* Astronomy

Title: S5 1803+78 revisited
Authors: R. Nesci (1), A. Maselli (2), F. Montagni (3) ((1) University La Sapienza, Roma, Italy, (2) INAF-IASF, Palermo, Italy, (3) Greve in Chianti Observatory, Italy)

We report on our optical monitoring of the BL Lac object S5 1803+78 from 1996 to 2011. The source showed no clear periodicity, but a time scale of about 1300 days between major flares is possibly present. No systematic trend of the colour index with flux variations is evident, at variance with other BL Lacs. In one flare, however, the source was bluer in the rising phase and redder in the falling one. Two Gamma-ray flares were detected by Fermi-GST during our monitoring: on the occasion of only one of them we found simultaneous optical brightening. A one-zone Synchrotron Self Compton (SSC) model appears too simple to explain the source behaviour.

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