Fermi Gamma-ray Space Telescope

Blazar Jets: insights from Radio and Gamma-ray Light Curves

T. J. Pearson
T. Hovatta, W. Max-Moerbeck, A. C. S. Readhead, R. Reeves, J. L. Richards

Abstract:

The Fermi Gamma-Ray Space Telescope provides a unique opportunity for studying nature?s high energy accelerators and the relativistic jets in blazars and microquasars. More than 1500 blazars have have been detected by Fermi, and the gamma-ray flares can often be associated with radio flares. Since 2008, we have been monitoring the flux density of AGN, including most of the northern Fermi blazars, twice weekly at 15 GHz using the Owens Valley Radio Observatory 40m telescope. The program now includes more than 1800 sources, and has recently been augmented with linear polarization measurements. Our monitoring program has sufficient sources, cadence, and sensitivity to enable detailed statistical studies of the variability of different classes of blazars (flat-spectrum radio quasars and BL Lac objects, LSP and HSP blazars). Although the gamma-ray and radio light curves have very different characteristics, cross-correlation using rigorous statistical methods shows significant correlations in some objects. In all such cases the gamma-ray variations precede the radio variations, suggesting that the gamma-ray emission originates upstream of the radio emission. Radio, optical, and gamma-ray light curves, including radio and optical polarization, can now be compared with state-of-the art magnetohydrodynamic simulations to test and refine theoretical models of black holes, accretion disks, and relativistic jets.