A statistical study of the optical spectral variability in gamma-ray blazars

Abstract

Blazars optical emission is generally dominated by relativistic jets, although the host galaxy, accretion disk and broad line region (BLR) may also contribute significantly. Disentangling their contributions has been challenging for years due to the dominance of the jet. To quantify the contributions to the spectral variability, we use the statistical technique for dimensionality reduction Non-Negative Matrix Factorization on a spectroscopic data set of 26 $\gamma$-ray blazars. This technique allows to model large numbers of spectra in terms of a reduced number of components.We use a priori knowledge to obtain components associated to meaningful physical processes. The sources are classified according to their optical spectrum as host-galaxy dominated BL Lac objects (BL Lacs), BL Lacs, or Flat Spectrum Radio Quasars (FSRQs). Host-galaxy sources show less variability, as expected, and bluer-when-brighter trends, as the other BL Lacs. For FSRQs, more complicated colour-flux behaviours are observed: redder-when-brighter for low states saturating above a certain level and, in some cases, turning to bluer-when-brighter. We are able to reproduce the variability observed during 10 years using only 2 to 4 components, depending on the type. The simplest scenario corresponds to host-galaxy blazars, whose spectra are reconstructed using the stellar population and a power law for the jet. BL Lac spectra are reproduced using from 2 to 4 power laws. Different components can be associated to acceleration/cooling processes taking place in the jet. The reconstruction of FSRQs also incorporates a QSO-like component to account for the BLR, plus a very steep power law, associated to the accretion disk.

arXiv commentAccepted for publication in MNRAS

References in corpus (62)

• Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD
• Unified Schemes for Radio-Loud Active Galactic Nuclei
• Correcting for the Effects of Interstellar Extinction
• Parametric Recovery of Line-of-Sight Velocity Distributions from Absorption-Line Spectra of Galaxies via Penalized Likelihood
• Composite Quasar Spectra From the Sloan Digital Sky Survey
• K-corrections and filter transformations in the ultraviolet, optical, and near infrared
• Improving the full spectrum fitting method: accurate convolution with Gauss-Hermite functions
• On characterising the variability properties of X-ray light curves from active galaxies
• The Spectral Energy Distribution of Fermi bright blazars
• General physical properties of bright Fermi blazars
• Turbulent, Extreme Multi-Zone Model for Simulating Flux and Polarization Variability in Blazars
• The Fourth Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope
• Gamma-ray Light Curves and Variability of Bright Fermi-Detected Blazars
• The 5th edition of the Roma-BZCAT. A short presentation
• The blazar sequence: a new perspective
• SMARTS optical and infrared monitoring of 12 gamma-ray bright blazars
• Multiwavelength Evidence for Quasi-periodic Modulation in the Gamma-ray Blazar PG 1553+113
• A hadronic origin for ultra-high-frequency-peaked BL Lac objects
• Blazar spectral variability as explained by a twisting inhomogeneous jet
• The unprecedented optical outburst of the quasar 3C 454.3. The WEBT campaign of 2004-2005
• Black hole mass estimate for a sample of radio-loud narrow-line Seyfert 1 galaxies
• Quasars and the Big Blue Bump
• Primary black hole spin in OJ287 as determined by the General Relativity centenary flare
• Compton Dominance and the Blazar Sequence
• Machine Learning in Astronomy: a practical overview
• Unprecedented study of the broadband emission of Mrk 421 during flaring activity in March 2010
• Dust and Diffuse Interstellar Bands in the z_a = 0.524 Absorption System toward AO 0235+164
• General Relativistic Magnetohydrodynamic Simulations of the Hard State as a Magnetically-Dominated Accretion Flow
• Systematic search for gamma-ray periodicity in active galactic nuclei detected by the Fermi Large Area Telescope
• Flare-like variability of the Mg IIλ2800Å emission line in the gamma-ray blazar 3C 454.3
• The WEBT Campaign on the Blazar 3C279 in 2006
• Gamma-ray quasi-periodicities of blazars. A cautious approach
• Multifrequency variability of the blazar AO 0235+164. The WEBT campaign in 2004-2005 and long-term SED analysis
• Quasi-periodicities of BL Lac Objects
• The Lack of Torus Emission from BL Lacertae Objects: An Infrared View of Unification with WISE
• A Fast Flare and Direct Redshift Constraint in Far-UV Spectra of the Blazar S50716+714
• Long and short term variability of seven blazars in six near-infrared/optical bands
• Revealing the X-ray Variability of AGN with Principal Component Analysis
• Quasi-periodic behaviour in the optical and γ-ray light curves of blazars 3C 66A and B2 1633+38
• The dual nature of blazar fast variability. Space and ground observations of S5 0716+714
• AGILE detection of a rapid gamma-ray flare from the blazar PKS 1510-089 during the GASP-WEBT monitoring
• Dissecting the long-term emission behaviour of the BL Lac object Mrk 421
• A Consolidated Framework of the Color Variability in Blazars: Long-Term Optical/Near-Infrared Observations of 3C 279
• The complex variability of blazars: Time-scales and periodicity analysis in S4 0954+65
• A unified model for orphan and multi-wavelength blazar flares
• Short Term Flux and Colour Variations in Low-Energy Peaked Blazars
• Infrared properties of blazars: putting the GASP-WEBT sources into context
• Long-term optical-infrared color variability of blazars
• Flare-like Variability of the Mg~II $\lambda$2798 Å Emission Line and UV Fe~II band in the Blazar CTA~102
• Multi-band optical variability of 3C 279 on diverse timescales
• Multi-color optical monitoring of Mrk 501 from 2010 to 2015
• Untangling Optical Emissions of the Jet and Accretion Disk in the Flat-Spectrum Radio Quasar 3C 273 with Reverberation Mapping Data
• Redshift determination of the BL Lac object 3C66A by the detection of its host galaxy cluster at $z=0.340$
• Extreme photo-polarimetric behaviour of the blazar AO 0235+164
• Multi-color optical monitoring of ten blazars from 2005 to 2011
• Long term optical and infrared variability characteristics of Fermi Blazars
• Searching for Quasi-Periodic Modulations in $\gamma$-ray Active Galactic Nuclei
• X-ray spectral variability of blazars using principal component analysis
• Nonnegative Matrix Factorization (NMF) with Heteroscedastic Uncertainties and Missing data
• Learning the Fundamental MIR Spectral Components of Galaxies with Non-Negative Matrix Factorisation
• Optical and Gamma-Ray Variability Behaviors of 3C 454.3 from 2006 to 2011
• The beamed jet and quasar core of the distant blazar 4C 71.07

Cited by in corpus (9)

• Multiwavelength periodicity search in a sample of $\gamma$-ray bright blazars
• Variability and evolution of the optical polarization of a sample of gamma-ray blazars
• The variability of blazars throughout the electromagnetic spectrum
• The optical spectral features of 27 Fermi blazars
• Optical variability of the blazar 3C 371: from minute to year timescales
• Multi-wavelength temporal variability of the blazar PKS 1510-089
• Optical monitoring in southern blazars. Analysis of variability and spectral colour behaviours
• Distinguishing radiation mechanisms and particle populations in blazar jets through long-term multi-band monitoring with RINGO3 and Fermi
• Shortterm optical variability of 4C 29.45