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Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

CIT Disciplines



Astrophysics and Astronomy

Publication Details

Published in the journal Astronomy & Astrophysics in the section Extragalactic Astronomy.

Xilouris, E.M. et al., A&A, 448., 143-153, 2006, reproduced with permission, © ESO

We thank the anonymous referee for useful comments. Skinakas Observatory is a collaborative project of the University of Crete, the Foundation for Research and TechnologyHellas, and the Max-Planck-Institut für extraterrestrische Physik. Part of this work was supported by the European Commission under the TMR program, contract number HPRN-CT-2002-00321.


We have observed S5 2007+777 and 3C 371 in the B and I bands for 13 and 8 nights, respectively, during various observing runs in 2001, 2002 and 2004. The observations resulted in almost evenly sampled light curves, h long. We do not detect any flares within the observed light curves, but we do observe small amplitude, significant variations, in both bands, on time scales of hours and days. The average variability amplitude on time scales of minutes/hours is ~2.5% and ~% in the case of S5 2007+777 and 3C 371, respectively. The average amplitudes increase to % and %, respectively, on time scales of days. We find that the B and I band variations are highly correlated, on both short and long time scales. During the 2004 observations, which resulted in the longest light curves, we observe two well defined flux-decay and rising trends in the light curves of both objects. When the flux decays, we observe significant delays, with the B band flux decaying faster than the flux in the I band. As a result, we also observe significant, flux related spectral variations as well. The flux-spectral relation is rather complicated, with loop-like structures forming during the flux evolution. The presence of spectral variations imply that the observed variability is not caused by geometric effects. On the other hand, our results are fully consistent with the hypothesis that the observed variations are caused by perturbations which affect different regions in the jet of the sources.