A&A Supplement series, Vol. 129, May I 1998, 577-582
Received June 11; accepted October 31, 1997
L.O. Takalo
- A. Sillanpää - E. Valtaoja
- S. Katajainen - K. Nilsson - T. Pursimo
- P. Heinämäki - M. Villata
- C.M. Raiteri - G. Ghisellini - G. De Francesco
- L. Lanteri - M. Chiaberge - A. Peila,
P. Boltwood
- G. Tosti
- M. Fiorucci
- H. Teräsranta
- M. Tornikoski - P. Teerikorpi
Send offprint request: L.O. Takalo
Tuorla Observatory, Tuorla, FIN-21500 Piikkiö, Finland
Metsähovi Radio Station, Metsähovi, Kylmälä, Finland
Osservatorio Astronomico di Torino, Strada Osservatorio 20,
I-10025 Pino Torinese, Italy
1655, Main St. Stittsville, Ont, K2S 1N6, Canada
Cattedra di Astrofisica, Universita di Perugia, Italy
We present the results of the optical and radio monitoring of the BL Lac object
AO 0235+164 during a faint state. In both optical and radio bands the source
has been observed at the faintest ever recorded levels, reaching V=19.80 and
Jy. In the optical bands we still see variability with
amplitudes up to 1.5 magnitudes on timescales from days to weeks. The radio
variability is less dramatic, but in general follows the optical
behaviour. A correlation between general trends in the optical and radio behaviour
of AO 0235+164 may be recognized in the data from
the present monitoring as well as in the historical light curves,
suggesting a "base'' mechanism responsible for the emission at both frequencies.
A good candidate is a synchrotron process in the relativistic jet.
Optical flares with no corresponding radio counterparts have been observed too.
These events may be interpreted in terms of microlensing by a foreground
galaxy.
keywords: Bl lac objects: general; gravitational lensing--AO 0235+164