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A&A Supplement series, Vol. 129, May I 1998, 577-582

Received June 11; accepted October 31, 1997

Monitoring of AO 0235+164 during a faint stategif

L.O. Takalotex2html_wrap1000 - A. Sillanpäätex2html_wrap1000 - E. Valtaojatex2html_wrap1004 - S. Katajainentex2html_wrap1000 - K. Nilssontex2html_wrap1000 - T. Pursimotex2html_wrap1000 - P. Heinämäkitex2html_wrap1000 - M. Villatatex2html_wrap1014 - C.M. Raiteritex2html_wrap1014 - G. Ghisellinitex2html_wrap1014 - G. De Francescotex2html_wrap1014 - L. Lanteritex2html_wrap1014 - M. Chiabergetex2html_wrap1014 - A. Peilatex2html_wrap1014, P. Boltwoodtex2html_wrap1028 - G. Tostitex2html_wrap1030 - M. Fioruccitex2html_wrap1030 - H. Teräsrantatex2html_wrap1034 - M. Tornikoskitex2html_wrap1034 - P. Teerikorpitex2html_wrap1000

Send offprint request: L.O. Takalo

tex2html_wrap1040  Tuorla Observatory, Tuorla, FIN-21500 Piikkiö, Finland
tex2html_wrap1042  Metsähovi Radio Station, Metsähovi, Kylmälä, Finland
tex2html_wrap1044  Osservatorio Astronomico di Torino, Strada Osservatorio 20, I-10025 Pino Torinese, Italy
tex2html_wrap1046  1655, Main St. Stittsville, Ont, K2S 1N6, Canada
tex2html_wrap1048  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 tex2html_wrap_inline986 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

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