.0 of 10

Partial circularity in the SED cross-checks: the SED viewing angle is fitted inside a range set by the VLBI result and then quoted as independent confirmation, and the 'hardening' explanation restates the fitted electron index; the central superluminal-motion measurement is independent.

  1. fitted input called prediction [Section 7, paragraph after Eq. (8), and final SED paragraph; Table 7 note (2)]
    "We also restrict the range of variability of the viewing angle and Lorentz factor of the jet, θ and Γ, to values around those derived from the VLBI analysis. ... These characteristics indicate that this source is indeed a BL Lac object, observed in this case under a rather high viewing angle, as derived from both the VLBI analysis (θ = 9.6±1.6 deg) and the SED models (θ∼ 10.5−11 deg)."

    The SED model's viewing angle is fitted with its allowed range constrained to 'values around those derived from the VLBI analysis' (Table 7 lists θ as free but 'with fit range constrained observationally'). The SED result θ≈10.5–11 deg is therefore not an independent measurement; it is forced to lie near the VLBI value by the fitting prior. Presenting the SED θ as a second derivation that agrees with the VLBI θ is thus a fitted input quoted as confirmation. This does not affect the VLBI measurement itself, but it inflates the evidence for the misaligned-BL-Lac interpretation.

  2. fitted input called prediction [Section 7, paragraph before Table 8; Table 7 (p values)]
    "The variability between the high- and low-emission states can be explained in terms of changes to the distribution of particles —mainly through a hardening of the electron distribution during the high state— as well as a slight increase in the magnetic field B and the bulk Lorentz factor Γ."

    In Table 7, the electron spectral index p is a fully free parameter of each SED fit (p = 1.85 for the high state, p = 2.46 for the low state; note (1): 'Free parameter'). The conclusion that the high state is explained 'mainly through a hardening of the electron distribution' is therefore a restatement of the fitted p values rather than an independent result. Because p was adjusted to reproduce each SED, the inferred spectral hardening is guaranteed by the fit, not tested. This is an interpretive summary of fitted inputs, not a circular step in the VLBI kinematics derivation.

full rationale

The central new result, superluminal motion of VLBI component B4, is derived from independent MOJAVE data: the distance-versus-time fit gives β_app = 5.9 ± 0.8, and the flux-decay fit gives the variability timescale used in the external Jorstad et al. (2005) formulas to obtain δ = 6.0 ± 1.1, Γ = 6.0 ± 1.8, and θ = 9.6 ± 1.6 deg. That chain is not circular: the exponential-decay assumption F = F0 e^{-t/t_var} is adopted from Weaver et al. (2022), an external paper, and the output parameters are not inputs to the fits. The untested exponential functional form is a genuine correctness/systematic-risk concern, but it is not a definitional circularity. The paper also cites an independent MOJAVE-team kinematics check (Kovalev & Homan, private communication) and an independent Doppler estimate by Homan et al. (2021), both external to the fitted SED. The circularity found here is confined to the SED section: the SED viewing angle is fitted within a range set by the VLBI θ and then quoted as corroboration, and the 'hardening' explanation is simply the fitted value of the free parameter p. These steps are ancillary to the VLBI kinematics claim, so the overall circularity score is moderate rather than high. There is no load-bearing self-citation chain.

Assumptions & free parameters 12 free parameters · 8 assumptions · 0 invented entities

The central kinematic claim rests on the VLBI tracking of component B4 and on the assumption that its flux decays exponentially, which is used to estimate the variability timescale that enters the Doppler factor formula. The SED interpretation rests on a one-zone leptonic model with ten or more fitted parameters, many of which are degenerate (Appendix C). The paper is transparent about these dependencies.

