Comprehensive Monitoring of Gamma-ray Bright Blazars. I. Statistical Study of Optical, X-ray, and Gamma-ray Spectral Slopes

Abstract

We present $\gamma$-ray, X-ray, ultraviolet, optical, and near-infrared light curves of 33 $\gamma$-ray bright blazars over four years that we have been monitoring since 2008 August with multiple optical, ground-based telescopes and the Swift satellite, and augmented by data from the Fermi Gamma-ray Space Telescope and other publicly available data from Swift. The sample consists of 21 flat-spectrum radio quasars (FSRQs) and 12 BL Lac objects (BL Lacs). We identify quiescent and active states of the sources based on their $\gamma$-ray behavior. We derive $\gamma$-ray, X-ray, and optical spectral indices, ${\alpha }_{\gamma }$, ${\alpha }_X$, and ${\alpha }_o$, respectively ($F_{\nu }\propto {\nu }^{\alpha }$), and construct spectral energy distributions (SEDs) during quiescent and active states. We analyze the relationships between different spectral indices, blazar classes, and activity states. We find (i) significantly steeper $\gamma$-ray spectra of FSRQs than for BL Lacs during quiescent states, but a flattening of the spectra for FSRQs during active states while the BL Lacs show no significant change; (ii) a small difference of ${\alpha }_X$ within each class between states, with BL Lac X-ray spectra significantly steeper than in FSRQs; (iii) a highly peaked distribution of X-ray spectral slopes of FSRQs at $\sim -$0.60, but a very broad distribution of ${\alpha }_X$ of BL Lacs during active states; (iv) flattening of the optical spectra of FSRQs during quiescent states, but no statistically significant change of ${\alpha }_o$ of BL Lacs between states; and (v) a positive correlation between optical and $\gamma$-ray spectral slopes of BL Lacs, with similar values of the slopes. We discuss the findings with respect to the relative prominence of different components of high-energy and optical emission as the flux state changes.

40 pages, 28 figures, 10 Tables. Additional figures at http://www.bu.edu/blazars/VLBAproject.html. Accepted by ApJ

References in corpus (10)

• Probing the Inner Jet of the Quasar PKS 1510-089 with Multi-waveband Monitoring during Strong Gamma-ray Activity
• Bright AGN Source List from the First Three Months of the Fermi Large Area Telescope All-Sky Survey
• Multiwaveband Polarimetric Observations of 15 Active Galactic Nuclei at High Frequencies: Correlated Polarization Behavior
• Host galaxy subtraction of TeV candidate BL Lacertae objects
• Results of WEBT, VLBA and RXTE monitoring of 3C 279 during 2006-2007
• A new activity phase of the blazar 3C 454.3. Multifrequency observations by the WEBT and XMM-Newton in 2007-2008
• Simultaneous multiwavelength observations of the blazar 1ES1959+650 at a low TeV flux
• The Outburst of the Blazar AO 0235+164 in 2006 December: Shock-in-Jet Interpretation
• Multi-wavelength observations of blazar AO 0235+164 in the 2008-2009 flaring state
• Radio-to-UV monitoring of AO 0235+164 by the WEBT and Swift during the 2006--2007 outburst

Cited by in corpus (5)

• Kinematics of Parsec-Scale Jets of Gamma-Ray Blazars at 43~GHz within the VLBA-BU-BLAZAR Program
• Gamma-ray opacity of the anisotropic stratified broad-line regions in blazars
• The connection between the parsec-scale radio jet and gamma-ray flares in the blazar 1156+295
• Flux and polarization variability of OJ 287 during early 2016 outburst
• Fermi Variability Study of the Candidate Pulsar Binary 2FGL~J0523.3-2530