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Connection between Gamma-Ray Variations and Disturbances in the Jets of Blazars

We perform monthly total and polarized intensity imaging of a sample of $γ$-ray blazars (33 sources) with the Very Long Baseline Array (VLBA) at 43 GHz with the high resolution of 0.1 milliarcseconds. From Summer 2008 to October 2009 several of these blazars triggered Astronomical Telegrams due to a high $γ$-ray state detected by the Fermi Large Area Telescope (LAT): AO 0235+164, 3C 273, 3C 279, PKS 1510-089, and 3C 454.3. We have found that 1) $γ$-ray flares in these blazars occur during an increase of the flux in the 43 GHz VLBI core; 2) strong $γ$-ray activity, consisting of several flares of various amplitudes and durations (weeks to months), is simultaneous with the propagation of a superluminal knot in the inner jet, as found previously for BL Lac (Marscher et al. 2008); 3) coincidence of a superluminal knot with the 43 GHz core precedes the most intense $γ$-ray flare by 36$\pm$24 days. Our results strongly support the idea that the most dramatic $γ$-ray outbursts of blazars originate in the vicinity of the mm-wave core of the relativistic jet. These results are preliminary and should be tested by future monitoring with the VLBA and Fermi.