free parameters (12)
  • gamma_min = 50.41 (high), 120.10 (low)
    Minimum Lorentz factor of electron distribution, free parameter in JetSeT fit (Table 7).
  • gamma_cut = 5.74e3 (high), 1.30e4 (low)
    Cutoff Lorentz factor, free parameter in SED fit (Table 7).
  • gamma_max = 5.21e5 (high), 4.42e5 (low)
    Maximum Lorentz factor, free parameter constrained by ratio with gamma_cut (Section 7).
  • p = 1.85 (high), 2.46 (low)
    Electron spectral index, free parameter; the conclusion of 'hardening' is based on the difference.
  • N = 0.52e2 (high), 0.51e2 (low)
    Electron normalisation, free parameter in SED fit (Table 7).
  • B = 0.20 G (high), 0.14 G (low)
    Magnetic field, free parameter in SED fit (Table 7).
  • Gamma (bulk Lorentz factor) = 11.47 (high), 8.87 (low)
    Bulk Lorentz factor, free parameter with fit range constrained observationally by VLBI (Table 7).
  • theta (viewing angle) = 10.53 deg (high), 11.09 deg (low)
    Viewing angle, free parameter with fit range constrained observationally by VLBI (Table 7).
  • T_DT = 10^3 K
    Dusty torus temperature, free in low-state fit, fixed for high-state (Table 7).
  • T_disc = 1.16e4 K
    Accretion disc temperature, free in low-state fit, fixed for high-state (Table 7).
  • nu_cut (radio) = 1.15e10 Hz (high), 1.35e10 Hz (low)
    Cutoff frequency of radio power-law component, free parameter (Table 7).
  • nuF_nu,p (radio) = 1.90e-13 erg cm-2 s-1 (high), 2.23e-13 (low)
    Peak flux of radio component, free parameter (Table 7).
assumptions (8)
  • domain assumption The one-zone leptonic (SSC) model with a power-law-plus-exponential-cutoff electron distribution describes the broadband SED of 3C 371 (Section 7).
    This is the theoretical framework used for the SED fitting; if the real emission is hadronic or multi-zone, the derived parameters are not meaningful.
  • domain assumption The flux decay of jet component B4 is exponential, F = F0 e^{-t/t_var} (Section 4).
    This assumption is used to estimate the variability timescale t_var, which is then used to compute the Doppler factor via Jorstad et al. (2005).
  • domain assumption The variability timescale t_var is related to the Doppler factor through the Jorstad et al. (2005) formalism.
    The paper follows Weaver et al. (2022) and Jorstad et al. (2005) to convert the measured decay time into a Doppler factor; the formula is an external calibration.
  • domain assumption The 13 Gyr elliptical galaxy template by Polletta et al. (2007) is appropriate for the host galaxy of 3C 371 (Section 2.3).
    The host galaxy contribution is subtracted using this template, affecting the optical-UV flux densities and colors.
  • domain assumption The accretion disc luminosity is approximated as L_disc = 10 x L_BLR, with L_BLR derived from the H-beta line luminosity (Section 7).
    This scaling (Ghisellini & Tavecchio 2015) is used to set the disc and BLR parameters in the SED model.
  • ad hoc to paper The jet opening angle is fixed to 5 degrees and the distance of the emitting region is fixed to R_H = 10^18 cm (Section 7, Eq. 8).
    These values are assumed to reduce the number of free parameters in the SED fit; different values would change the derived region size R.
  • ad hoc to paper A systematic error of 20% is added to radio, optical, and UV data in the SED fit (Section 7).
    This is a modeling choice to prevent the high-precision photometry from dominating the chi-squared; it affects the best-fit parameters.
  • ad hoc to paper The ratio gamma_cut/gamma_max is restricted to 0.001-0.5 (Section 7).
    This constraint is imposed to reduce degeneracy in the SED fit, but it is not physically required.

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Pith. "Pith review of Multi-wavelength picture of the misaligned BL Lac object 3C 371." pith.science (2026). https://pith.science/paper/UGNVNRBR

@misc{pith2026241204068,
  author       = {Pith},
  title        = {Pith review of: Multi-wavelength picture of the misaligned BL Lac object 3C 371},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/UGNVNRBR}},
  note         = {Machine review of arXiv:2412.04068}
}
abstract

