A Connection Between Shocks in Jets and GeV Gamma-Ray Flares From Blazars

Between 2009.7 and 2012.6 we used the the University of Michigan 26-m telescope to track the centimeter band spectral evolution of the total flux density and of the linear polarization during radio band outbursts temporally associated with gamma ray flares detected by Fermi. Several such events show the expected signature of shocks. These are being modeled using new radiative transfer calculations allowing for propagating shock structures oriented at arbitrary angle to the flow direction. This work identifies shock parameters and flow properties which are similar to those derived in earlier blazar studies and shows that extreme jet conditions are not a requirement for producing the gamma ray flares. We illustrate our procedures, including a new method for separating blended events in the data, using 0420-014 and OJ 287 as examples. This work was supported in part by NASA Fermi GI grants NNX09AU16G, NNX10AP16G, and NNX11AO13G.