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Astron. Astrophys. 342, L49-L52 (1999)

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Letter to the Editor

The extraordinary optical outburst of ON 231 (W Com) in spring 1998

E. Massaro 1, M. Maesano 1, F. Montagni 1, R. Nesci 1, G. Tosti 2, M. Fiorucci 2, M. Luciani 2, L.O. Takalo 3, A. Sillanpää 3, S. Katajainen 3, P. Keinänen 3, T. Pursimo 3, M. Villata 4, C.M. Raiteri 4, G. De Francesco 4, G. Sobrito 4, Y.S. Efimov 5,6 and N.M. Shakhovskoy 5,6

1 Istituto Astronomico, Unita' GIFCO Roma-1, Universita' "La Sapienza", Via Lancisi 29, I-00161 Roma, Italy
2 Osservatorio Astronomico, Universitá di Perugia, Via A. Pascoli, I-06100 Perugia, Italy
3 Tuorla Observatory, Tuorla, FIN-21500 Piikkio, Finland
4 Osservatorio Astronomico di Torino, Strada Osservatorio 20, I-10025 Pino Torinese, Italy
5 Crimean Astrophysical Observatory, 334413, Nauchny, Crimea, Ukraine
6 Isaac Newton Institute of Chile, Crimean Branch

Received 24 November 1998 / Accepted 13 January 1999


The BL Lac object ON 231 (1219+285, W Com) had an exceptional outburst phase in April-May 1998 and reached the most luminous state, observed at least since the beginning of the century. In this paper our multiband photometric light curves and polarimetric measurements of this event are presented. In the maximum phase the magnitude of ON 231 was R(Cousins)=12.2 and the optical spectral distribution was the flattest ever observed. Our data indicate that the main features of this burst can be explained by the presence of some emission components having different polarisation states and variability time scales ranging from 1 day to several months.

Key words: galaxies: BL Lacertae objects: general – galaxies: BL Lacertae objects: individual: ON 231

Send offprint requests to: E. Massaro (massaro@astro.uniroma1.it)

© European Southern Observatory (ESO) 1999

Online publication: February 23, 1999