Photopolarimetric monitoring of OJ 287 in 1994–1997

¹ Crimean Astrophysical Observatory and Isaac Newton Institute of Chile, Crimean Branch, Ukraine e-mail: efimov@astro.crao.crimea.ua
² Tuorla Observatory, Tuorla, 21500 Piikkiö, Finland e-mail: takalo@astro.utu.fi

Corresponding author: L. O. Takalo, takalo@astro.utu.fi

Received: 11 December 2000
Accepted: 19 October 2001

Abstract

We present and discuss the UBVRI photopolarimetric data of blazar OJ 287 obtained at the Crimean Astrophysical Observatory from January 1994 until April 1997 as a part of the international OJ-94 campaign. The variations of brightness and linear polarization detected in all used optical bands are similar. No clear correlation was found between the brightness variations and polarization parameters. The most prominent characteristic in the object variability is the apparent continuous rotation of the observed polarization position angle in 1994–1996. The rate of this rotation over two observational seasons in 1994–1995 and 1995–1996 is about 492/day in a clockwise direction. This rate corresponds to the full 360° rotation of the polarization plane in about 73 days. We consider the rotation of the plane of polarization as direct evidence for helical magnetic field structure in the jet of OJ 287.