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Astron. Astrophys. Suppl. Ser. 133, 353-359

The variable sources responsible for the photometric behaviour of OJ 287 in the IR-optical-UV region during 1993-1996

V.A. Hagen-Thorn1 - S.G. Marchenko1 - L.O. Takalo2 - A. Sillanpää2 - T. Pursimo2 - P. Boltwood3 - M. Kidger4 - J.N. Gonzalez-Perez4

1 - Astronomical Institute of St. Petersburg State University, 198904 St. Petersburg, Russia
2 - Tuorla Observatory, Tuorla 21500, Piikkiö, Finland
3 - Boltwood Observatory, 1655 Main St., Stittsville, Ontario, Canada
4 - Instituto de Astrofisica de Canarias, La Laguna, 38200 Tenerife, Spain

Received October 20, 1997; accepted June 22, 1998


An analysis is performed of multicolour observations of OJ 287 carried out during the OJ-94 Project. It is found that in the optical region the variable sources have the same power-law spectrum $(F_\nu\sim\nu^{-1.5})$ irrespective of flux level. In the IR the spectrum flattens during the flare possibly because of synchrotron self-absorption. The comparison of the outburst of 1994 with those of 1971 and 1983 shows that there is a clear correlation between the power of outburst and colour indices of the variable component in each event: the larger is the outburst, the bluer is the variable source, i.e. in more powerful outbursts the energy spectrum of relativistic electrons is flatter.

Key words: BL Lac objects; OJ 287 -- infrared: galaxies

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