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Radio and Gamma-ray emission in nearby BL Lacs

Published online by Cambridge University Press:  25 July 2014

G. Giovannini ,
E. Liuzzo ,
B. Boccardi  and
M. Giroletti
G. Giovannini
Affiliation:
Department of Physics and Astronomy, via Ranzani 1, 40123 Bologna, Italy email: ggiovann@ira.inaf.it Radioastronomy Institute/INAF, via Gobetti 101, 40129 Bologna, Italy
E. Liuzzo
Affiliation:
Radioastronomy Institute/INAF, via Gobetti 101, 40129 Bologna, Italy
B. Boccardi
Affiliation:
Max Planck Institute for Radioastronomy, Auf dem Hügel 69 53121 Bonn, Germany.
M. Giroletti
Affiliation:
Radioastronomy Institute/INAF, via Gobetti 101, 40129 Bologna, Italy
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Abstract

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The advent of Fermi is changing our understanding on the radio and γ-ray emission in active galactic nuclei. Unlike pre-Fermi ideas, BL Lac objects are found to be the most abundant emitters in the γ-ray band. However, since they are relatively weak radio sources, most of their parsec-scale structure and their multifrequency properties are poorly understood and/or have not been investigated in a systematic fashion. Here we are analyzing the radio and γ-ray emission properties of a sample of 42 BL Lacs selected with no constraint on their radio and γ-ray emission. Thanks to new Very Long Baseline Array observations at 8 and 15 GHz for the whole sample, we discuss their parsec-scale structure. Parsec-scale radio emission is observed in the majority of the sources at both frequencies. The comparison between our results in radio and gamma-ray bands points out the presence of a large number of faint BL Lacs showing “non-classical” properties such as low source compactness, low core dominance, no gamma-ray emission.

Keywords

BL LacsVLBI
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 9 , Symposium S304: Multiwavelength AGN Surveys and Studies , October 2013 , pp. 200 - 203
Copyright
Copyright © International Astronomical Union 2014 

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