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We present a study of the inexplicit connection between radio jet activityand gamma-ray emission of BL Lacertae (BL Lac; 2200+420). We analyze thelong-term millimeter activity of BL Lac via interferometric observations withthe Korean VLBI Network (KVN) obtained at 22, 43, 86, and 129 GHzsimultaneously over three years (from January 2013 to March 2016); during thistime, two gamma-ray outbursts (in November 2013 and March 2015) can be seen ingamma-ray light curves obtained from Fermi observations. The KVN radio core isoptically thick at least up to 86 GHz; there is indication that it might beoptically thin at higher frequencies. To first order, the radio light curvesdecay exponentially over the time span covered by our observations, with decaytimescales of 411+/-85 days, 352+/-79 days, 310+/-57 days, and 283+/-55 days at22, 43, 86, and 129 GHz, respectively. Assuming synchrotron cooling, a coolingtime of around one year is consistent with magnetic field strengths B~2microTand electron Lorentz factors gamma~10,000. Taking into account that our formalmeasurement errors include intrinsic variability and thus over-estimate thestatistical uncertainties, we find that the decay timescale tau scales withfrequency nu like tau~nu^{-0.2}. This relation is much shallower than the oneexpected from opacity effects (core shift), but in agreement with the (sub-)mmradio core being a standing recollimation shock. We do not find convincingradio flux counterparts to the gamma$ray outbursts. The spectral evolution isconsistent with the `generalized shock model' of Valtaoja et al. (1992). Atemporary increase in the core opacity and the emergence of a knot around thetime of the second gamma-ray event indicate that this gamma-ray outburst mightbe an `orphan' flare powered by the `ring of fire' mechanism.

The Millimeter-Radio Emission of BL Lacertae During Two gamma-ray Outbursts