Abstract:
ABSTRACT
Prompted by a high optical state in 2007 September, the Whole Earth Blazar Telescope consortium organized
an intensive optical, near-IR (JHK) and radio observing campaign on the intermediate BL Lac object 3C 66A
throughout the fall and winter of 2007–2008. In this paper, we present data from 28 observatories in 12 coun-
tries, covering the observing season from late 2007 July through 2008 February. The source remained in a high
optical state throughout the observing period and exhibited several bright flares on timescales of ∼10 days. This
included an exceptional outburst around 2007 September 15–20, reaching a peak brightness at R ∼ 13.4. Our
campaign revealed microvariability with flux changes up to |dR/dt| ∼ 0.02 mag hr−1 . Our observations do not
reveal evidence for systematic spectral variability in the overall high state covered by our campaign, in agree-
ment with previous results. In particular, we do not find evidence for spectral hysteresis in 3C 66A for which
hints were found in an earlier campaign in a somewhat lower flux state. We also did not find any evidencefor spectral lags in the discrete correlation functions between different optical bands.
