In an effort to locate the sites of emission at different frequencies and physical processes causing variability in blazar jets , we have obtained high time-resolution observations of BL Lacertae over a wide wavelength range : with the Transiting Exoplanet Survey Satellite ( TESS ) at 6,000-10,000 Å with 2-minute cadence ; with the Neil Gehrels Swift satellite at optical , UV , and X-ray bands ; with the Nuclear Spectroscopic Telescope Array at hard X-ray bands ; with the Fermi Large Area Telescope at \gamma -ray energies ; and with the Whole Earth Blazar Telescope for measurement of the optical flux density and polarization .
All light curves are correlated , with similar structure on timescales from hours to days .
The shortest timescale of variability at optical frequencies observed with TESS is \sim 0.5 hr .
The most common timescale is 13 \pm 1 hr , comparable with the minimum timescale of X-ray variability , 14.5 hr .
The multi- \edit 1wavelength variability properties can not be explained by a change solely in the Doppler factor of the emitting plasma .
The polarization behavior implies that there are both ordered and turbulent components to the magnetic field in the jet .
Correlation analysis indicates that the X-ray variations lag behind the \gamma -ray and optical light curves by up to \sim 0.4 days .
The timescales of variability , cross-frequency lags , and polarization properties can be explained by turbulent plasma that is energized by a shock in the jet and subsequently loses energy to synchrotron and inverse Compton radiation in a magnetic field of strength \sim 3 G .