2015 BL Lac VHE gamma-ray flare

Interestingly, we find that the behaviour in radio, optical, X-rays, and HE {gamma}-rays is very similar to two other observed VHE {gamma}-ray flares. In particular, also during this flare there was an indication of rotation of the optical polarization angle and of activity at the 43GHz core. These repeating patterns indicate a connection between the three events.

We also test modelling of the spectral energy distribution based on constraints from the light curves and VLBA observations, with two different geometrical setups of two-zone inverse Compton models. In addition we model the {gamma}-ray data with the star-jet interaction model. We find that all of the tested emission models are compatible with the fast VHE {gamma}-ray flare, but all have some tension with the multi-wavelength observations.