EDP Sciences Journals List
Advanced Search
Subscriber Authentication Point
Home All issues Volume 448/1 Article
Free access article

Issue A&A
Volume 448, Number 1, March II 2006
Page(s) 143 - 153
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20054054



A&A 448, 143-153 (2006)
DOI: 10.1051/0004-6361:20054054

B and I-band optical micro-variability observations of the BL Lac objects S5 2007+777 and 3C 371

E. M. Xilouris1, I. E. Papadakis2, P. Boumis1, A. Dapergolas1, J. Alikakos1, J. Papamastorakis2, 3, N. Smith4 and C. D. Goudis1, 5

1  Institute of Astronomy & Astrophysics, National Observatory of Athens, I. Metaxa & V. Pavlou, P. Penteli, 15236, Athens, Greece
    e-mail: xilouris@astro.noa.gr
2  Physics Department, University of Crete, PO Box 2208, 71003, Heraklion, Crete, Greece
3  IESL, Foundation for Research and Technology-Hellas, PO Box 1527, 71110, Heraklion, Crete, Greece
4  Department of Applied Physics & Instrumentation, Cork Institute of Technology, Cork, Ireland
5  Department of Physics, University of Patras, 26500, Rio-Patras, Greece

(Received 16 August 2005 / Accepted 30 October 2005 )

Abstract
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, 6-9 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 ~1-1.5% in the case of S5 2007+777 and 3C 371, respectively. The average amplitudes increase to $\sim 5{-}12$% and $\sim 4{-}6$%, 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.


Key words: galaxies: active -- galaxies: BL Lacertae objects: general -- galaxies: BL Lacertae objects: individual: S5 2007+777 -- galaxies: BL Lacertae objects: individual: 3C 371 -- galaxies: jets

SIMBAD Objects



© ESO 2006


What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.