Red quasars are intrinsically X-ray weak with low alpha_OX values, tracing a distinct evolutionary stage of suppressed black hole accretion relative to stellar mass growth.
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M., & Padovani, P
32 Pith papers cite this work, alongside 4,269 external citations. Polarity classification is still indexing.
32
Pith papers citing it
4,269
external citations · Pith
abstract
The appearance of active galactic nuclei (AGN) depends so strongly on orientation that our current classification schemes are dominated by random pointing directions instead of more interesting physical properties. Light from the centers of many AGN is obscured by optically thick circumnuclear matter and in radio-loud AGN, bipolar jets emanating from the nucleus emit light that is relativistically beamed along the jet axes. Understanding the origin and magnitude of radiation anisotropies in AGN allows us to unify different classes of AGN; that is, to identify each single, underlying AGN type that gives rise to different classes through different orientations. This review describes the unification of radio-loud AGN, which include radio galaxies, quasars, and blazars. We describe the classification and properties of AGN and summarize the evidence for anisotropic emission. We outline the two most plausible unified schemes for radio-loud AGN, one linking quasars and luminous radio galaxies and another linking BL~Lac objects and less luminous radio galaxies. Using the formalism appropriate to samples biased by relativistic beaming, we show the population statistics for two schemes are in accordance with available data. We analyze the possible connections between low- and high-luminosity radio-loud AGN. We review potential difficulties with unification and conclude that none currently constitutes a serious problem. We discuss likely complications to unified schemes that are suggested by realistic physical considerations; these will be important to consider when more comprehensive data for larger complete samples become available. We conclude with a list of the ten questions we believe are the most pressing in this field.
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representative citing papers
A causal machine-learning model using variability features from Fermi-LAT light curves predicts blazar flare activity within 90 days with 86% recall on held-out data for one FSRQ.
New publicly available X-ray table models RXToPo and RXagn1 with realistic AGN geometries (torus, polar cone, disk, BLR) generated via RefleX and tested on NGC 424.
SPHEREx data confirm 77 new luminous heavily reddened quasars at 1.5<z<3.9 that are hot-dust poor relative to unobscured quasars, supporting a blow-out feedback phase.
Multimessenger observations and one-zone leptohadronic modeling of PKS 1725+123 during a flare constrain its emission to external Compton gamma-rays, SSC X-rays, and a neutrino rate of about 0.3 events per year peaking at 1 PeV.
J1105+1452 transitioned to a megahertz peaked-spectrum source with a new compact jet of radius ~0.68 pc, apparent velocity ~0.64c, and Doppler factor ~12, while X-ray emission stayed disk-corona dominated.
A changing-look AGN exhibits a rapid accretion-driven spectral transition with broad-line region temperatures of approximately 11,800 K measured via Boltzmann plots and stable black hole mass estimates of 5 times 10 to the 7 solar masses across epochs.
A lens model from Gaia DR3 and HST data combined with a Bayesian test on Chandra observations constrains the X-ray emission origin in lensed quasar J0659 to a 0.020 × 0.010 arcsec ellipse offset 0.014 arcsec from the optical source at 1σ.
Low-luminosity AGN exhibit optical variability structure function slopes that increase with black hole mass from ~0.1 to ~0.3, with amplitude anticorrelated with luminosity, no breaks observed, and variability continuing to rise on 20-year timescales.
Detection of a persistent ~433-day optical QPO in blazar 3C 454.3 at 2.53σ significance using Lomb-Scargle, WWZ, and PDM methods, with a new test for seasonal gaps.
Lya nebulae around unobscured quasars are more extended, asymmetric, and show steeper velocity dispersion declines than those around obscured quasars, supporting an evolutionary AGN model at cosmic noon.
A criterion of |Δg| > 0.4 mag and |Δ(g-r)| > 0.2 mag detects photometric CL-AGN transitions in 9.6% of known hosts with 1.6% false positive rate from simulations.
XRISM observation of 3C 111 finds weak Fe Kβ possibly caused by blueshifted absorption from an ionized wind at 4600 or 17200 km/s, with kinetic power 10^41-10^44 erg/s smaller than the jet power.
VERITAS and multiwavelength observations of the 2017 NGC 1275 gamma-ray flare show harder-when-brighter spectral evolution and support a two-component jet model with 10-degree viewing angle and gamma-ray emission near the C3 radio component.
Changing-look blazars occupy intermediate regions in gamma-ray and X-ray parameter spaces but lie statistically closer to flat-spectrum radio quasars than to BL Lac objects according to centroids, PCA, UMAP, and random-forest classification.
Halo-driven transient rapid growth followed by thermodynamic suppression explains over-massive black holes and Little Red Dots as precursors to standard SMBH-galaxy coevolution.
The January 2010 flare of Mrk421 shows spectral variability consistent with stochastic acceleration, including development of a Maxwellian pile-up component in the particle distribution on three nights.
Five new HI 21-cm absorption detections in LERGs and HERGs at z<0.5 reveal disturbed gas kinematics with velocity offsets over 350 km/s and a 3% detection rate consistent with lower-redshift samples.
