Correlated variability in the blazar 3C 454.3

Abstract

The blazar 3C 454.3 was revealed by the Fermi Gamma-ray Space Telescope to be in an exceptionally high flux state in 2008 July. Accordingly, we performed a multiwavelength monitoring campaign from 2008 August through December on this blazar using infrared (IR) and optical observations from the Small and Moderate Aperture Research Telescope System telescopes, optical, ultraviolet (UV), and X-ray data from the Swift satellite, and public-release gamma-ray data from Fermi. We find an excellent correlation between the IR, optical, UV, and gamma-ray light curves, with a time lag of less than one day. The amplitude of the IR variability is comparable to that in gamma-rays, and larger than at optical or UV wavelengths. The X-ray flux is not correlated with either the gamma-rays or longer wavelength data. These variability characteristics find a natural explanation in the external Compton model, in which electrons with Lorentz factor γ 103-4 radiate synchrotron emission in the IR-optical and also scatter accretion disk or emission line photons to gamma-ray energies, while much cooler electrons (γ 101-2) produce X-rays by scattering synchrotron or other ambient photons.