Astronomy and Astrophysics – Astrophysics
Scientific paper
2005-06-08
Astron.J.130:1466-1471,2005
Astronomy and Astrophysics
Astrophysics
to appear on The Astronomical Journal, 17 pages, 7 figures. Fig.2 is given as a separated jpg file
Scientific paper
10.1086/444538
We present the historic light curve of the BL Lac object S5 0716+714, spanning the time interval from 1953 to 2003, built using Asiago archive plates and our recent CCD observations, together with literature data. The source shows an evident long term variability, over which well known short term variations are superposed. In particular, in the period from 1961 to 1983 the mean brightness of S5 0716+714 remained significantly fainter than that observed after 1994. Assuming a constant variation rate of the mean magnitude we can estimate a value of about 0.11 magnitude/year. The simultaneous occurrence of decreasing ejection velocities of superluminal moving components in the jet reported by Bach et al. (2005) suggests that both phenomena are related to the change of the direction of the jet to the line of sight from about 5 to 0.7 degrees for an approximately constant bulk Lorentz factor of about 12. A simple explanation is that of a precessing relativistic jet, which should presently be close to the smallest orientation angle. One can therefore expect in the next ten years a decrease of the mean brightness of about 1 magnitude.
Maesano Maurizio
Massaro Enrico
Montagni Franco
Nesci Roberto
Rossi Claudio
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