The structure of the October/November 2005 outburst in OJ287 and the precessing binary black hole model

¹ Department of Physics and Tuorla Observatory, University of Turku, Turku, Finland e-mail: mvaltonen2001@yahoo.com
² Department of Physics, The University of The West Indies, St. Augustine, Trinidad and Tobago
³ Herschel Science Centre, European Space Astronomy Centre, Villafranca del Castillo Satellite Tracking Station, Apartado 50727, Madrid, Spain
⁴ INSA
⁵ NORDITA, Blegdamsvej 17, Copenhagen, Denmark
⁶ British Astronomical Association Variable Star Section

Received: 14 September 2006
Accepted: 25 July 2007

Abstract

Aims. The blazar OJ 287 had its biggest optical outburst in over 20 years. It occurred in October/November 2005 and was somewhat expected since similar outbursts had occurred at approximately 12 yr intervals since the early 1900s. However, a strict periodicity would have put the event nearly a year later. Here we ask whether the October/November 2005 outburst was indeed the expected 2006 outburst of OJ287. Did it follow the typical light curve behaviour of such events: a rapid initial rise in just over a week and a slower decay in the following months?

Methods. In this study we use the extensive observations of The British Astronomical Association Variable Star Section, complemented by the data from The American Association of Variable Star Observers. We compare the 2005 outburst with the previous season's first peak of 1983.

Results. We find that the beginning of the 2005 outburst occurred at 2005.76, a few weeks earlier than was reported previously. The timing of the outburst is consistent with the binary black hole model of Lehto and Valtonen. In accordance with this model, we find that the outburst's structural time scale is slower in 2005 than in 1983, while the 2005 outburst was fainter than the 1983 outburst, making the two outbursts about equal in energy. Thus it is quite reasonable to argue that the 2005 outburst was the expected first of the season in the optical light curve of OJ287.