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Published January 10, 2012 | Published
Journal Article Open

Contemporaneous VLBA 5 GHz Observations of Large Area Telescope Detected Blazars


The radio properties of blazars detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been observed contemporaneously by the Very Long Baseline Array (VLBA). In total, 232 sources were observed with the VLBA. Ninety sources that were previously observed as part of the VLBA Imaging and Polarimetry Survey (VIPS) have been included in the sample, as well as 142 sources not found in VIPS. This very large, 5 GHz flux-limited sample of active galactic nuclei (AGNs) provides insights into the mechanism that produces strong γ-ray emission. In particular, we see that γ-ray emission is related to strong, uniform magnetic fields in the cores of the host AGN. Included in this sample are non-blazar AGNs such as 3C84, M82, and NGC 6251. For the blazars, the total VLBA radio flux density at 5 GHz correlates strongly with γ-ray flux. The LAT BL Lac objects tend to be similar to the non-LAT BL Lac objects, but the LAT flat-spectrum radio quasars (FSRQs) are significantly different from the non-LAT FSRQs. Strong core polarization is significantly more common among the LAT sources, and core fractional polarization appears to increase during LAT detection.

Additional Information

© 2012 American Astronomical Society. Received 2011 September 19; accepted 2011 November 17; published 2011 December 22. We thank the anonymous referee for helpful comments on the manuscript. We thank Steve Tremblay, Marcello Giroletti and Bob Hastman for their helpful advice and comments. We also thank Steve Myers and Josh Marvil for their help with obtaining EVLA observations of several sources for polarization angle calibration. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This work made use of the Swinburne University of Technology software correlator, developed as part of the Australian Major National Research Facilities Programme and operated under license. The NASA/IPAC Extragalactic Database (NED) is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. We thank NASA for support under FERMI grant GSFC 21078/FERMI08-0051 and the NRAO for support under Student Observing Support Award GSSP10-011.

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Published - Linford2012p16944Astrophys_J.pdf


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