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Astron. Astrophys. 345, 760-768 (1999)

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OJ 287 and the predicted fade of 1998 *

H. Pietilä 1, L.O. Takalo 1, G. Tosti 2, E. Benítez 3,4, B. Chiattelli 2, R.L.M. Corradi 5, G. Cox 6, J.A. deDiego 3, G. DeFrancesco 9, D. Dultzin-Hacyan 3, P. Heinämäki 1, S. Katajainen 1, P. Keinänen 1, H. Korhonen 7,6, J. Kotilainen 1, M. Lainela 1, J. Licandro 5,8, M. Luciani 2, K. Nilsson 1, T. Pursimo 1, C.M. Raiteri 9, R. Rekola 1, A. Sillanpää 1, G. Sobrito 9, H. Teräsranta 10, M. Villata 9 and A. Zurita 5

1 Tuorla Observatory, University of Turku, FIN-21500 Piikkiö, Finland
2 Cattedra di Astrofisica, Universitá di Perugia, Via A. Pascoli, I-06100 Perugia, Italy
3 Instituto de Astronomía-UNAM, Apdo. 70-264, 04510 México D.F., México
4 Department of Physics, Florida International University, Miami, Fl 33199, USA
5 Instituto de Astrofísica de Canarias, c. Via Lactea S/N, E-38200 La Laguna, Tenerife, Spain
6 Nordic Optical Telescope, Apartado 474, E-38700 S/C de La Palma, Canarias, Spain
7 Division of Astronomy, University of Oulu, P.O. Box 333, FIN-90571 Oulu, Finland
8 Departamento de Astronomía, Facultad de Ciencias, Universidad de la República Oriental del Uruguay,
and Observatorio Astronómico Los Molinos, Tristán Narvaja 1674, 11.200-Montevideo, Uruguay
9 Osservatorio Astronomico di Torino, Strada Osservatorio 20, I-10025 Pino Torinese (TO), Italy
10 Metsähovi Radio Research Station, Metsähovintie 114, FIN-02540 Kylmälä, Finland

Received 3 August 1998 / Accepted 19 February 1999

Abstract

There were predictions that blazar OJ 287 should have faded in late 1997 or early 1998. The observational background for these predictions is the sudden fade of OJ 287 in 1989. Back then, the radio flux decreased steadily for 4-5 months and then the brightness dropped also in the optical region suddenly for 2-3 weeks to all time low values, e.g. V=17.4 mag. The predictions are based on a binary black hole model, where the companion black hole and its accretion disk eclipse the emission areas of the primary black hole. We have made observations of OJ 287 during the time of the predicted fade. The results show that, in the optical, OJ 287 starts to fade almost linearly in December 1997 until mid-February 1998, when it suddenly shows a sharp rise and sharp fade, and starts to get brighter again. The radio observations show no signs of variability, but the radio flux has been very low since the 1995 outburst. We also have earlier observations since Fall 1993 to Spring 1998, which show that the local minimum reached in February 1998 was the lowest since 1995. We have made observations with several telescopes in the optical (UBVRI) and radio (22 and 37 GHz) bands. We discuss the various events in the light curves and their implications on the proposed models, especially the binary black hole model by Lehto & Valtonen (1996), which was used to make the prediction of the time of the fade.

Key words: galaxies: BL Lacertae objects: individual: OJ 287 – galaxies: quasars: general – black hole physics

* Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, observations at the Perugia Observatory, Perugia, Italy, observations at the Observatorio Astronómico Nacional, San Pedro Mártir, Baja California, México, observations at the Torino Observatory, Torino, Italy, observations at the Tuorla Observatory, Piikkiö, Finland, and observations at the Metsähovi Radio Research Station, Metsähovi, Finland.

Send offprint requests to: H. Pietilä (hpietila@astro.utu.fi)

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© European Southern Observatory (ESO) 1999

Online publication: April 28, 1999
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