Mass-scaled DRW damping timescales in AGNs follow a linear relation with black hole mass (slope 0.35-0.50) for both jetted and non-jetted sources, supporting universal accretion physics.
A census of ~3600 variable compact radio sources at 3 GHz from VLASS epochs 1 and 2, with 5-9% showing >30% flux changes above 20-300 mJy and most consistent with blazars or quasars.
Systematic search of ZTF DR23 data yields catalogs of 28,504 coarse and 1,984 refined AGN flares with public release.
3D RHD simulations of FR0 jets in LEDA 55267 and LEDA 58287 show recollimation shocks driving compactness via turbulence and deceleration, with SED modeling predicting lepto-hadronic emission at TeV energies as a testable forecast.
Reports results from two searches for new radio lenses in existing surveys and discusses the completeness of the population usable for constraining dark matter properties via astrometric perturbations.
Hadronic SED modeling of 103 blazar candidates predicts proton synchrotron peaks in the MeV band for 99 sources and maximum neutrino fluxes detectable by up to 62 sources with next-generation telescopes.
citing papers explorer
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SDSS-V: Revealing a weak accretion state in X-ray selected red quasars
Red quasars are intrinsically X-ray weak with low alpha_OX values, tracing a distinct evolutionary stage of suppressed black hole accretion relative to stellar mass growth.
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Advance warning of $\gamma$-ray blazar flares from \textit{Fermi}-LAT light curves: a strictly causal machine-learning backtest
A causal machine-learning model using variability features from Fermi-LAT light curves predicts blazar flare activity within 90 days with 86% recall on held-out data for one FSRQ.
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The study of the circumnuclear environment of accreting supermassive black holes with realistic X-ray spectral models
New publicly available X-ray table models RXToPo and RXagn1 with realistic AGN geometries (torus, polar cone, disk, BLR) generated via RefleX and tested on NGC 424.
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Hidden Monsters with SPHEREx I: A goldmine for heavily reddened quasars at cosmic noon
SPHEREx data confirm 77 new luminous heavily reddened quasars at 1.5<z<3.9 that are hot-dust poor relative to unobscured quasars, supporting a blow-out feedback phase.
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Zooming in on the GeV $\gamma$-ray flare of the blazar PKS 1725+123 with a multimessenger lens
Multimessenger observations and one-zone leptohadronic modeling of PKS 1725+123 during a flare constrain its emission to external Compton gamma-rays, SSC X-rays, and a neutrino rate of about 0.3 events per year peaking at 1 PeV.
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A Radio Changing-state Jet in the Narrow-line Seyfert 1 Galaxy J1105+1452
J1105+1452 transitioned to a megahertz peaked-spectrum source with a new compact jet of radius ~0.68 pc, apparent velocity ~0.64c, and Doppler factor ~12, while X-ray emission stayed disk-corona dominated.
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Tracing Active Galactic Nuclei Properties Through a Changing-look Event
A changing-look AGN exhibits a rapid accretion-driven spectral transition with broad-line region temperatures of approximately 11,800 K measured via Boltzmann plots and stable black hole mass estimates of 5 times 10 to the 7 solar masses across epochs.
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Determining the spatial origin of X-ray and optical emission in the $z = 3.1$ strongly lensed radio-quiet quasar GraL J065904.1+162909 to hundreds of parsecs
A lens model from Gaia DR3 and HST data combined with a Bayesian test on Chandra observations constrains the X-ray emission origin in lensed quasar J0659 to a 0.020 × 0.010 arcsec ellipse offset 0.014 arcsec from the optical source at 1σ.
-
Optical Variability Structure Function of Low-Luminosity AGN using ATLAS Lightcurves
Low-luminosity AGN exhibit optical variability structure function slopes that increase with black hole mass from ~0.1 to ~0.3, with amplitude anticorrelated with luminosity, no breaks observed, and variability continuing to rise on 20-year timescales.
-
Detection of optical quasi-periodic oscillation in the blazar 3C 454.3
Detection of a persistent ~433-day optical QPO in blazar 3C 454.3 at 2.53σ significance using Lomb-Scargle, WWZ, and PDM methods, with a new test for seasonal gaps.
-
Constraining the nature of active galactic nuclei through circumgalactic Lya emission at z=2-3
Lya nebulae around unobscured quasars are more extended, asymmetric, and show steeper velocity dispersion declines than those around obscured quasars, supporting an evolutionary AGN model at cosmic noon.
-
Identifying Changing-Look AGN Transitions in Light Curve Data with the Zwicky Transient Facility
A criterion of |Δg| > 0.4 mag and |Δ(g-r)| > 0.2 mag detects photometric CL-AGN transitions in 9.6% of known hosts with 1.6% false positive rate from simulations.
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A Weak Fe K$\beta$ Emission Line in the Broad-Line Radio Galaxy 3C 111 Observed with XRISM: An Ionized Wind Absorption Feature?
XRISM observation of 3C 111 finds weak Fe Kβ possibly caused by blueshifted absorption from an ionized wind at 4600 or 17200 km/s, with kinetic power 10^41-10^44 erg/s smaller than the jet power.
