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Published September 11, 2015 | Published + Supplemental Material
Journal Article Open

Locating the γ-ray emission site inFermi/LAT blazars from correlation analysis between 37 GHz radio and γ-ray light curves

Abstract

We address the highly debated issue of constraining the γ-ray emission region in blazars from cross-correlation analysis using discrete correlation function between radio and γ-ray light curves. The significance of the correlations is evaluated using two different approaches: simulating light curves and mixed source correlations. The cross-correlation analysis yielded 26 sources with significant correlations. In most of the sources, the γ-ray peaks lead the radio with time lags in the range +20 and +690 d, whereas in sources 1633+382 and 3C 345 we find the radio emission to lead the γ-rays by −15 and −40 d, respectively. Apart from the individual source study, we stacked the correlations of all sources and also those based on subsamples. The time lag from the stacked correlation is +80 d for the whole sample and the distance travelled by the emission region corresponds to 7 pc. We also compared the start times of activity in radio and γ-rays of the correlated flares using Bayesian block representation. This shows that most of the flares at both wavebands start at almost the same time, implying a co-spatial origin of the activity. The correlated sources show more flares and are brighter in both bands than the uncorrelated ones.

Additional Information

© 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2015 February 11. Received 2015 January 23. In original form 2014 October 3. First published online July 14, 2015. We thank the anonymous referee for providing valuable comments which improved the paper. We are also grateful for the support from the Academy of Finland to our AGN monitoring project (numbers 212656, 210338, 121148 and others). VR acknowledges the support from the Finnish Graduate School in Astronomy and Space Physics. TH was supported by the Academy of Finland project number 267324. We thank Kari Nilsson, Walter Max-Moerbeck, Dmitrios Emmanoulopoulos, Joni Tammi, and Tuomas Savolainen for useful discussions. The VLBA is an instrument of the National Radio Astronomy Observatory, a facility of the NSF, operated under cooperative agreement by Associated Universities, Inc. We also acknowledge the computational resources provided by the Aalto Science-IT project. This research has made use of NASA's Astrophysics Data System.

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Published - MNRAS-2015-Ramakrishnan-1280-94.pdf

Supplemental Material - stv321_figure6_online.pdf

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