A Consolidated Framework of the Color Variability in Blazars: Long-term Optical/Near-infrared Observations of 3C 279

Abstract

We evaluate the optical/near-infrared (OIR) color variability of 3C 279 in both γ-ray flaring and non-flaring states over 7-year timescales using the Small and Medium Aperture Research Telescope System (SMARTS ) in Cerro Tololo, Chile and γ-ray fluxes obtained from the Fermi γ-ray Space Telescope. This observing strategy differs from previous blazar color variability studies in two key ways: 1) the reported color variability is assessed across optical through near-infrared wavelengths, and 2) the color variability is assessed over timescales significantly longer than an individual flare or ground-based observing season. We highlight 3C 279 because of its complex color variability, which is difficult to reconcile with the simple 'redder when brighter' behavior often associated with Flat Spectrum Radio Quasar (FSRQ) color variability. We suggest that the observed OIR color changes depend on a combination of the jet and disk emission. We parametrize this behavior in terms of a single variable, ζ m n , representing a smooth transition from disk-dominated, to a mixed contribution, to a jet-dominated system, which provides an explanation of the long-term OIR color variability in the same blazar over time. This suggests a general scheme that could apply to OIR color variability in other blazars.

Multicolor Optical Monitoring of the Blazar S5 0716+714 from 2017 to 2019

“…For jet dominant emission, the changes of color trends or spectral index trends are likely dominated by the particle acceleration and cooling mechanisms; the BWB trends or FWB trends were thought to be due to electrons being accelerated to preferentially higher energies before radiative cooling, i.e., the spectral evolution of the accelerated electrons to higher intensities and higher spectral frequency; the redder when fainter (RWF) trends or steeper when fainter (SWF) trends occur when the highest-energy electrons suffer a stronger radiative cooling or escape cooling that causes the spectral evolution of the electrons to lower intensities and lower spectral frequency (Isler et al 2017). If the electrons in the emission zone keep the spectral shape unchanged and the source brightens/darkens by changing the number of electrons, then the color trends or spectral index trends keep unchanged when the target source becomes bright or dark, e.g., the acceleration and radiative cooling keep dynamic balance to the electrons.…”

“…The relationships between magnitude and color index could represent a smooth transition from an accretion disk dominant color, to a mixed color from disk and jet, to a jet dominant color (see Fig. 4 from Isler et al 2017). The flux variations of different blazars may correspond to different color behaviours depending on the contributions from jet and accretion disk components.…”

“…The flux variations of different blazars may correspond to different color behaviours depending on the contributions from jet and accretion disk components. Thus, it is possible to take flux variations of different blazars under a consolidated framework of color variations (see Isler et al 2017 for more details).…”

Possible evidence of a supermassive black hole binary with two radio jets in blazar 3C279

“…Very strong variability is observed in all these wavebands on various timescales (hours/days to years). Based on intensive multiwavelength observations and very long baseline interferometry (VLBI) monitorings, studies of the correlation between outbursts at radio, optical/IR, X-ray, and γ-ray wavelengths have provided important information on its variability properties, especially the radiation mechanisms for its X-ray and γ-ray emission and their locations in the jet (e.g., Collmar et al 2010;Chatterjee et al 2012;Agudo et al 2011;Aleksić et al 2014;Cohen et al 2014;Isler et al 2017). Multiwavelength campaigns and studies (e.g., Collmar et al 2010;Rani et al 2017;Hayashida et al 2012Hayashida et al , 2015Kang et al 2015;Larionov et al 2008) have been performed to explore the spectral energy distribution (SED) of its broadband emission.…”

Intra-Night Variability of OJ 287 with Long-Term Multiband Optical Monitoring

“…Ruan et al [45] point out that spectral variability could be the result of hot spots in the accretion disk emission by using a sample of 604 variable quasars. Isler et al [46] suggest colour-magnitude variability should be a continuum rather than a dichotomy. They use empirical data from 3C 279 to explain how blazars can smoothly evolve from a jet-quiescent, disk-dominated colour profile to an actively jet-dominated state and associated colour profile and back to a jet-quiescent state.…”