A Study of the Long-term Spectral Variations of 3C 66A Observed with the Fermi and Kanata Telescopes

TL;DR

This study analyzes the long-term spectral variations of blazar 3C 66A over two years using Fermi gamma-ray data and optical/infrared observations, revealing different emission behaviors and correlations over time.

Contribution

It provides the first detailed multi-wavelength long-term analysis of 3C 66A, highlighting changes in emission components and external photon energy density.

Findings

Correlation between gamma-ray flux and optical flux in 2008

Weak correlation and increased optical flux in 2009-2010

External seed photon energy density was higher in 2008

Abstract

3C 66A is an intermediate-frequency-peaked BL Lac object detected by the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope. We present a study of the long-term variations of this blazar seen over 2 years at GeV energies with Fermi and in the optical (flux and polarization) and near infrared with the Kanata telescope. In 2008, the first year of the study, we find a correlation between the gamma-ray flux and the measurements taken with the Kanata telescope. This is in contrast to the later measurements performed during 2009--2010 which show only a weak correlation along with a gradual increase of the optical flux. We calculate an external seed photon energy density assuming that the gamma-ray emission is due to external Compton scattering. The energy density of the external photons is found to be higher by a factor of two in 2008 compared to 2009--2010. We conclude that the different behaviors observed between the first year and the later years might be explained by postulating two different emission components.