-
The exceptional 2017 gamma-ray flare of the radio galaxy NGC 1275: VERITAS and Multiwavelength Observations
VERITAS and multiwavelength observations of the 2017 NGC 1275 gamma-ray flare show harder-when-brighter spectral evolution and support a two-component jet model with 10-degree viewing angle and gamma-ray emission near the C3 radio component.
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Exploring the Transitional Parameter Space of Blazars using Gamma-ray and X-ray Population Diagnostics
Changing-look blazars occupy intermediate regions in gamma-ray and X-ray parameter spaces but lie statistically closer to flat-spectrum radio quasars than to BL Lac objects according to centroids, PCA, UMAP, and random-forest classification.
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Halo-driven Origin and Suppression of Over-massive Black Holes and Little Red Dots
Halo-driven transient rapid growth followed by thermodynamic suppression explains over-massive black holes and Little Red Dots as precursors to standard SMBH-galaxy coevolution.
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The January 2010 flare of Mrk421: Insights from a stochastic acceleration model
The January 2010 flare of Mrk421 shows spectral variability consistent with stochastic acceleration, including development of a Maxwellian pile-up component in the particle distribution on three nights.
-
HI 21-cm absorption in low- and high-excitation radio-loud AGNs at $z<0.5$ from MALS
Five new HI 21-cm absorption detections in LERGs and HERGs at z<0.5 reveal disturbed gas kinematics with velocity offsets over 350 km/s and a 3% detection rate consistent with lower-redshift samples.
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A universal relationship between the variability timescale and black hole mass in black hole jetted and non-jetted accreting systems
Mass-scaled DRW damping timescales in AGNs follow a linear relation with black hole mass (slope 0.35-0.50) for both jetted and non-jetted sources, supporting universal accretion physics.
-
A Census of Variable Radio Sources at $3\,$GHz
A census of ~3600 variable compact radio sources at 3 GHz from VLASS epochs 1 and 2, with 5-9% showing >30% flux changes above 20-300 mJy and most consistent with blazars or quasars.
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A Systematic Search for Active Galactic Nucleus Flares in ZTF Data Release 23
Systematic search of ZTF DR23 data yields catalogs of 28,504 coarse and 1,984 refined AGN flares with public release.
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FR0 radio galaxy jets -- I. linking jet dynamics and high-energy emission in LEDA 55267 and LEDA 58287
3D RHD simulations of FR0 jets in LEDA 55267 and LEDA 58287 show recollimation shocks driving compactness via turbulence and deceleration, with SED modeling predicting lepto-hadronic emission at TeV energies as a testable forecast.
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Taking Inventory of the Most Promising Lensed Radio Sources for Constraining Fundamental Properties of Dark Matter
Reports results from two searches for new radio lenses in existing surveys and discusses the completeness of the population usable for constraining dark matter properties via astrometric perturbations.
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Chasing the neutrino blazar candidates II: SED modeling with hadronic model
Hadronic SED modeling of 103 blazar candidates predicts proton synchrotron peaks in the MeV band for 99 sources and maximum neutrino fluxes detectable by up to 62 sources with next-generation telescopes.
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Spectro-Polarimetric Observations of TeV Sources (SPOTS): First results
First results from the SPOTS campaign reveal low average optical polarization (≲10%) and low magnetic field ordering (F_B ≲0.10) across 14 TeV blazars, with stochastic or rotating polarization angles and wavelength-dependent behavior indicating complex, turbulent jet structures.
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Detectability of Polarized Gamma-ray Emission from Blazar Flares with COSI
Estimates based on 17 years of Fermi LAT data indicate COSI may detect MeV polarization in a small number of blazar flares, with flat-spectrum radio quasars as the top targets.
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Indication of gamma-Ray Quasi-periodicity in GB6 J1037+5711 from Multi-technique Timing Analysis
Multi-technique timing analysis indicates a ~478-day QPO in the gamma-ray emission of BL Lac GB6 J1037+5711.
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Multiphase Gas Structure in the Circumnuclear Region of NGC 5506 Observed with ALMA
New ALMA observations of NGC 5506 show a thick rotating CND where supernova-driven turbulence supplies vertical support and AGN outflow dissociates CO.
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Study of Flat Spectrum Radio Quasars and BL Lacertae Objects as Sources of Diffusive Ultra High-Energy Cosmic Rays
BL Lacs remain consistent with UHECR observations while FSRQs are disfavoured by anisotropy and source density mismatches after propagation modeling.
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X-Ray Spectral Variability of the TeV HBL Blazar PG 1553+113 with XMM-Newton
X-ray spectra of PG 1553+113 over 23 years are best described by log-parabola models in 14 cases and power-laws in 15, with synchrotron peaks indicating variable particle acceleration or cooling in the jet.
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Jet Power Estimates of FSRQs PKS 1441+25 and Ton 599 from Broadband SED Modeling
Jet power estimates for FSRQs PKS 1441+25 and Ton 599 are insensitive to the choice of electron energy distribution model because of lower break energies and external Compton dominance.
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Multi-TeV flaring in nearby High Energy Blazars: A photohadronic scenario
Review applies the photohadronic model with EBL corrections to explain multi-TeV flaring in three nearby blazars.