The optical spectral features of 27 Fermi blazars

Abstract

A spectral variation accompanied with flux variability is a commonly-observed phenomenon for blazars. In order to further investigate the optical spectral feature of blazars, we have collected the long-term optical V and R band data of 27 blazars (14 BL Lacs and 13 FSRQs), and calculated their optical spectral indices. The results show that the spectral indices vary with respect to the brightness for all of these blazars. In general, the optical spectrum progressively becomes flatter (or steeper), when the brightness increases. However the spectrum changes more and more slowly, until it tends to be stable. In other words, the source becomes bluer (or redder) and then gradually stabilizes when it brightens, which are briefly named the bluer-stable-when-brighter (BSWB) and redder-stable-when-brighter (RSWB) behaviors, respectively. Thirteen of the 14 BL Lacs show the BSWB behavior, with an exception of AO 0235+164. On the contrary, most of FSRQs (10 out of 13) exhibit the RSWB trend. It is confirmed that blazars follow the two universal optical spectral behaviors, namely, BSWB and RSWB. The model of two constant-spectral-index components can well explain the optical spectral features qualitatively and quantitatively. The results illustrate that the optical emission are mainly composed of two stable-color components, i.e., less variable thermal emission and high variable synchrotron radiation. And in most cases, the thermal component of BL Lacs is redder than that of synchrotron radiation, whereas FSRQs are the opposite.

arXiv comment9 pages, 14 figures, accepted by MNRAS

References in corpus (34)

• Leptonic and Hadronic Modeling of Fermi-Detected Blazars
• General physical properties of bright Fermi blazars
• BL Lac Objects in the Synchrotron Proton Blazar Model
• SMARTS optical and infrared monitoring of 12 gamma-ray bright blazars
• Blazars as Ultra-High-Energy Cosmic-Ray Sources: Implications for TeV Gamma-Ray Observations
• 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
• Multi-colour optical monitoring of eight red blazars
• Photopolarimetric Monitoring of Blazars in the Optical and Near-Infrared Bands with the Kanata Telescope. I. Correlations between Flux, Color, and Polarization
• Synchrotron Self-Compton Model for Rapid Nonthermal Flares in Blazars with Frequency-Dependent Time Lags
• An Optical View of BL Lacertae Objects
• The Central Engines of Fermi Blazars
• Spectral Slope Variability of BL Lac Objects in the Optical Band
• Optical Monitoring of BL Lacertae Object S5 0716+714 with a Novel Multi-Peak Interference Filter
• Longterm Optical Monitoring of Bright BL Lacertae Objects with ATOM: Spectral Variability and Multiwavelength Correlations
• Long and short term variability of seven blazars in six near-infrared/optical bands
• The optical variability of flat-spectrum radio quasars in the SDSS stripe 82 region
• The WEBT campaign on the BL Lac object PG 1553+113 in 2013. An analysis of the enigmatic synchrotron emission
• A Consolidated Framework of the Color Variability in Blazars: Long-Term Optical/Near-Infrared Observations of 3C 279
• Characterizing optical variability of OJ 287 in 2016 - 2017
• Long term variability and correlation study of the blazar 3C 454.3 in radio, NIR and optical wavebands
• Short Term Flux and Colour Variations in Low-Energy Peaked Blazars
• Long-term optical-infrared color variability of blazars
• Multicolor Optical Monitoring of the Blazar S5 0716+714 from 2017 to 2019
• Untangling Optical Emissions of the Jet and Accretion Disk in the Flat-Spectrum Radio Quasar 3C 273 with Reverberation Mapping Data
• Multi-color optical monitoring of ten blazars from 2005 to 2011
• Optical Variability of TeV Blazars on long time-scales
• Optical monitoring of BL Lac object S5 0716+714 and FSRQ 3C273 from 2000 to 2014
• Long term optical and infrared variability characteristics of Fermi Blazars
• A statistical study of the optical spectral variability in gamma-ray blazars
• Multiwavelength Analysis of the Variability of the Blazar 3C 273
• A NuSTAR view of powerful gamma-ray loud blazars
• Optical Spectral Variations of a Large Sample of Fermi Blazars
• Optical and Gamma-Ray Variability Behaviors of 3C 454.3 from 2006 to 2011

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