The BL Lac object 3C 371 is one of the targets that are regularly monitored by the Whole Earth Blazar Telescope (WEBT) Collaboration to study blazar variability on both short and long timescales. We aim to evaluate the long-term multiwavelength (MWL) behaviour of 3C 371, comparing it with the results derived for its optical emission in our previous study. For this, we make use of the multi-band campaigns organized by the WEBT Collaboration in optical and radio between January 2018 and December 2020, and of public data from Swift and Fermi satellites and the MOJAVE Very Large Interferometry programme. We evaluate the variability shown by the source in each band with the amplitude variability quantification, as well as possible interband correlation using the z-Discrete Correlation Function. We also present a deep analysis of the optical-UV, X-ray and $\gamma$-ray spectral variability. With the MOJAVE data we perform a kinematics analysis, looking for components propagating along the jet, calculating its kinematics parameters. This set of parameters is later used for the interpretation of the source MWL behaviour, modelling the broadband spectral energy distribution (SED) of the source with theoretical blazar emission scenarios.

Figures

Figures reproduced from arXiv: 2412.04068 by the authors.

Figure 1
Figure 1. Fermi-LAT γ-ray light curve of 3C 371. Top: 15 day binned γ-ray flux light curve between 100 MeV and 300 GeV obtained from the Fermi-LAT data. Middle: γ-ray spectral index as a function of time. Bottom: γ-ray spectral index as a function of γ-ray flux. while they were fixed to the catalogue values for those in the annular region. For this, we used the 4FGL-DR2 catalogue (Ab￾dollahi et al. 2020; Ballet et al. 2020). … view at source ↗
Figure 3
Figure 3. Swift-UVOT optical–UV light curves (observed magni￾tudes) in the period considered in this paper. Red plus symbols correspond to photometry on single exposures; blue dots cor￾respond to the results of co-adding the exposures of the same observations. 2.3. Optical-UV observations: Swift-UVOT The Ultra-Violet and Optical Telescope (UVOT, see Roming et al. 2005) on board the Swift satellite observed 3C 371 during the s… view at source ↗
Figure 4
Figure 4. Radio light curves of 3C 371 compared with the dered [PITH_FULL_IMAGE:figures/full_fig_p004_4.png] view at source ↗
Figures from the paper (9 more)
Figure 5
Figure 5. Figure 5: Amplitude variability for the different bands as a function of frequency. Different markers and colours represent different bands of the spectrum, as indicated in the legend. tion on, for instance, the structure of the jet and the location of the emitting region(s) (se…
Figure 6
Figure 6. Figure 6: ZDCF of the radio, optical, UV, X-ray, and [PITH_FULL_IMAGE:figures/full_fig_p007_6.png]
Figure 7
Figure 7. Figure 7: ZDCF between the 8.5 GHz radio and the γ-ray-band light curves. Different dotted lines denote the contours corre￾sponding to a statistical significance of 1σ, 2σ, and 3σ. evaluated the 8.5 GHz radio and γ-ray correlation in the time pe￾riod considered here, and note th…
Figure 9
Figure 9. Figure 9: Results of the kinematic analysis for component B4. [PITH_FULL_IMAGE:figures/full_fig_p008_9.png]
Figure 10
Figure 10. Figure 10: Comparison of radio flux at 15 GHz and 8.5 GHz. [PITH_FULL_IMAGE:figures/full_fig_p009_10.png]
Figure 11
Figure 11. Figure 11: Dereddened, host-galaxy-corrected colour indices of 3C 371 for the di [PITH_FULL_IMAGE:figures/full_fig_p010_11.png]
Figure 12
Figure 12. Figure 12: Optical SEDs constructed with quasi-simultaneous [PITH_FULL_IMAGE:figures/full_fig_p010_12.png]
Figure 13
Figure 13. Figure 13: Optical R-band flux with respect to the estimated spec￾tral index using a power-law model. The colour bar indicates the MJD of the corresponding SED. 5.4. γ-ray spectral variability We evaluated the γ-ray spectral variability using the 15 day binned Fermi-LAT light cu…
Figure 15
Figure 15. Figure 15: Broadband SED models for the high- (left) and low-brightness states (right) of 3C 371. The top panels contain the broadband SEDs, with the contribution of each component and the best-fit model being represented with different markers, lines, and colours, as indicated …

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Pith tools

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