Abstract

We report results from our program of monitoring 35 gamma-ray detected blazars (21 quasars, 12 BL Lac objects, and 2 radio galaxies) with the VLBA at 43 GHz (7 mm) from August 2008 to August 2012. We identify superluminal knots in the jets and determine the epochs when the knots pass through the mm-wave core (the ejection time). We construct a gamma-ray light curve for each source using the latest photon and spacecraft data provided by the Fermi LAT and identify sources with gamma-ray flares.

Comparison of ejection times with times of gamma-ray flares reveals different relations between gamma-ray events and disturbances in the parsec-scale jet:

1. the majority of gamma-ray flares (74.6%) and ejections (79.7%) are simultaneous within the uncertainties;
2. the coincidence rate is even higher for events with gamma-ray flux >106 ph/cm2/s, which are more common in quasars (3C454.3, 3C273, 1510-089, 1222+216, 1633+382, 0836+714, and 1730-130);
3. 20% of superluminal ejections in blazars do not trigger gamma-ray activity;
4. 25% of gamma-ray flares, mostly in BL Lacs, are not associated with jet activity seen at 7 mm;
5. 57% of the light curves show simultaneous quiescent states at both gamma-rays and mm-waves.

This result implies that acceleration of electrons to energies exceeding 1 GeV and an intense field of seed photons occurs on parsec scales in the relativistic jets of blazars. This research was supported in part by NASA grants NNX08AV65G, NNX08AV61G, NNX09AT99G, NNX09AU10G, NNX- 10AO59G, and NNX11AQ03G.